diff --git a/src/app/cmdoptions.cpp b/src/app/cmdoptions.cpp
index 3e23e120b..a0339fbb5 100644
--- a/src/app/cmdoptions.cpp
+++ b/src/app/cmdoptions.cpp
@@ -159,7 +159,7 @@ namespace
                                             .arg(fullParameter()).arg(QLatin1String("<value>")));
         }
 
-        QString value(const QProcessEnvironment &env, const QString &defaultValue = QString()) const
+        QString value(const QProcessEnvironment &env, const QString &defaultValue = {}) const
         {
             QString val = env.value(envVarName());
             return val.isEmpty() ? defaultValue : Utils::String::unquote(val, QLatin1String("'\""));
diff --git a/src/base/bittorrent/magneturi.h b/src/base/bittorrent/magneturi.h
index 07981f85b..d6e8baa8a 100644
--- a/src/base/bittorrent/magneturi.h
+++ b/src/base/bittorrent/magneturi.h
@@ -43,7 +43,7 @@ namespace BitTorrent
     class MagnetUri
     {
     public:
-        explicit MagnetUri(const QString &source = QString());
+        explicit MagnetUri(const QString &source = {});
 
         bool isValid() const;
         InfoHash hash() const;
diff --git a/src/base/bittorrent/session.h b/src/base/bittorrent/session.h
index 7a924a245..45629acd2 100644
--- a/src/base/bittorrent/session.h
+++ b/src/base/bittorrent/session.h
@@ -581,7 +581,7 @@ namespace BitTorrent
 
         bool addTorrent_impl(CreateTorrentParams params, const MagnetUri &magnetUri,
                              TorrentInfo torrentInfo = TorrentInfo(),
-                             const QByteArray &fastresumeData = QByteArray());
+                             const QByteArray &fastresumeData = {});
         bool findIncompleteFiles(TorrentInfo &torrentInfo, QString &savePath) const;
 
         void updateSeedingLimitTimer();
diff --git a/src/base/bittorrent/torrentinfo.h b/src/base/bittorrent/torrentinfo.h
index e10e4e35c..972ff6aab 100644
--- a/src/base/bittorrent/torrentinfo.h
+++ b/src/base/bittorrent/torrentinfo.h
@@ -57,7 +57,7 @@ namespace BitTorrent
         typedef boost::shared_ptr<const libtorrent::torrent_info> NativeConstPtr;
         typedef boost::shared_ptr<libtorrent::torrent_info> NativePtr;
 
-        explicit TorrentInfo(NativeConstPtr nativeInfo = NativeConstPtr());
+        explicit TorrentInfo(NativeConstPtr nativeInfo = {});
         TorrentInfo(const TorrentInfo &other);
 
         static TorrentInfo load(const QByteArray &data, QString *error = nullptr) noexcept;
diff --git a/src/base/http/responsebuilder.cpp b/src/base/http/responsebuilder.cpp
index 916391a4c..13ca09872 100644
--- a/src/base/http/responsebuilder.cpp
+++ b/src/base/http/responsebuilder.cpp
@@ -30,7 +30,7 @@
 
 using namespace Http;
 
-void ResponseBuilder::status(uint code, const QString &text)
+void ResponseBuilder::status(const uint code, const QString &text)
 {
     m_response.status = ResponseStatus(code, text);
 }
diff --git a/src/base/http/server.cpp b/src/base/http/server.cpp
index ce288581f..50a7c1407 100644
--- a/src/base/http/server.cpp
+++ b/src/base/http/server.cpp
@@ -79,7 +79,7 @@ Server::Server(IRequestHandler *requestHandler, QObject *parent)
     dropConnectionTimer->start(CONNECTIONS_SCAN_INTERVAL * 1000);
 }
 
-void Server::incomingConnection(qintptr socketDescriptor)
+void Server::incomingConnection(const qintptr socketDescriptor)
 {
     if (m_connections.size() >= CONNECTIONS_LIMIT) return;
 
@@ -110,7 +110,7 @@ void Server::dropTimedOutConnection()
 {
     QMutableListIterator<Connection *> i(m_connections);
     while (i.hasNext()) {
-        auto connection = i.next();
+        const auto *connection = i.next();
         if (connection->isClosed() || connection->hasExpired(KEEP_ALIVE_DURATION)) {
             delete connection;
             i.remove();
diff --git a/src/base/logger.cpp b/src/base/logger.cpp
index 73dde9a8c..46d980686 100644
--- a/src/base/logger.cpp
+++ b/src/base/logger.cpp
@@ -65,7 +65,7 @@ void Logger::addMessage(const QString &message, const Log::MsgType &type)
 {
     QWriteLocker locker(&m_lock);
 
-    Log::Msg temp = {m_msgCounter++, QDateTime::currentMSecsSinceEpoch(), type, message.toHtmlEscaped()};
+    const Log::Msg temp = {m_msgCounter++, QDateTime::currentMSecsSinceEpoch(), type, message.toHtmlEscaped()};
     m_messages.push_back(temp);
 
     if (m_messages.size() >= MAX_LOG_MESSAGES)
@@ -74,11 +74,11 @@ void Logger::addMessage(const QString &message, const Log::MsgType &type)
     emit newLogMessage(temp);
 }
 
-void Logger::addPeer(const QString &ip, bool blocked, const QString &reason)
+void Logger::addPeer(const QString &ip, const bool blocked, const QString &reason)
 {
     QWriteLocker locker(&m_lock);
 
-    Log::Peer temp = {m_peerCounter++, QDateTime::currentMSecsSinceEpoch(), ip.toHtmlEscaped(), blocked, reason.toHtmlEscaped()};
+    const Log::Peer temp = {m_peerCounter++, QDateTime::currentMSecsSinceEpoch(), ip.toHtmlEscaped(), blocked, reason.toHtmlEscaped()};
     m_peers.push_back(temp);
 
     if (m_peers.size() >= MAX_LOG_MESSAGES)
@@ -87,12 +87,12 @@ void Logger::addPeer(const QString &ip, bool blocked, const QString &reason)
     emit newLogPeer(temp);
 }
 
-QVector<Log::Msg> Logger::getMessages(int lastKnownId) const
+QVector<Log::Msg> Logger::getMessages(const int lastKnownId) const
 {
     QReadLocker locker(&m_lock);
 
-    int diff = m_msgCounter - lastKnownId - 1;
-    int size = m_messages.size();
+    const int diff = m_msgCounter - lastKnownId - 1;
+    const int size = m_messages.size();
 
     if ((lastKnownId == -1) || (diff >= size))
         return m_messages;
@@ -103,12 +103,12 @@ QVector<Log::Msg> Logger::getMessages(int lastKnownId) const
     return m_messages.mid(size - diff);
 }
 
-QVector<Log::Peer> Logger::getPeers(int lastKnownId) const
+QVector<Log::Peer> Logger::getPeers(const int lastKnownId) const
 {
     QReadLocker locker(&m_lock);
 
-    int diff = m_peerCounter - lastKnownId - 1;
-    int size = m_peers.size();
+    const int diff = m_peerCounter - lastKnownId - 1;
+    const int size = m_peers.size();
 
     if ((lastKnownId == -1) || (diff >= size))
         return m_peers;
diff --git a/src/base/logger.h b/src/base/logger.h
index 81ef7e0d1..f6be24b4f 100644
--- a/src/base/logger.h
+++ b/src/base/logger.h
@@ -79,7 +79,7 @@ public:
     static Logger *instance();
 
     void addMessage(const QString &message, const Log::MsgType &type = Log::NORMAL);
-    void addPeer(const QString &ip, bool blocked, const QString &reason = QString());
+    void addPeer(const QString &ip, bool blocked, const QString &reason = {});
     QVector<Log::Msg> getMessages(int lastKnownId = -1) const;
     QVector<Log::Peer> getPeers(int lastKnownId = -1) const;
 
diff --git a/src/base/net/dnsupdater.cpp b/src/base/net/dnsupdater.cpp
index 2660165ee..a262b5c65 100644
--- a/src/base/net/dnsupdater.cpp
+++ b/src/base/net/dnsupdater.cpp
@@ -181,7 +181,7 @@ void DNSUpdater::processIPUpdateReply(const QString &reply)
 {
     Logger *const logger = Logger::instance();
     qDebug() << Q_FUNC_INFO << reply;
-    QString code = reply.split(' ').first();
+    const QString code = reply.split(' ').first();
     qDebug() << Q_FUNC_INFO << "Code:" << code;
 
     if ((code == "good") || (code == "nochg")) {
@@ -284,7 +284,7 @@ void DNSUpdater::updateCredentials()
     }
 }
 
-QUrl DNSUpdater::getRegistrationUrl(int service)
+QUrl DNSUpdater::getRegistrationUrl(const int service)
 {
     switch (service) {
     case DNS::DYNDNS:
diff --git a/src/base/net/downloadhandler.cpp b/src/base/net/downloadhandler.cpp
index 1515eb83c..d94efe22c 100644
--- a/src/base/net/downloadhandler.cpp
+++ b/src/base/net/downloadhandler.cpp
@@ -135,7 +135,7 @@ void Net::DownloadHandler::processFinishedDownload()
     this->deleteLater();
 }
 
-void Net::DownloadHandler::checkDownloadSize(qint64 bytesReceived, qint64 bytesTotal)
+void Net::DownloadHandler::checkDownloadSize(const qint64 bytesReceived, const qint64 bytesTotal)
 {
     QString msg = tr("The file size is %1. It exceeds the download limit of %2.");
 
diff --git a/src/base/net/downloadmanager.cpp b/src/base/net/downloadmanager.cpp
index da29e4c2f..680d2e233 100644
--- a/src/base/net/downloadmanager.cpp
+++ b/src/base/net/downloadmanager.cpp
@@ -58,7 +58,7 @@ namespace
         explicit NetworkCookieJar(QObject *parent = nullptr)
             : QNetworkCookieJar(parent)
         {
-            QDateTime now = QDateTime::currentDateTime();
+            const QDateTime now = QDateTime::currentDateTime();
             QList<QNetworkCookie> cookies = Preferences::instance()->getNetworkCookies();
             for (const QNetworkCookie &cookie : asConst(Preferences::instance()->getNetworkCookies())) {
                 if (cookie.isSessionCookie() || (cookie.expirationDate() <= now))
@@ -70,7 +70,7 @@ namespace
 
         ~NetworkCookieJar() override
         {
-            QDateTime now = QDateTime::currentDateTime();
+            const QDateTime now = QDateTime::currentDateTime();
             QList<QNetworkCookie> cookies = allCookies();
             for (const QNetworkCookie &cookie : asConst(allCookies())) {
                 if (cookie.isSessionCookie() || (cookie.expirationDate() <= now))
@@ -85,7 +85,7 @@ namespace
 
         QList<QNetworkCookie> cookiesForUrl(const QUrl &url) const override
         {
-            QDateTime now = QDateTime::currentDateTime();
+            const QDateTime now = QDateTime::currentDateTime();
             QList<QNetworkCookie> cookies = QNetworkCookieJar::cookiesForUrl(url);
             for (const QNetworkCookie &cookie : asConst(QNetworkCookieJar::cookiesForUrl(url))) {
                 if (!cookie.isSessionCookie() && (cookie.expirationDate() <= now))
@@ -97,7 +97,7 @@ namespace
 
         bool setCookiesFromUrl(const QList<QNetworkCookie> &cookieList, const QUrl &url) override
         {
-            QDateTime now = QDateTime::currentDateTime();
+            const QDateTime now = QDateTime::currentDateTime();
             QList<QNetworkCookie> cookies = cookieList;
             for (const QNetworkCookie &cookie : cookieList) {
                 if (!cookie.isSessionCookie() && (cookie.expirationDate() <= now))
@@ -222,8 +222,8 @@ bool Net::DownloadManager::hasSupportedScheme(const QString &url)
 
 void Net::DownloadManager::applyProxySettings()
 {
-    auto proxyManager = ProxyConfigurationManager::instance();
-    ProxyConfiguration proxyConfig = proxyManager->proxyConfiguration();
+    const auto *proxyManager = ProxyConfigurationManager::instance();
+    const ProxyConfiguration proxyConfig = proxyManager->proxyConfiguration();
     QNetworkProxy proxy;
 
     if (!proxyManager->isProxyOnlyForTorrents() && (proxyConfig.type != ProxyType::None)) {
@@ -253,10 +253,10 @@ void Net::DownloadManager::applyProxySettings()
     m_networkManager.setProxy(proxy);
 }
 
-void Net::DownloadManager::handleReplyFinished(QNetworkReply *reply)
+void Net::DownloadManager::handleReplyFinished(const QNetworkReply *reply)
 {
     const ServiceID id = ServiceID::fromURL(reply->url());
-    auto waitingJobsIter = m_waitingJobs.find(id);
+    const auto waitingJobsIter = m_waitingJobs.find(id);
     if ((waitingJobsIter == m_waitingJobs.end()) || waitingJobsIter.value().isEmpty()) {
         m_busyServices.remove(id);
         return;
@@ -311,7 +311,7 @@ qint64 Net::DownloadRequest::limit() const
     return m_limit;
 }
 
-Net::DownloadRequest &Net::DownloadRequest::limit(qint64 value)
+Net::DownloadRequest &Net::DownloadRequest::limit(const qint64 value)
 {
     m_limit = value;
     return *this;
@@ -322,7 +322,7 @@ bool Net::DownloadRequest::saveToFile() const
     return m_saveToFile;
 }
 
-Net::DownloadRequest &Net::DownloadRequest::saveToFile(bool value)
+Net::DownloadRequest &Net::DownloadRequest::saveToFile(const bool value)
 {
     m_saveToFile = value;
     return *this;
@@ -333,7 +333,7 @@ bool Net::DownloadRequest::handleRedirectToMagnet() const
     return m_handleRedirectToMagnet;
 }
 
-Net::DownloadRequest &Net::DownloadRequest::handleRedirectToMagnet(bool value)
+Net::DownloadRequest &Net::DownloadRequest::handleRedirectToMagnet(const bool value)
 {
     m_handleRedirectToMagnet = value;
     return *this;
diff --git a/src/base/net/downloadmanager.h b/src/base/net/downloadmanager.h
index a04701c89..3e83dbc3f 100644
--- a/src/base/net/downloadmanager.h
+++ b/src/base/net/downloadmanager.h
@@ -115,7 +115,7 @@ namespace Net
         explicit DownloadManager(QObject *parent = nullptr);
 
         void applyProxySettings();
-        void handleReplyFinished(QNetworkReply *reply);
+        void handleReplyFinished(const QNetworkReply *reply);
 
         static DownloadManager *m_instance;
         QNetworkAccessManager m_networkManager;
diff --git a/src/base/net/geoipmanager.cpp b/src/base/net/geoipmanager.cpp
index a659a4271..541ebad0d 100644
--- a/src/base/net/geoipmanager.cpp
+++ b/src/base/net/geoipmanager.cpp
@@ -95,7 +95,7 @@ void GeoIPManager::loadDatabase()
         m_geoIPDatabase = nullptr;
     }
 
-    QString filepath = Utils::Fs::expandPathAbs(
+    const QString filepath = Utils::Fs::expandPathAbs(
         QString("%1%2/%3").arg(specialFolderLocation(SpecialFolder::Data), GEOIP_FOLDER, GEOIP_FILENAME));
 
     QString error;
@@ -118,7 +118,7 @@ void GeoIPManager::manageDatabaseUpdate()
 
 void GeoIPManager::downloadDatabaseFile()
 {
-    DownloadHandler *handler = DownloadManager::instance()->download({DATABASE_URL});
+    const DownloadHandler *handler = DownloadManager::instance()->download({DATABASE_URL});
     connect(handler, static_cast<void (Net::DownloadHandler::*)(const QString &, const QByteArray &)>(&Net::DownloadHandler::downloadFinished)
             , this, &GeoIPManager::downloadFinished);
     connect(handler, &Net::DownloadHandler::downloadFailed, this, &GeoIPManager::downloadFailed);
@@ -434,7 +434,7 @@ void GeoIPManager::downloadFinished(const QString &url, QByteArray data)
             Logger::instance()->addMessage(tr("GeoIP database loaded. Type: %1. Build time: %2.")
                 .arg(m_geoIPDatabase->type(), m_geoIPDatabase->buildEpoch().toString()),
                 Log::INFO);
-            QString targetPath = Utils::Fs::expandPathAbs(
+            const QString targetPath = Utils::Fs::expandPathAbs(
                         specialFolderLocation(SpecialFolder::Data) + GEOIP_FOLDER);
             if (!QDir(targetPath).exists())
                 QDir().mkpath(targetPath);
diff --git a/src/base/net/portforwarder.cpp b/src/base/net/portforwarder.cpp
index f5d6edb8e..15314081e 100644
--- a/src/base/net/portforwarder.cpp
+++ b/src/base/net/portforwarder.cpp
@@ -78,7 +78,7 @@ bool PortForwarder::isEnabled() const
     return m_active;
 }
 
-void PortForwarder::setEnabled(bool enabled)
+void PortForwarder::setEnabled(const bool enabled)
 {
     if (m_active != enabled) {
         if (enabled)
@@ -90,7 +90,7 @@ void PortForwarder::setEnabled(bool enabled)
     }
 }
 
-void PortForwarder::addPort(quint16 port)
+void PortForwarder::addPort(const quint16 port)
 {
     if (!m_mappedPorts.contains(port)) {
         m_mappedPorts.insert(port, 0);
@@ -99,7 +99,7 @@ void PortForwarder::addPort(quint16 port)
     }
 }
 
-void PortForwarder::deletePort(quint16 port)
+void PortForwarder::deletePort(const quint16 port)
 {
     if (m_mappedPorts.contains(port)) {
         if (m_active)
diff --git a/src/base/net/private/geoipdatabase.cpp b/src/base/net/private/geoipdatabase.cpp
index 014ef40f4..28dbe9f49 100644
--- a/src/base/net/private/geoipdatabase.cpp
+++ b/src/base/net/private/geoipdatabase.cpp
@@ -74,7 +74,7 @@ struct DataFieldDescriptor
     };
 };
 
-GeoIPDatabase::GeoIPDatabase(quint32 size)
+GeoIPDatabase::GeoIPDatabase(const quint32 size)
     : m_ipVersion(0)
     , m_recordSize(0)
     , m_nodeCount(0)
@@ -165,7 +165,7 @@ QString GeoIPDatabase::lookup(const QHostAddress &hostAddr) const
 
     for (int i = 0; i < 16; ++i) {
         for (int j = 0; j < 8; ++j) {
-            bool right = static_cast<bool>((addr[i] >> (7 - j)) & 1);
+            const bool right = static_cast<bool>((addr[i] >> (7 - j)) & 1);
             // Interpret the left/right record as number
             if (right)
                 ptr += m_recordBytes;
@@ -183,7 +183,7 @@ QString GeoIPDatabase::lookup(const QHostAddress &hostAddr) const
                 if (country.isEmpty()) {
                     const quint32 offset = id - m_nodeCount - sizeof(DATA_SECTION_SEPARATOR);
                     quint32 tmp = offset + m_indexSize + sizeof(DATA_SECTION_SEPARATOR);
-                    QVariant val = readDataField(tmp);
+                    const QVariant val = readDataField(tmp);
                     if (val.userType() == QMetaType::QVariantHash) {
                         country = val.toHash()["country"].toHash()["iso_code"].toString();
                         m_countries[id] = country;
@@ -226,8 +226,8 @@ bool GeoIPDatabase::parseMetadata(const QVariantHash &metadata, QString &error)
 
     CHECK_METADATA_REQ(binary_format_major_version, UShort);
     CHECK_METADATA_REQ(binary_format_minor_version, UShort);
-    uint versionMajor = metadata.value("binary_format_major_version").toUInt();
-    uint versionMinor = metadata.value("binary_format_minor_version").toUInt();
+    const uint versionMajor = metadata.value("binary_format_major_version").toUInt();
+    const uint versionMinor = metadata.value("binary_format_minor_version").toUInt();
     if (versionMajor != 2) {
         error = tr("Unsupported database version: %1.%2").arg(versionMajor).arg(versionMinor);
         return false;
@@ -254,7 +254,7 @@ bool GeoIPDatabase::parseMetadata(const QVariantHash &metadata, QString &error)
     m_indexSize = m_nodeCount * m_nodeSize;
 
     CHECK_METADATA_REQ(database_type, QString);
-    QString dbType = metadata.value("database_type").toString();
+    const QString dbType = metadata.value("database_type").toString();
     if (dbType != DB_TYPE) {
         error = tr("Invalid database type: %1").arg(dbType);
         return false;
@@ -299,7 +299,7 @@ QVariantHash GeoIPDatabase::readMetadata() const
         if (m_size > MAX_METADATA_SIZE)
             index += (m_size - MAX_METADATA_SIZE); // from begin of all data
         auto offset = static_cast<quint32>(index + strlen(METADATA_BEGIN_MARK));
-        QVariant metadata = readDataField(offset);
+        const QVariant metadata = readDataField(offset);
         if (metadata.userType() == QMetaType::QVariantHash)
             return metadata.toHash();
     }
@@ -390,12 +390,12 @@ QVariant GeoIPDatabase::readDataField(quint32 &offset) const
 bool GeoIPDatabase::readDataFieldDescriptor(quint32 &offset, DataFieldDescriptor &out) const
 {
     const uchar *dataPtr = m_data + offset;
-    int availSize = m_size - offset;
+    const int availSize = m_size - offset;
     if (availSize < 1) return false;
 
     out.fieldType = static_cast<DataType>((dataPtr[0] & 0xE0) >> 5);
     if (out.fieldType == DataType::Pointer) {
-        int size = ((dataPtr[0] & 0x18) >> 3);
+        const int size = ((dataPtr[0] & 0x18) >> 3);
         if (availSize < (size + 2)) return false;
 
         if (size == 0)
@@ -442,7 +442,7 @@ bool GeoIPDatabase::readDataFieldDescriptor(quint32 &offset, DataFieldDescriptor
     return true;
 }
 
-void GeoIPDatabase::fromBigEndian(uchar *buf, quint32 len) const
+void GeoIPDatabase::fromBigEndian(uchar *buf, const quint32 len) const
 {
 #if (Q_BYTE_ORDER == Q_LITTLE_ENDIAN)
     std::reverse(buf, buf + len);
@@ -452,7 +452,7 @@ void GeoIPDatabase::fromBigEndian(uchar *buf, quint32 len) const
 #endif
 }
 
-QVariant GeoIPDatabase::readMapValue(quint32 &offset, quint32 count) const
+QVariant GeoIPDatabase::readMapValue(quint32 &offset, const quint32 count) const
 {
     QVariantHash map;
 
@@ -461,7 +461,7 @@ QVariant GeoIPDatabase::readMapValue(quint32 &offset, quint32 count) const
         if (field.userType() != QMetaType::QString)
             return {};
 
-        QString key = field.toString();
+        const QString key = field.toString();
         field = readDataField(offset);
         if (field.userType() == QVariant::Invalid)
             return {};
@@ -472,12 +472,12 @@ QVariant GeoIPDatabase::readMapValue(quint32 &offset, quint32 count) const
     return map;
 }
 
-QVariant GeoIPDatabase::readArrayValue(quint32 &offset, quint32 count) const
+QVariant GeoIPDatabase::readArrayValue(quint32 &offset, const quint32 count) const
 {
     QVariantList array;
 
     for (quint32 i = 0; i < count; ++i) {
-        QVariant field = readDataField(offset);
+        const QVariant field = readDataField(offset);
         if (field.userType() == QVariant::Invalid)
             return {};
 
diff --git a/src/base/net/smtp.cpp b/src/base/net/smtp.cpp
index 452a3a6d0..4cffa215c 100644
--- a/src/base/net/smtp.cpp
+++ b/src/base/net/smtp.cpp
@@ -140,8 +140,8 @@ void Smtp::sendMail(const QString &from, const QString &to, const QString &subje
                 + "\r\n";
     // Encode the body in base64
     QString crlfBody = body;
-    QByteArray b = crlfBody.replace("\n", "\r\n").toUtf8().toBase64();
-    int ct = b.length();
+    const QByteArray b = crlfBody.replace("\n", "\r\n").toUtf8().toBase64();
+    const int ct = b.length();
     for (int i = 0; i < ct; i += 78)
         m_message += b.mid(i, 78);
     m_from = from;
@@ -173,13 +173,13 @@ void Smtp::readyRead()
     // SMTP is line-oriented
     m_buffer += m_socket->readAll();
     while (true) {
-        int pos = m_buffer.indexOf("\r\n");
+        const int pos = m_buffer.indexOf("\r\n");
         if (pos < 0) return; // Loop exit condition
-        QByteArray line = m_buffer.left(pos);
+        const QByteArray line = m_buffer.left(pos);
         m_buffer = m_buffer.mid(pos + 2);
         qDebug() << "Response line:" << line;
         // Extract response code
-        QByteArray code = line.left(3);
+        const QByteArray code = line.left(3);
 
         switch (m_state) {
         case Init:
@@ -285,7 +285,7 @@ void Smtp::readyRead()
     }
 }
 
-QByteArray Smtp::encodeMimeHeader(const QString &key, const QString &value, QTextCodec *latin1, const QByteArray &prefix)
+QByteArray Smtp::encodeMimeHeader(const QString &key, const QString &value, const QTextCodec *latin1, const QByteArray &prefix)
 {
     QByteArray rv = "";
     QByteArray line = key.toLatin1() + ": ";
@@ -307,10 +307,10 @@ QByteArray Smtp::encodeMimeHeader(const QString &key, const QString &value, QTex
     else {
         // The text cannot be losslessly encoded as Latin-1. Therefore, we
         // must use base64 encoding.
-        QByteArray utf8 = value.toUtf8();
+        const QByteArray utf8 = value.toUtf8();
         // Use base64 encoding
-        QByteArray base64 = utf8.toBase64();
-        int ct = base64.length();
+        const QByteArray base64 = utf8.toBase64();
+        const int ct = base64.length();
         line += "=?utf-8?b?";
         for (int i = 0; i < ct; i += 4) {
             /*if (line.length() > 72) {
@@ -326,7 +326,7 @@ QByteArray Smtp::encodeMimeHeader(const QString &key, const QString &value, QTex
 
 void Smtp::ehlo()
 {
-    QByteArray address = determineFQDN();
+    const QByteArray address = determineFQDN();
     m_socket->write("ehlo " + address + "\r\n");
     m_socket->flush();
     m_state = EhloSent;
@@ -334,13 +334,13 @@ void Smtp::ehlo()
 
 void Smtp::helo()
 {
-    QByteArray address = determineFQDN();
+    const QByteArray address = determineFQDN();
     m_socket->write("helo " + address + "\r\n");
     m_socket->flush();
     m_state = HeloSent;
 }
 
-void Smtp::parseEhloResponse(const QByteArray &code, bool continued, const QString &line)
+void Smtp::parseEhloResponse(const QByteArray &code, const bool continued, const QString &line)
 {
     if (code != "250") {
         // Error
@@ -407,7 +407,7 @@ void Smtp::authenticate()
     // AUTH extension is supported, check which
     // authentication modes are supported by
     // the server
-    QStringList auth = m_extensions["AUTH"].toUpper().split(' ', QString::SkipEmptyParts);
+    const QStringList auth = m_extensions["AUTH"].toUpper().split(' ', QString::SkipEmptyParts);
     if (auth.contains("CRAM-MD5")) {
         qDebug() << "Using CRAM-MD5 authentication...";
         authCramMD5();
@@ -454,7 +454,7 @@ void Smtp::authCramMD5(const QByteArray &challenge)
         m_state = AuthRequestSent;
     }
     else {
-        QByteArray response = m_username.toLatin1() + ' '
+        const QByteArray response = m_username.toLatin1() + ' '
                               + hmacMD5(m_password.toLatin1(), QByteArray::fromBase64(challenge)).toHex();
         m_socket->write(response.toBase64() + "\r\n");
         m_socket->flush();
@@ -514,23 +514,23 @@ QString Smtp::getCurrentDateTime() const
     const QDate nowDate = nowDateTime.date();
     const QLocale eng(QLocale::English);
 
-    QString timeStr = nowDateTime.time().toString("HH:mm:ss");
-    QString weekDayStr = eng.dayName(nowDate.dayOfWeek(), QLocale::ShortFormat);
-    QString dayStr = QString::number(nowDate.day());
-    QString monthStr = eng.monthName(nowDate.month(), QLocale::ShortFormat);
-    QString yearStr = QString::number(nowDate.year());
+    const QString timeStr = nowDateTime.time().toString("HH:mm:ss");
+    const QString weekDayStr = eng.dayName(nowDate.dayOfWeek(), QLocale::ShortFormat);
+    const QString dayStr = QString::number(nowDate.day());
+    const QString monthStr = eng.monthName(nowDate.month(), QLocale::ShortFormat);
+    const QString yearStr = QString::number(nowDate.year());
 
     QDateTime tmp = nowDateTime;
     tmp.setTimeSpec(Qt::UTC);
-    int timeOffsetHour = nowDateTime.secsTo(tmp) / 3600;
-    int timeOffsetMin = nowDateTime.secsTo(tmp) / 60 - (60 * timeOffsetHour);
-    int timeOffset = timeOffsetHour * 100 + timeOffsetMin;
+    const int timeOffsetHour = nowDateTime.secsTo(tmp) / 3600;
+    const int timeOffsetMin = nowDateTime.secsTo(tmp) / 60 - (60 * timeOffsetHour);
+    const int timeOffset = timeOffsetHour * 100 + timeOffsetMin;
     // buf size = 11 to avoid format truncation warnings from snprintf
     char buf[11] = {0};
     std::snprintf(buf, sizeof(buf), "%+05d", timeOffset);
-    QString timeOffsetStr = buf;
+    const QString timeOffsetStr = buf;
 
-    QString ret = weekDayStr + ", " + dayStr + ' ' + monthStr + ' ' + yearStr + ' ' + timeStr + ' ' + timeOffsetStr;
+    const QString ret = weekDayStr + ", " + dayStr + ' ' + monthStr + ' ' + yearStr + ' ' + timeStr + ' ' + timeOffsetStr;
     return ret;
 }
 
diff --git a/src/base/net/smtp.h b/src/base/net/smtp.h
index d1944bd49..b8775f895 100644
--- a/src/base/net/smtp.h
+++ b/src/base/net/smtp.h
@@ -90,13 +90,13 @@ namespace Net
             AuthCramMD5
         };
 
-        QByteArray encodeMimeHeader(const QString &key, const QString &value, QTextCodec *latin1, const QByteArray &prefix = QByteArray());
+        QByteArray encodeMimeHeader(const QString &key, const QString &value, const QTextCodec *latin1, const QByteArray &prefix = {});
         void ehlo();
         void helo();
         void parseEhloResponse(const QByteArray &code, bool continued, const QString &line);
         void authenticate();
         void startTLS();
-        void authCramMD5(const QByteArray &challenge = QByteArray());
+        void authCramMD5(const QByteArray &challenge = {});
         void authPlain();
         void authLogin();
         void logError(const QString &msg);
diff --git a/src/base/preferences.cpp b/src/base/preferences.cpp
index b07aad832..69475fad5 100644
--- a/src/base/preferences.cpp
+++ b/src/base/preferences.cpp
@@ -104,7 +104,7 @@ bool Preferences::deleteTorrentFilesAsDefault() const
     return value("Preferences/General/DeleteTorrentsFilesAsDefault", false).toBool();
 }
 
-void Preferences::setDeleteTorrentFilesAsDefault(bool del)
+void Preferences::setDeleteTorrentFilesAsDefault(const bool del)
 {
     setValue("Preferences/General/DeleteTorrentsFilesAsDefault", del);
 }
@@ -114,7 +114,7 @@ bool Preferences::confirmOnExit() const
     return value("Preferences/General/ExitConfirm", true).toBool();
 }
 
-void Preferences::setConfirmOnExit(bool confirm)
+void Preferences::setConfirmOnExit(const bool confirm)
 {
     setValue("Preferences/General/ExitConfirm", confirm);
 }
@@ -124,7 +124,7 @@ bool Preferences::speedInTitleBar() const
     return value("Preferences/General/SpeedInTitleBar", false).toBool();
 }
 
-void Preferences::showSpeedInTitleBar(bool show)
+void Preferences::showSpeedInTitleBar(const bool show)
 {
     setValue("Preferences/General/SpeedInTitleBar", show);
 }
@@ -134,7 +134,7 @@ bool Preferences::useAlternatingRowColors() const
     return value("Preferences/General/AlternatingRowColors", true).toBool();
 }
 
-void Preferences::setAlternatingRowColors(bool b)
+void Preferences::setAlternatingRowColors(const bool b)
 {
     setValue("Preferences/General/AlternatingRowColors", b);
 }
@@ -144,7 +144,7 @@ bool Preferences::getHideZeroValues() const
     return value("Preferences/General/HideZeroValues", false).toBool();
 }
 
-void Preferences::setHideZeroValues(bool b)
+void Preferences::setHideZeroValues(const bool b)
 {
     setValue("Preferences/General/HideZeroValues", b);
 }
@@ -154,7 +154,7 @@ int Preferences::getHideZeroComboValues() const
     return value("Preferences/General/HideZeroComboValues", 0).toInt();
 }
 
-void Preferences::setHideZeroComboValues(int n)
+void Preferences::setHideZeroComboValues(const int n)
 {
     setValue("Preferences/General/HideZeroComboValues", n);
 }
@@ -167,7 +167,7 @@ bool Preferences::systrayIntegration() const
     return value("Preferences/General/SystrayEnabled", true).toBool();
 }
 
-void Preferences::setSystrayIntegration(bool enabled)
+void Preferences::setSystrayIntegration(const bool enabled)
 {
     setValue("Preferences/General/SystrayEnabled", enabled);
 }
@@ -177,7 +177,7 @@ bool Preferences::minimizeToTray() const
     return value("Preferences/General/MinimizeToTray", false).toBool();
 }
 
-void Preferences::setMinimizeToTray(bool b)
+void Preferences::setMinimizeToTray(const bool b)
 {
     setValue("Preferences/General/MinimizeToTray", b);
 }
@@ -187,7 +187,7 @@ bool Preferences::minimizeToTrayNotified() const
     return value("Preferences/General/MinimizeToTrayNotified", false).toBool();
 }
 
-void Preferences::setMinimizeToTrayNotified(bool b)
+void Preferences::setMinimizeToTrayNotified(const bool b)
 {
     setValue("Preferences/General/MinimizeToTrayNotified", b);
 }
@@ -197,7 +197,7 @@ bool Preferences::closeToTray() const
     return value("Preferences/General/CloseToTray", true).toBool();
 }
 
-void Preferences::setCloseToTray(bool b)
+void Preferences::setCloseToTray(const bool b)
 {
     setValue("Preferences/General/CloseToTray", b);
 }
@@ -207,7 +207,7 @@ bool Preferences::closeToTrayNotified() const
     return value("Preferences/General/CloseToTrayNotified", false).toBool();
 }
 
-void Preferences::setCloseToTrayNotified(bool b)
+void Preferences::setCloseToTrayNotified(const bool b)
 {
     setValue("Preferences/General/CloseToTrayNotified", b);
 }
@@ -218,7 +218,7 @@ bool Preferences::isToolbarDisplayed() const
     return value("Preferences/General/ToolbarDisplayed", true).toBool();
 }
 
-void Preferences::setToolbarDisplayed(bool displayed)
+void Preferences::setToolbarDisplayed(const bool displayed)
 {
     setValue("Preferences/General/ToolbarDisplayed", displayed);
 }
@@ -228,7 +228,7 @@ bool Preferences::isStatusbarDisplayed() const
     return value("Preferences/General/StatusbarDisplayed", true).toBool();
 }
 
-void Preferences::setStatusbarDisplayed(bool displayed)
+void Preferences::setStatusbarDisplayed(const bool displayed)
 {
     setValue("Preferences/General/StatusbarDisplayed", displayed);
 }
@@ -238,7 +238,7 @@ bool Preferences::startMinimized() const
     return value("Preferences/General/StartMinimized", false).toBool();
 }
 
-void Preferences::setStartMinimized(bool b)
+void Preferences::setStartMinimized(const bool b)
 {
     setValue("Preferences/General/StartMinimized", b);
 }
@@ -248,7 +248,7 @@ bool Preferences::isSplashScreenDisabled() const
     return value("Preferences/General/NoSplashScreen", true).toBool();
 }
 
-void Preferences::setSplashScreenDisabled(bool b)
+void Preferences::setSplashScreenDisabled(const bool b)
 {
     setValue("Preferences/General/NoSplashScreen", b);
 }
@@ -259,7 +259,7 @@ bool Preferences::preventFromSuspendWhenDownloading() const
     return value("Preferences/General/PreventFromSuspendWhenDownloading", false).toBool();
 }
 
-void Preferences::setPreventFromSuspendWhenDownloading(bool b)
+void Preferences::setPreventFromSuspendWhenDownloading(const bool b)
 {
     setValue("Preferences/General/PreventFromSuspendWhenDownloading", b);
 }
@@ -269,7 +269,7 @@ bool Preferences::preventFromSuspendWhenSeeding() const
     return value("Preferences/General/PreventFromSuspendWhenSeeding", false).toBool();
 }
 
-void Preferences::setPreventFromSuspendWhenSeeding(bool b)
+void Preferences::setPreventFromSuspendWhenSeeding(const bool b)
 {
     setValue("Preferences/General/PreventFromSuspendWhenSeeding", b);
 }
@@ -281,7 +281,7 @@ bool Preferences::WinStartup() const
     return settings.contains("qBittorrent");
 }
 
-void Preferences::setWinStartup(bool b)
+void Preferences::setWinStartup(const bool b)
 {
     QSettings settings("HKEY_CURRENT_USER\\Software\\Microsoft\\Windows\\CurrentVersion\\Run", QSettings::NativeFormat);
     if (b) {
@@ -331,7 +331,7 @@ bool Preferences::isMailNotificationEnabled() const
     return value("Preferences/MailNotification/enabled", false).toBool();
 }
 
-void Preferences::setMailNotificationEnabled(bool enabled)
+void Preferences::setMailNotificationEnabled(const bool enabled)
 {
     setValue("Preferences/MailNotification/enabled", enabled);
 }
@@ -371,7 +371,7 @@ bool Preferences::getMailNotificationSMTPSSL() const
     return value("Preferences/MailNotification/req_ssl", false).toBool();
 }
 
-void Preferences::setMailNotificationSMTPSSL(bool use)
+void Preferences::setMailNotificationSMTPSSL(const bool use)
 {
     setValue("Preferences/MailNotification/req_ssl", use);
 }
@@ -381,7 +381,7 @@ bool Preferences::getMailNotificationSMTPAuth() const
     return value("Preferences/MailNotification/req_auth", false).toBool();
 }
 
-void Preferences::setMailNotificationSMTPAuth(bool use)
+void Preferences::setMailNotificationSMTPAuth(const bool use)
 {
     setValue("Preferences/MailNotification/req_auth", use);
 }
@@ -411,7 +411,7 @@ int Preferences::getActionOnDblClOnTorrentDl() const
     return value("Preferences/Downloads/DblClOnTorDl", 0).toInt();
 }
 
-void Preferences::setActionOnDblClOnTorrentDl(int act)
+void Preferences::setActionOnDblClOnTorrentDl(const int act)
 {
     setValue("Preferences/Downloads/DblClOnTorDl", act);
 }
@@ -421,7 +421,7 @@ int Preferences::getActionOnDblClOnTorrentFn() const
     return value("Preferences/Downloads/DblClOnTorFn", 1).toInt();
 }
 
-void Preferences::setActionOnDblClOnTorrentFn(int act)
+void Preferences::setActionOnDblClOnTorrentFn(const int act)
 {
     setValue("Preferences/Downloads/DblClOnTorFn", act);
 }
@@ -451,7 +451,7 @@ SchedulerDays Preferences::getSchedulerDays() const
     return static_cast<SchedulerDays>(value("Preferences/Scheduler/days", EVERY_DAY).toInt());
 }
 
-void Preferences::setSchedulerDays(SchedulerDays days)
+void Preferences::setSchedulerDays(const SchedulerDays days)
 {
     setValue("Preferences/Scheduler/days", static_cast<int>(days));
 }
@@ -462,7 +462,7 @@ bool Preferences::isSearchEnabled() const
     return value("Preferences/Search/SearchEnabled", false).toBool();
 }
 
-void Preferences::setSearchEnabled(bool enabled)
+void Preferences::setSearchEnabled(const bool enabled)
 {
     setValue("Preferences/Search/SearchEnabled", enabled);
 }
@@ -476,7 +476,7 @@ bool Preferences::isWebUiEnabled() const
 #endif
 }
 
-void Preferences::setWebUiEnabled(bool enabled)
+void Preferences::setWebUiEnabled(const bool enabled)
 {
     setValue("Preferences/WebUI/Enabled", enabled);
 }
@@ -486,7 +486,7 @@ bool Preferences::isWebUiLocalAuthEnabled() const
     return value("Preferences/WebUI/LocalHostAuth", true).toBool();
 }
 
-void Preferences::setWebUiLocalAuthEnabled(bool enabled)
+void Preferences::setWebUiLocalAuthEnabled(const bool enabled)
 {
     setValue("Preferences/WebUI/LocalHostAuth", enabled);
 }
@@ -496,7 +496,7 @@ bool Preferences::isWebUiAuthSubnetWhitelistEnabled() const
     return value("Preferences/WebUI/AuthSubnetWhitelistEnabled", false).toBool();
 }
 
-void Preferences::setWebUiAuthSubnetWhitelistEnabled(bool enabled)
+void Preferences::setWebUiAuthSubnetWhitelistEnabled(const bool enabled)
 {
     setValue("Preferences/WebUI/AuthSubnetWhitelistEnabled", enabled);
 }
@@ -552,7 +552,7 @@ quint16 Preferences::getWebUiPort() const
     return value("Preferences/WebUI/Port", 8080).toInt();
 }
 
-void Preferences::setWebUiPort(quint16 port)
+void Preferences::setWebUiPort(const quint16 port)
 {
     setValue("Preferences/WebUI/Port", port);
 }
@@ -566,7 +566,7 @@ bool Preferences::useUPnPForWebUIPort() const
 #endif
 }
 
-void Preferences::setUPnPForWebUIPort(bool enabled)
+void Preferences::setUPnPForWebUIPort(const bool enabled)
 {
     setValue("Preferences/WebUI/UseUPnP", enabled);
 }
@@ -598,7 +598,7 @@ bool Preferences::isWebUiClickjackingProtectionEnabled() const
     return value("Preferences/WebUI/ClickjackingProtection", true).toBool();
 }
 
-void Preferences::setWebUiClickjackingProtectionEnabled(bool enabled)
+void Preferences::setWebUiClickjackingProtectionEnabled(const bool enabled)
 {
     setValue("Preferences/WebUI/ClickjackingProtection", enabled);
 }
@@ -608,7 +608,7 @@ bool Preferences::isWebUiCSRFProtectionEnabled() const
     return value("Preferences/WebUI/CSRFProtection", true).toBool();
 }
 
-void Preferences::setWebUiCSRFProtectionEnabled(bool enabled)
+void Preferences::setWebUiCSRFProtectionEnabled(const bool enabled)
 {
     setValue("Preferences/WebUI/CSRFProtection", enabled);
 }
@@ -628,7 +628,7 @@ bool Preferences::isWebUiHttpsEnabled() const
     return value("Preferences/WebUI/HTTPS/Enabled", false).toBool();
 }
 
-void Preferences::setWebUiHttpsEnabled(bool enabled)
+void Preferences::setWebUiHttpsEnabled(const bool enabled)
 {
     setValue("Preferences/WebUI/HTTPS/Enabled", enabled);
 }
@@ -658,7 +658,7 @@ bool Preferences::isAltWebUiEnabled() const
     return value("Preferences/WebUI/AlternativeUIEnabled", false).toBool();
 }
 
-void Preferences::setAltWebUiEnabled(bool enabled)
+void Preferences::setAltWebUiEnabled(const bool enabled)
 {
     setValue("Preferences/WebUI/AlternativeUIEnabled", enabled);
 }
@@ -678,7 +678,7 @@ bool Preferences::isDynDNSEnabled() const
     return value("Preferences/DynDNS/Enabled", false).toBool();
 }
 
-void Preferences::setDynDNSEnabled(bool enabled)
+void Preferences::setDynDNSEnabled(const bool enabled)
 {
     setValue("Preferences/DynDNS/Enabled", enabled);
 }
@@ -688,7 +688,7 @@ DNS::Service Preferences::getDynDNSService() const
     return DNS::Service(value("Preferences/DynDNS/Service", DNS::DYNDNS).toInt());
 }
 
-void Preferences::setDynDNSService(int service)
+void Preferences::setDynDNSService(const int service)
 {
     setValue("Preferences/DynDNS/Service", service);
 }
@@ -739,7 +739,7 @@ bool Preferences::isUILocked() const
     return value("Locking/locked", false).toBool();
 }
 
-void Preferences::setUILocked(bool locked)
+void Preferences::setUILocked(const bool locked)
 {
     return setValue("Locking/locked", locked);
 }
@@ -749,7 +749,7 @@ bool Preferences::isAutoRunEnabled() const
     return value("AutoRun/enabled", false).toBool();
 }
 
-void Preferences::setAutoRunEnabled(bool enabled)
+void Preferences::setAutoRunEnabled(const bool enabled)
 {
     return setValue("AutoRun/enabled", enabled);
 }
@@ -769,7 +769,7 @@ bool Preferences::shutdownWhenDownloadsComplete() const
     return value("Preferences/Downloads/AutoShutDownOnCompletion", false).toBool();
 }
 
-void Preferences::setShutdownWhenDownloadsComplete(bool shutdown)
+void Preferences::setShutdownWhenDownloadsComplete(const bool shutdown)
 {
     setValue("Preferences/Downloads/AutoShutDownOnCompletion", shutdown);
 }
@@ -779,7 +779,7 @@ bool Preferences::suspendWhenDownloadsComplete() const
     return value("Preferences/Downloads/AutoSuspendOnCompletion", false).toBool();
 }
 
-void Preferences::setSuspendWhenDownloadsComplete(bool suspend)
+void Preferences::setSuspendWhenDownloadsComplete(const bool suspend)
 {
     setValue("Preferences/Downloads/AutoSuspendOnCompletion", suspend);
 }
@@ -789,7 +789,7 @@ bool Preferences::hibernateWhenDownloadsComplete() const
     return value("Preferences/Downloads/AutoHibernateOnCompletion", false).toBool();
 }
 
-void Preferences::setHibernateWhenDownloadsComplete(bool hibernate)
+void Preferences::setHibernateWhenDownloadsComplete(const bool hibernate)
 {
     setValue("Preferences/Downloads/AutoHibernateOnCompletion", hibernate);
 }
@@ -799,7 +799,7 @@ bool Preferences::shutdownqBTWhenDownloadsComplete() const
     return value("Preferences/Downloads/AutoShutDownqBTOnCompletion", false).toBool();
 }
 
-void Preferences::setShutdownqBTWhenDownloadsComplete(bool shutdown)
+void Preferences::setShutdownqBTWhenDownloadsComplete(const bool shutdown)
 {
     setValue("Preferences/Downloads/AutoShutDownqBTOnCompletion", shutdown);
 }
@@ -809,7 +809,7 @@ bool Preferences::dontConfirmAutoExit() const
     return value("ShutdownConfirmDlg/DontConfirmAutoExit", false).toBool();
 }
 
-void Preferences::setDontConfirmAutoExit(bool dontConfirmAutoExit)
+void Preferences::setDontConfirmAutoExit(const bool dontConfirmAutoExit)
 {
     setValue("ShutdownConfirmDlg/DontConfirmAutoExit", dontConfirmAutoExit);
 }
@@ -819,7 +819,7 @@ bool Preferences::recheckTorrentsOnCompletion() const
     return value("Preferences/Advanced/RecheckOnCompletion", false).toBool();
 }
 
-void Preferences::recheckTorrentsOnCompletion(bool recheck)
+void Preferences::recheckTorrentsOnCompletion(const bool recheck)
 {
     setValue("Preferences/Advanced/RecheckOnCompletion", recheck);
 }
@@ -829,7 +829,7 @@ bool Preferences::resolvePeerCountries() const
     return value("Preferences/Connection/ResolvePeerCountries", true).toBool();
 }
 
-void Preferences::resolvePeerCountries(bool resolve)
+void Preferences::resolvePeerCountries(const bool resolve)
 {
     setValue("Preferences/Connection/ResolvePeerCountries", resolve);
 }
@@ -839,7 +839,7 @@ bool Preferences::resolvePeerHostNames() const
     return value("Preferences/Connection/ResolvePeerHostNames", false).toBool();
 }
 
-void Preferences::resolvePeerHostNames(bool resolve)
+void Preferences::resolvePeerHostNames(const bool resolve)
 {
     setValue("Preferences/Connection/ResolvePeerHostNames", resolve);
 }
@@ -850,7 +850,7 @@ bool Preferences::useSystemIconTheme() const
     return value("Preferences/Advanced/useSystemIconTheme", true).toBool();
 }
 
-void Preferences::useSystemIconTheme(bool enabled)
+void Preferences::useSystemIconTheme(const bool enabled)
 {
     setValue("Preferences/Advanced/useSystemIconTheme", enabled);
 }
@@ -861,7 +861,7 @@ bool Preferences::recursiveDownloadDisabled() const
     return value("Preferences/Advanced/DisableRecursiveDownload", false).toBool();
 }
 
-void Preferences::disableRecursiveDownload(bool disable)
+void Preferences::disableRecursiveDownload(const bool disable)
 {
     setValue("Preferences/Advanced/DisableRecursiveDownload", disable);
 }
@@ -872,14 +872,14 @@ bool Preferences::neverCheckFileAssoc() const
     return value("Preferences/Win32/NeverCheckFileAssocation", false).toBool();
 }
 
-void Preferences::setNeverCheckFileAssoc(bool check)
+void Preferences::setNeverCheckFileAssoc(const bool check)
 {
     setValue("Preferences/Win32/NeverCheckFileAssocation", check);
 }
 
 bool Preferences::isTorrentFileAssocSet()
 {
-    QSettings settings("HKEY_CURRENT_USER\\Software\\Classes", QSettings::NativeFormat);
+    const QSettings settings("HKEY_CURRENT_USER\\Software\\Classes", QSettings::NativeFormat);
     if (settings.value(".torrent/Default").toString() != "qBittorrent") {
         qDebug(".torrent != qBittorrent");
         return false;
@@ -890,7 +890,7 @@ bool Preferences::isTorrentFileAssocSet()
 
 bool Preferences::isMagnetLinkAssocSet()
 {
-    QSettings settings("HKEY_CURRENT_USER\\Software\\Classes", QSettings::NativeFormat);
+    const QSettings settings("HKEY_CURRENT_USER\\Software\\Classes", QSettings::NativeFormat);
 
     // Check magnet link assoc
     const QString shellCommand = Utils::Fs::toNativePath(settings.value("magnet/shell/open/command/Default", "").toString());
@@ -906,13 +906,13 @@ bool Preferences::isMagnetLinkAssocSet()
     return true;
 }
 
-void Preferences::setTorrentFileAssoc(bool set)
+void Preferences::setTorrentFileAssoc(const bool set)
 {
     QSettings settings("HKEY_CURRENT_USER\\Software\\Classes", QSettings::NativeFormat);
 
     // .Torrent association
     if (set) {
-        QString oldProgId = settings.value(".torrent/Default").toString();
+        const QString oldProgId = settings.value(".torrent/Default").toString();
         if (!oldProgId.isEmpty() && (oldProgId != "qBittorrent"))
             settings.setValue(".torrent/OpenWithProgids/" + oldProgId, "");
         settings.setValue(".torrent/Default", "qBittorrent");
@@ -924,7 +924,7 @@ void Preferences::setTorrentFileAssoc(bool set)
     SHChangeNotify(SHCNE_ASSOCCHANGED, SHCNF_IDLIST, 0, 0);
 }
 
-void Preferences::setMagnetLinkAssoc(bool set)
+void Preferences::setMagnetLinkAssoc(const bool set)
 {
     QSettings settings("HKEY_CURRENT_USER\\Software\\Classes", QSettings::NativeFormat);
 
@@ -951,18 +951,18 @@ void Preferences::setMagnetLinkAssoc(bool set)
 #ifdef Q_OS_MAC
 namespace
 {
-    CFStringRef torrentExtension = CFSTR("torrent");
-    CFStringRef magnetUrlScheme = CFSTR("magnet");
+    const CFStringRef torrentExtension = CFSTR("torrent");
+    const CFStringRef magnetUrlScheme = CFSTR("magnet");
 }
 
 bool Preferences::isTorrentFileAssocSet()
 {
     bool isSet = false;
-    CFStringRef torrentId = UTTypeCreatePreferredIdentifierForTag(kUTTagClassFilenameExtension, torrentExtension, NULL);
+    const CFStringRef torrentId = UTTypeCreatePreferredIdentifierForTag(kUTTagClassFilenameExtension, torrentExtension, NULL);
     if (torrentId != NULL) {
-        CFStringRef defaultHandlerId = LSCopyDefaultRoleHandlerForContentType(torrentId, kLSRolesViewer);
+        const CFStringRef defaultHandlerId = LSCopyDefaultRoleHandlerForContentType(torrentId, kLSRolesViewer);
         if (defaultHandlerId != NULL) {
-            CFStringRef myBundleId = CFBundleGetIdentifier(CFBundleGetMainBundle());
+            const CFStringRef myBundleId = CFBundleGetIdentifier(CFBundleGetMainBundle());
             isSet = CFStringCompare(myBundleId, defaultHandlerId, 0) == kCFCompareEqualTo;
             CFRelease(defaultHandlerId);
         }
@@ -974,9 +974,9 @@ bool Preferences::isTorrentFileAssocSet()
 bool Preferences::isMagnetLinkAssocSet()
 {
     bool isSet = false;
-    CFStringRef defaultHandlerId = LSCopyDefaultHandlerForURLScheme(magnetUrlScheme);
+    const CFStringRef defaultHandlerId = LSCopyDefaultHandlerForURLScheme(magnetUrlScheme);
     if (defaultHandlerId != NULL) {
-        CFStringRef myBundleId = CFBundleGetIdentifier(CFBundleGetMainBundle());
+        const CFStringRef myBundleId = CFBundleGetIdentifier(CFBundleGetMainBundle());
         isSet = CFStringCompare(myBundleId, defaultHandlerId, 0) == kCFCompareEqualTo;
         CFRelease(defaultHandlerId);
     }
@@ -987,9 +987,9 @@ void Preferences::setTorrentFileAssoc()
 {
     if (isTorrentFileAssocSet())
         return;
-    CFStringRef torrentId = UTTypeCreatePreferredIdentifierForTag(kUTTagClassFilenameExtension, torrentExtension, NULL);
+    const CFStringRef torrentId = UTTypeCreatePreferredIdentifierForTag(kUTTagClassFilenameExtension, torrentExtension, NULL);
     if (torrentId != NULL) {
-        CFStringRef myBundleId = CFBundleGetIdentifier(CFBundleGetMainBundle());
+        const CFStringRef myBundleId = CFBundleGetIdentifier(CFBundleGetMainBundle());
         LSSetDefaultRoleHandlerForContentType(torrentId, kLSRolesViewer, myBundleId);
         CFRelease(torrentId);
     }
@@ -999,7 +999,7 @@ void Preferences::setMagnetLinkAssoc()
 {
     if (isMagnetLinkAssocSet())
         return;
-    CFStringRef myBundleId = CFBundleGetIdentifier(CFBundleGetMainBundle());
+    const CFStringRef myBundleId = CFBundleGetIdentifier(CFBundleGetMainBundle());
     LSSetDefaultHandlerForURLScheme(magnetUrlScheme, myBundleId);
 }
 #endif // Q_OS_MAC
@@ -1009,7 +1009,7 @@ int Preferences::getTrackerPort() const
     return value("Preferences/Advanced/trackerPort", 9000).toInt();
 }
 
-void Preferences::setTrackerPort(int port)
+void Preferences::setTrackerPort(const int port)
 {
     setValue("Preferences/Advanced/trackerPort", port);
 }
@@ -1020,7 +1020,7 @@ bool Preferences::isUpdateCheckEnabled() const
     return value("Preferences/Advanced/updateCheck", true).toBool();
 }
 
-void Preferences::setUpdateCheckEnabled(bool enabled)
+void Preferences::setUpdateCheckEnabled(const bool enabled)
 {
     setValue("Preferences/Advanced/updateCheck", enabled);
 }
@@ -1031,7 +1031,7 @@ bool Preferences::confirmTorrentDeletion() const
     return value("Preferences/Advanced/confirmTorrentDeletion", true).toBool();
 }
 
-void Preferences::setConfirmTorrentDeletion(bool enabled)
+void Preferences::setConfirmTorrentDeletion(const bool enabled)
 {
     setValue("Preferences/Advanced/confirmTorrentDeletion", enabled);
 }
@@ -1041,7 +1041,7 @@ bool Preferences::confirmTorrentRecheck() const
     return value("Preferences/Advanced/confirmTorrentRecheck", true).toBool();
 }
 
-void Preferences::setConfirmTorrentRecheck(bool enabled)
+void Preferences::setConfirmTorrentRecheck(const bool enabled)
 {
     setValue("Preferences/Advanced/confirmTorrentRecheck", enabled);
 }
@@ -1051,7 +1051,7 @@ bool Preferences::confirmRemoveAllTags() const
     return value("Preferences/Advanced/confirmRemoveAllTags", true).toBool();
 }
 
-void Preferences::setConfirmRemoveAllTags(bool enabled)
+void Preferences::setConfirmRemoveAllTags(const bool enabled)
 {
     setValue("Preferences/Advanced/confirmRemoveAllTags", enabled);
 }
@@ -1062,7 +1062,7 @@ TrayIcon::Style Preferences::trayIconStyle() const
     return TrayIcon::Style(value("Preferences/Advanced/TrayIconStyle", TrayIcon::NORMAL).toInt());
 }
 
-void Preferences::setTrayIconStyle(TrayIcon::Style style)
+void Preferences::setTrayIconStyle(const TrayIcon::Style style)
 {
     setValue("Preferences/Advanced/TrayIconStyle", style);
 }
@@ -1186,7 +1186,7 @@ int Preferences::getPropCurTab() const
     return value("TorrentProperties/CurrentTab", -1).toInt();
 }
 
-void Preferences::setPropCurTab(const int &tab)
+void Preferences::setPropCurTab(const int tab)
 {
     setValue("TorrentProperties/CurrentTab", tab);
 }
@@ -1356,7 +1356,7 @@ int Preferences::getTransSelFilter() const
     return value("TransferListFilters/selectedFilterIndex", 0).toInt();
 }
 
-void Preferences::setTransSelFilter(const int &index)
+void Preferences::setTransSelFilter(const int index)
 {
     setValue("TransferListFilters/selectedFilterIndex", index);
 }
@@ -1426,7 +1426,7 @@ bool Preferences::isSpeedWidgetEnabled() const
     return value("SpeedWidget/Enabled", true).toBool();
 }
 
-void Preferences::setSpeedWidgetEnabled(bool enabled)
+void Preferences::setSpeedWidgetEnabled(const bool enabled)
 {
     setValue("SpeedWidget/Enabled", enabled);
 }
@@ -1441,13 +1441,13 @@ void Preferences::setSpeedWidgetPeriod(const int period)
     setValue("SpeedWidget/period", period);
 }
 
-bool Preferences::getSpeedWidgetGraphEnable(int id) const
+bool Preferences::getSpeedWidgetGraphEnable(const int id) const
 {
     // UP and DOWN graphs enabled by default
     return value("SpeedWidget/graph_enable_" + QString::number(id), (id == 0 || id == 1)).toBool();
 }
 
-void Preferences::setSpeedWidgetGraphEnable(int id, const bool enable)
+void Preferences::setSpeedWidgetGraphEnable(const int id, const bool enable)
 {
     setValue("SpeedWidget/graph_enable_" + QString::number(id), enable);
 }
diff --git a/src/base/preferences.h b/src/base/preferences.h
index d80eaf19b..d8aaab2e2 100644
--- a/src/base/preferences.h
+++ b/src/base/preferences.h
@@ -83,7 +83,7 @@ class Preferences : public QObject
 
     Preferences();
 
-    const QVariant value(const QString &key, const QVariant &defaultValue = QVariant()) const;
+    const QVariant value(const QString &key, const QVariant &defaultValue = {}) const;
     void setValue(const QString &key, const QVariant &value);
 
     static Preferences *m_instance;
@@ -303,7 +303,7 @@ public:
     QString getDNSLastIP() const;
     void setDNSLastIP(const QString &ip);
     bool getAcceptedLegal() const;
-    void setAcceptedLegal(const bool accepted);
+    void setAcceptedLegal(bool accepted);
     QByteArray getMainGeometry() const;
     void setMainGeometry(const QByteArray &geometry);
     QByteArray getMainVSplitterState() const;
@@ -321,9 +321,9 @@ public:
     QByteArray getPropFileListState() const;
     void setPropFileListState(const QByteArray &state);
     int getPropCurTab() const;
-    void setPropCurTab(const int &tab);
+    void setPropCurTab(int tab);
     bool getPropVisible() const;
-    void setPropVisible(const bool visible);
+    void setPropVisible(bool visible);
     QByteArray getPropTrackerListState() const;
     void setPropTrackerListState(const QByteArray &state);
     QSize getRssGeometrySize() const;
@@ -351,17 +351,17 @@ public:
     bool getTagFilterState() const;
     bool getTrackerFilterState() const;
     int getTransSelFilter() const;
-    void setTransSelFilter(const int &index);
+    void setTransSelFilter(int index);
     QByteArray getTransHeaderState() const;
     void setTransHeaderState(const QByteArray &state);
     bool getRegexAsFilteringPatternForTransferList() const;
     void setRegexAsFilteringPatternForTransferList(bool checked);
     int getToolbarTextPosition() const;
-    void setToolbarTextPosition(const int position);
+    void setToolbarTextPosition(int position);
 
     // From old RssSettings class
     bool isRSSWidgetEnabled() const;
-    void setRSSWidgetVisible(const bool enabled);
+    void setRSSWidgetVisible(bool enabled);
 
     // Network
     QList<QNetworkCookie> getNetworkCookies() const;
@@ -371,9 +371,9 @@ public:
     bool isSpeedWidgetEnabled() const;
     void setSpeedWidgetEnabled(bool enabled);
     int getSpeedWidgetPeriod() const;
-    void setSpeedWidgetPeriod(const int period);
+    void setSpeedWidgetPeriod(int period);
     bool getSpeedWidgetGraphEnable(int id) const;
-    void setSpeedWidgetGraphEnable(int id, const bool enable);
+    void setSpeedWidgetGraphEnable(int id, bool enable);
 
 public slots:
     void setStatusFilterState(bool checked);
diff --git a/src/base/private/profile_p.cpp b/src/base/private/profile_p.cpp
index 0addacddc..656beeebf 100644
--- a/src/base/private/profile_p.cpp
+++ b/src/base/private/profile_p.cpp
@@ -103,7 +103,7 @@ SettingsPtr Private::DefaultProfile::applicationSettings(const QString &name) co
 #endif
 }
 
-QString Private::DefaultProfile::locationWithConfigurationName(QStandardPaths::StandardLocation location) const
+QString Private::DefaultProfile::locationWithConfigurationName(const QStandardPaths::StandardLocation location) const
 {
     return QStandardPaths::writableLocation(location) + configurationSuffix();
 }
@@ -174,9 +174,9 @@ QString Private::Converter::toPortablePath(const QString &path) const
 
 #ifdef Q_OS_WIN
     if (QDir::isAbsolutePath(path)) {
-        QChar driveLeter = path[0].toUpper();
-        QChar baseDriveLetter = m_baseDir.path()[0].toUpper();
-        bool onSameDrive = (driveLeter.category() == QChar::Letter_Uppercase) && (driveLeter == baseDriveLetter);
+        const QChar driveLeter = path[0].toUpper();
+        const QChar baseDriveLetter = m_baseDir.path()[0].toUpper();
+        const bool onSameDrive = (driveLeter.category() == QChar::Letter_Uppercase) && (driveLeter == baseDriveLetter);
         if (!onSameDrive)
             return path;
     }
diff --git a/src/base/profile.cpp b/src/base/profile.cpp
index a63e7833e..2b272239b 100644
--- a/src/base/profile.cpp
+++ b/src/base/profile.cpp
@@ -65,7 +65,7 @@ const Profile &Profile::instance()
     return *m_instance;
 }
 
-QString Profile::location(SpecialFolder folder) const
+QString Profile::location(const SpecialFolder folder) const
 {
     QString result;
     switch (folder) {
@@ -98,9 +98,9 @@ SettingsPtr Profile::applicationSettings(const QString &name) const
     return m_profileImpl->applicationSettings(name);
 }
 
-void Profile::ensureDirectoryExists(SpecialFolder folder)
+void Profile::ensureDirectoryExists(const SpecialFolder folder)
 {
-    QString locationPath = location(folder);
+    const QString locationPath = location(folder);
     if (!locationPath.isEmpty() && !QDir().mkpath(locationPath))
         qFatal("Could not create required directory '%s'", qUtf8Printable(locationPath));
 }
diff --git a/src/base/rss/private/rss_parser.cpp b/src/base/rss/private/rss_parser.cpp
index 75a62ab54..f1777f2e7 100644
--- a/src/base/rss/private/rss_parser.cpp
+++ b/src/base/rss/private/rss_parser.cpp
@@ -396,8 +396,8 @@ namespace
         if (!str.indexOf(rx)) {
             // Check that if date has '-' separators, both separators are '-'.
             parts = rx.capturedTexts();
-            bool h1 = (parts[3] == QLatin1String("-"));
-            bool h2 = (parts[5] == QLatin1String("-"));
+            const bool h1 = (parts[3] == QLatin1String("-"));
+            const bool h2 = (parts[5] == QLatin1String("-"));
             if (h1 != h2)
                 return QDateTime::currentDateTime();
         }
@@ -431,7 +431,7 @@ namespace
                 return QDateTime::currentDateTime();
         }
 
-        bool leapSecond = (second == 60);
+        const bool leapSecond = (second == 60);
         if (leapSecond)
             second = 59;   // apparently a leap second - validate below, once time zone is known
         int month = 0;
@@ -447,7 +447,7 @@ namespace
         //       if (month >= 12 || dayOfWeek >= 7
         //       ||  (dayOfWeek < 0  &&  format == RFCDateDay))
         //         return QDateTime;
-        int i = parts[nyear].size();
+        const int i = parts[nyear].size();
         if (i < 4) {
             // It's an obsolete year specification with less than 4 digits
             year += ((i == 2) && (year < 50)) ? 2000 : 1900;
@@ -462,7 +462,7 @@ namespace
                 // It's a UTC offset ±hhmm
                 parts = rx.capturedTexts();
                 offset = parts[2].toInt(&ok[0]) * 3600;
-                int offsetMin = parts[3].toInt(&ok[1]);
+                const int offsetMin = parts[3].toInt(&ok[1]);
                 if (!ok[0] || !ok[1] || offsetMin > 59)
                     return {};
                 offset += offsetMin * 60;
@@ -472,7 +472,7 @@ namespace
             }
             else {
                 // Check for an obsolete time zone name
-                QByteArray zone = parts[10].toLatin1();
+                const QByteArray zone = parts[10].toLatin1();
                 if ((zone.length() == 1) && (isalpha(zone[0])) && (toupper(zone[0]) != 'J')) {
                     negOffset = true;    // military zone: RFC 2822 treats as '-0000'
                 }
@@ -502,11 +502,11 @@ namespace
             }
         }
 
-        QDate qDate(year, month + 1, day);   // convert date, and check for out-of-range
+        const QDate qDate(year, month + 1, day);   // convert date, and check for out-of-range
         if (!qDate.isValid())
             return QDateTime::currentDateTime();
 
-        QTime qTime(hour, minute, second);
+        const QTime qTime(hour, minute, second);
         QDateTime result(qDate, qTime, Qt::UTC);
         if (offset)
             result = result.addSecs(-offset);
@@ -528,7 +528,7 @@ using namespace RSS::Private;
 
 const int ParsingResultTypeId = qRegisterMetaType<ParsingResult>();
 
-Parser::Parser(QString lastBuildDate)
+Parser::Parser(const QString lastBuildDate)
 {
     m_result.lastBuildDate = lastBuildDate;
 }
@@ -642,7 +642,7 @@ void Parser::parseRSSChannel(QXmlStreamReader &xml)
                 m_result.title = xml.readElementText();
             }
             else if (xml.name() == QLatin1String("lastBuildDate")) {
-                QString lastBuildDate = xml.readElementText();
+                const QString lastBuildDate = xml.readElementText();
                 if (!lastBuildDate.isEmpty()) {
                     if (m_result.lastBuildDate == lastBuildDate) {
                         qDebug() << "The RSS feed has not changed since last time, aborting parsing.";
@@ -675,7 +675,7 @@ void Parser::parseAtomArticle(QXmlStreamReader &xml)
                 article[Article::KeyTitle] = xml.readElementText().trimmed();
             }
             else if (name == QLatin1String("link")) {
-                QString link = (xml.attributes().isEmpty()
+                const QString link = (xml.attributes().isEmpty()
                                 ? xml.readElementText().trimmed()
                                 : xml.attributes().value(QLatin1String("href")).toString());
 
@@ -696,7 +696,7 @@ void Parser::parseAtomArticle(QXmlStreamReader &xml)
 
                 // Try to also parse broken articles, which don't use html '&' escapes
                 // Actually works great for non-broken content too
-                QString feedText = xml.readElementText(QXmlStreamReader::IncludeChildElements).trimmed();
+                const QString feedText = xml.readElementText(QXmlStreamReader::IncludeChildElements).trimmed();
                 if (!feedText.isEmpty()) {
                     article[Article::KeyDescription] = feedText;
                     doubleContent = true;
@@ -704,7 +704,7 @@ void Parser::parseAtomArticle(QXmlStreamReader &xml)
             }
             else if (name == QLatin1String("updated")) {
                 // ATOM uses standard compliant date, don't do fancy stuff
-                QDateTime articleDate = QDateTime::fromString(xml.readElementText().trimmed(), Qt::ISODate);
+                const QDateTime articleDate = QDateTime::fromString(xml.readElementText().trimmed(), Qt::ISODate);
                 article[Article::KeyDate] = (articleDate.isValid() ? articleDate : QDateTime::currentDateTime());
             }
             else if (name == QLatin1String("author")) {
@@ -739,7 +739,7 @@ void Parser::parseAtomChannel(QXmlStreamReader &xml)
                 m_result.title = xml.readElementText();
             }
             else if (xml.name() == QLatin1String("updated")) {
-                QString lastBuildDate = xml.readElementText();
+                const QString lastBuildDate = xml.readElementText();
                 if (!lastBuildDate.isEmpty()) {
                     if (m_result.lastBuildDate == lastBuildDate) {
                         qDebug() << "The RSS feed has not changed since last time, aborting parsing.";
diff --git a/src/base/rss/rss_article.cpp b/src/base/rss/rss_article.cpp
index 11ced4e4b..9e88adc3b 100644
--- a/src/base/rss/rss_article.cpp
+++ b/src/base/rss/rss_article.cpp
@@ -142,7 +142,7 @@ QJsonObject Article::toJsonObject() const
     return jsonObj;
 }
 
-bool Article::articleDateRecentThan(Article *article, const QDateTime &date)
+bool Article::articleDateRecentThan(const Article *article, const QDateTime &date)
 {
     return article->date() > date;
 }
diff --git a/src/base/rss/rss_article.h b/src/base/rss/rss_article.h
index 681b1dfa2..e070f0850 100644
--- a/src/base/rss/rss_article.h
+++ b/src/base/rss/rss_article.h
@@ -74,7 +74,7 @@ namespace RSS
 
         QJsonObject toJsonObject() const;
 
-        static bool articleDateRecentThan(Article *article, const QDateTime &date);
+        static bool articleDateRecentThan(const Article *article, const QDateTime &date);
 
     signals:
         void read(Article *article = nullptr);
diff --git a/src/base/rss/rss_autodownloader.cpp b/src/base/rss/rss_autodownloader.cpp
index 187c78702..4a8609b3f 100644
--- a/src/base/rss/rss_autodownloader.cpp
+++ b/src/base/rss/rss_autodownloader.cpp
@@ -73,7 +73,7 @@ namespace
     QVector<RSS::AutoDownloadRule> rulesFromJSON(const QByteArray &jsonData)
     {
         QJsonParseError jsonError;
-        QJsonDocument jsonDoc = QJsonDocument::fromJson(jsonData, &jsonError);
+        const QJsonDocument jsonDoc = QJsonDocument::fromJson(jsonData, &jsonError);
         if (jsonError.error != QJsonParseError::NoError)
             throw RSS::ParsingError(jsonError.errorString());
 
@@ -227,7 +227,7 @@ QByteArray AutoDownloader::exportRules(AutoDownloader::RulesFileFormat format) c
     }
 }
 
-void AutoDownloader::importRules(const QByteArray &data, AutoDownloader::RulesFileFormat format)
+void AutoDownloader::importRules(const QByteArray &data, const AutoDownloader::RulesFileFormat format)
 {
     switch (format) {
     case RulesFileFormat::Legacy:
@@ -333,7 +333,7 @@ void AutoDownloader::process()
 
 void AutoDownloader::handleTorrentDownloadFinished(const QString &url)
 {
-    auto job = m_waitingJobs.take(url);
+    const auto job = m_waitingJobs.take(url);
     if (!job) return;
 
     if (Feed *feed = Session::instance()->feedByURL(job->feedURL))
@@ -347,7 +347,7 @@ void AutoDownloader::handleTorrentDownloadFailed(const QString &url)
     // TODO: Re-schedule job here.
 }
 
-void AutoDownloader::handleNewArticle(Article *article)
+void AutoDownloader::handleNewArticle(const Article *article)
 {
     if (!article->isRead() && !article->torrentUrl().isEmpty())
         addJobForArticle(article);
@@ -358,7 +358,7 @@ void AutoDownloader::setRule_impl(const AutoDownloadRule &rule)
     m_rules.insert(rule.name(), rule);
 }
 
-void AutoDownloader::addJobForArticle(Article *article)
+void AutoDownloader::addJobForArticle(const Article *article)
 {
     const QString torrentURL = article->torrentUrl();
     if (m_waitingJobs.contains(torrentURL)) return;
@@ -387,7 +387,7 @@ void AutoDownloader::processJob(const QSharedPointer<ProcessingJob> &job)
         params.addPaused = rule.addPaused();
         if (!rule.savePath().isEmpty())
             params.useAutoTMM = TriStateBool::False;
-        auto torrentURL = job->articleData.value(Article::KeyTorrentURL).toString();
+        const auto torrentURL = job->articleData.value(Article::KeyTorrentURL).toString();
         BitTorrent::Session::instance()->addTorrent(torrentURL, params);
 
         if (BitTorrent::MagnetUri(torrentURL).isValid()) {
@@ -434,10 +434,10 @@ void AutoDownloader::loadRules(const QByteArray &data)
 
 void AutoDownloader::loadRulesLegacy()
 {
-    SettingsPtr settings = Profile::instance().applicationSettings(QStringLiteral("qBittorrent-rss"));
+    const SettingsPtr settings = Profile::instance().applicationSettings(QStringLiteral("qBittorrent-rss"));
     const QVariantHash rules = settings->value(QStringLiteral("download_rules")).toHash();
     for (const QVariant &ruleVar : rules) {
-        auto rule = AutoDownloadRule::fromLegacyDict(ruleVar.toHash());
+        const auto rule = AutoDownloadRule::fromLegacyDict(ruleVar.toHash());
         if (!rule.name().isEmpty())
             insertRule(rule);
     }
@@ -485,7 +485,7 @@ void AutoDownloader::startProcessing()
     connect(Session::instance()->rootFolder(), &Folder::newArticle, this, &AutoDownloader::handleNewArticle);
 }
 
-void AutoDownloader::setProcessingEnabled(bool enabled)
+void AutoDownloader::setProcessingEnabled(const bool enabled)
 {
     if (m_processingEnabled != enabled) {
         m_processingEnabled = enabled;
diff --git a/src/base/rss/rss_autodownloader.h b/src/base/rss/rss_autodownloader.h
index 43b908730..91dfe424c 100644
--- a/src/base/rss/rss_autodownloader.h
+++ b/src/base/rss/rss_autodownloader.h
@@ -110,14 +110,14 @@ namespace RSS
         void process();
         void handleTorrentDownloadFinished(const QString &url);
         void handleTorrentDownloadFailed(const QString &url);
-        void handleNewArticle(Article *article);
+        void handleNewArticle(const Article *article);
 
     private:
         void timerEvent(QTimerEvent *event) override;
         void setRule_impl(const AutoDownloadRule &rule);
         void resetProcessingQueue();
         void startProcessing();
-        void addJobForArticle(Article *article);
+        void addJobForArticle(const Article *article);
         void processJob(const QSharedPointer<ProcessingJob> &job);
         void load();
         void loadRules(const QByteArray &data);
diff --git a/src/base/rss/rss_autodownloadrule.cpp b/src/base/rss/rss_autodownloadrule.cpp
index 596bf7d0f..3e6c57566 100644
--- a/src/base/rss/rss_autodownloadrule.cpp
+++ b/src/base/rss/rss_autodownloadrule.cpp
@@ -72,7 +72,7 @@ namespace
         }
     }
 
-    TriStateBool addPausedLegacyToTriStateBool(int val)
+    TriStateBool addPausedLegacyToTriStateBool(const int val)
     {
         switch (val) {
         case 1:  return TriStateBool::True; // always
@@ -163,13 +163,13 @@ QString computeEpisodeName(const QString &article)
 
     QStringList ret;
     for (int i = 1; i <= match.lastCapturedIndex(); ++i) {
-        QString cap = match.captured(i);
+        const QString cap = match.captured(i);
 
         if (cap.isEmpty())
             continue;
 
         bool isInt = false;
-        int x = cap.toInt(&isInt);
+        const int x = cap.toInt(&isInt);
 
         ret.append(isInt ? QString::number(x) : cap);
     }
@@ -189,7 +189,7 @@ AutoDownloadRule::AutoDownloadRule(const AutoDownloadRule &other)
 
 AutoDownloadRule::~AutoDownloadRule() {}
 
-QRegularExpression AutoDownloadRule::cachedRegex(const QString &expression, bool isRegex) const
+QRegularExpression AutoDownloadRule::cachedRegex(const QString &expression, const bool isRegex) const
 {
     // Use a cache of regexes so we don't have to continually recompile - big performance increase.
     // The cache is cleared whenever the regex/wildcard, must or must not contain fields or
@@ -216,7 +216,7 @@ bool AutoDownloadRule::matchesExpression(const QString &articleTitle, const QStr
     }
 
     if (m_dataPtr->useRegex) {
-        QRegularExpression reg(cachedRegex(expression));
+        const QRegularExpression reg(cachedRegex(expression));
         return reg.match(articleTitle).hasMatch();
     }
 
@@ -600,7 +600,7 @@ bool AutoDownloadRule::isEnabled() const
     return m_dataPtr->enabled;
 }
 
-void AutoDownloadRule::setEnabled(bool enable)
+void AutoDownloadRule::setEnabled(const bool enable)
 {
     m_dataPtr->enabled = enable;
 }
@@ -615,7 +615,7 @@ void AutoDownloadRule::setLastMatch(const QDateTime &lastMatch)
     m_dataPtr->lastMatch = lastMatch;
 }
 
-void AutoDownloadRule::setIgnoreDays(int d)
+void AutoDownloadRule::setIgnoreDays(const int d)
 {
     m_dataPtr->ignoreDays = d;
 }
@@ -640,7 +640,7 @@ bool AutoDownloadRule::useSmartFilter() const
     return m_dataPtr->smartFilter;
 }
 
-void AutoDownloadRule::setUseSmartFilter(bool enabled)
+void AutoDownloadRule::setUseSmartFilter(const bool enabled)
 {
     m_dataPtr->smartFilter = enabled;
 }
@@ -650,7 +650,7 @@ bool AutoDownloadRule::useRegex() const
     return m_dataPtr->useRegex;
 }
 
-void AutoDownloadRule::setUseRegex(bool enabled)
+void AutoDownloadRule::setUseRegex(const bool enabled)
 {
     m_dataPtr->useRegex = enabled;
     m_dataPtr->cachedRegexes.clear();
diff --git a/src/base/rss/rss_feed.cpp b/src/base/rss/rss_feed.cpp
index 68afb2eac..21e7bba11 100644
--- a/src/base/rss/rss_feed.cpp
+++ b/src/base/rss/rss_feed.cpp
@@ -108,7 +108,7 @@ QList<Article *> Feed::articles() const
 
 void Feed::markAsRead()
 {
-    auto oldUnreadCount = m_unreadCount;
+    const int oldUnreadCount = m_unreadCount;
     for (Article *article : asConst(m_articles)) {
         if (!article->isRead()) {
             article->disconnect(this);
@@ -176,7 +176,7 @@ Article *Feed::articleByGUID(const QString &guid) const
     return m_articles.value(guid);
 }
 
-void Feed::handleMaxArticlesPerFeedChanged(int n)
+void Feed::handleMaxArticlesPerFeedChanged(const int n)
 {
     while (m_articlesByDate.size() > n)
         removeOldestArticle();
@@ -270,7 +270,7 @@ void Feed::load()
 void Feed::loadArticles(const QByteArray &data)
 {
     QJsonParseError jsonError;
-    QJsonDocument jsonDoc = QJsonDocument::fromJson(data, &jsonError);
+    const QJsonDocument jsonDoc = QJsonDocument::fromJson(data, &jsonError);
     if (jsonError.error != QJsonParseError::NoError) {
         LogMsg(tr("Couldn't parse RSS Session data. Error: %1").arg(jsonError.errorString())
                , Log::WARNING);
@@ -303,7 +303,7 @@ void Feed::loadArticles(const QByteArray &data)
 
 void Feed::loadArticlesLegacy()
 {
-    SettingsPtr qBTRSSFeeds = Profile::instance().applicationSettings(QStringLiteral("qBittorrent-rss-feeds"));
+    const SettingsPtr qBTRSSFeeds = Profile::instance().applicationSettings(QStringLiteral("qBittorrent-rss-feeds"));
     const QVariantHash allOldItems = qBTRSSFeeds->value("old_items").toHash();
 
     for (const QVariant &var : asConst(allOldItems.value(m_url).toList())) {
@@ -348,7 +348,7 @@ bool Feed::addArticle(Article *article)
 
     // Insertion sort
     const int maxArticles = m_session->maxArticlesPerFeed();
-    auto lowerBound = std::lower_bound(m_articlesByDate.begin(), m_articlesByDate.end()
+    const auto lowerBound = std::lower_bound(m_articlesByDate.begin(), m_articlesByDate.end()
                                        , article->date(), Article::articleDateRecentThan);
     if ((lowerBound - m_articlesByDate.begin()) >= maxArticles)
         return false; // we reach max articles
@@ -376,7 +376,7 @@ void Feed::removeOldestArticle()
 
     m_articles.remove(oldestArticle->guid());
     m_articlesByDate.removeLast();
-    bool isRead = oldestArticle->isRead();
+    const bool isRead = oldestArticle->isRead();
     delete oldestArticle;
 
     if (!isRead)
@@ -402,8 +402,8 @@ void Feed::downloadIcon()
     // Download the RSS Feed icon
     // XXX: This works for most sites but it is not perfect
     const QUrl url(m_url);
-    auto iconUrl = QString("%1://%2/favicon.ico").arg(url.scheme(), url.host());
-    Net::DownloadHandler *handler = Net::DownloadManager::instance()->download(
+    const auto iconUrl = QString("%1://%2/favicon.ico").arg(url.scheme(), url.host());
+    const Net::DownloadHandler *handler = Net::DownloadManager::instance()->download(
             Net::DownloadRequest(iconUrl).saveToFile(true));
     connect(handler
             , static_cast<void (Net::DownloadHandler::*)(const QString &, const QString &)>(&Net::DownloadHandler::downloadFinished)
@@ -494,7 +494,7 @@ QString Feed::iconPath() const
     return m_iconPath;
 }
 
-QJsonValue Feed::toJsonValue(bool withData) const
+QJsonValue Feed::toJsonValue(const bool withData) const
 {
     QJsonObject jsonObj;
     jsonObj.insert(KEY_UID, uid().toString());
@@ -515,7 +515,7 @@ QJsonValue Feed::toJsonValue(bool withData) const
     return jsonObj;
 }
 
-void Feed::handleSessionProcessingEnabledChanged(bool enabled)
+void Feed::handleSessionProcessingEnabledChanged(const bool enabled)
 {
     if (enabled) {
         downloadIcon();
diff --git a/src/base/rss/rss_session.cpp b/src/base/rss/rss_session.cpp
index a2b546452..339329bc4 100644
--- a/src/base/rss/rss_session.cpp
+++ b/src/base/rss/rss_session.cpp
@@ -263,7 +263,7 @@ void Session::load()
     }
 
     QJsonParseError jsonError;
-    QJsonDocument jsonDoc = QJsonDocument::fromJson(itemsFile.readAll(), &jsonError);
+    const QJsonDocument jsonDoc = QJsonDocument::fromJson(itemsFile.readAll(), &jsonError);
     if (jsonError.error != QJsonParseError::NoError) {
         Logger::instance()->addMessage(
                     QString("Couldn't parse RSS Session data from %1. Error: %2")
@@ -482,7 +482,7 @@ uint Session::refreshInterval() const
     return m_refreshInterval;
 }
 
-void Session::setRefreshInterval(uint refreshInterval)
+void Session::setRefreshInterval(const uint refreshInterval)
 {
     if (m_refreshInterval != refreshInterval) {
         SettingsStorage::instance()->storeValue(SettingsKey_RefreshInterval, refreshInterval);
@@ -528,7 +528,7 @@ int Session::maxArticlesPerFeed() const
     return m_maxArticlesPerFeed;
 }
 
-void Session::setMaxArticlesPerFeed(int n)
+void Session::setMaxArticlesPerFeed(const int n)
 {
     if (m_maxArticlesPerFeed != n) {
         m_maxArticlesPerFeed = n;
diff --git a/src/base/scanfoldersmodel.cpp b/src/base/scanfoldersmodel.cpp
index 25a74b173..119b3eea9 100644
--- a/src/base/scanfoldersmodel.cpp
+++ b/src/base/scanfoldersmodel.cpp
@@ -183,7 +183,7 @@ bool ScanFoldersModel::setData(const QModelIndex &index, const QVariant &value,
         return false;
 
     if (role == Qt::UserRole) {
-        auto type = static_cast<PathType>(value.toInt());
+        const auto type = static_cast<PathType>(value.toInt());
         if (type == CUSTOM_LOCATION)
             return false;
 
@@ -192,7 +192,7 @@ bool ScanFoldersModel::setData(const QModelIndex &index, const QVariant &value,
         emit dataChanged(index, index);
     }
     else if (role == Qt::DisplayRole) {
-        QString path = value.toString();
+        const QString path = value.toString();
         if (path.isEmpty()) // means we didn't pass CUSTOM_LOCATION type
             return false;
 
@@ -209,14 +209,14 @@ bool ScanFoldersModel::setData(const QModelIndex &index, const QVariant &value,
 
 ScanFoldersModel::PathStatus ScanFoldersModel::addPath(const QString &watchPath, const PathType &downloadType, const QString &downloadPath, bool addToFSWatcher)
 {
-    QDir watchDir(watchPath);
+    const QDir watchDir(watchPath);
     if (!watchDir.exists()) return DoesNotExist;
     if (!watchDir.isReadable()) return CannotRead;
 
     const QString canonicalWatchPath = watchDir.canonicalPath();
     if (findPathData(canonicalWatchPath) != -1) return AlreadyInList;
 
-    QDir downloadDir(downloadPath);
+    const QDir downloadDir(downloadPath);
     const QString canonicalDownloadPath = downloadDir.canonicalPath();
 
     if (!m_fsWatcher) {
@@ -236,12 +236,12 @@ ScanFoldersModel::PathStatus ScanFoldersModel::addPath(const QString &watchPath,
 
 ScanFoldersModel::PathStatus ScanFoldersModel::updatePath(const QString &watchPath, const PathType &downloadType, const QString &downloadPath)
 {
-    QDir watchDir(watchPath);
+    const QDir watchDir(watchPath);
     const QString canonicalWatchPath = watchDir.canonicalPath();
-    int row = findPathData(canonicalWatchPath);
+    const int row = findPathData(canonicalWatchPath);
     if (row == -1) return DoesNotExist;
 
-    QDir downloadDir(downloadPath);
+    const QDir downloadDir(downloadPath);
     const QString canonicalDownloadPath = downloadDir.canonicalPath();
 
     m_pathList.at(row)->downloadType = downloadType;
@@ -256,13 +256,13 @@ void ScanFoldersModel::addToFSWatcher(const QStringList &watchPaths)
         return; // addPath() wasn't called before this
 
     for (const QString &path : watchPaths) {
-        QDir watchDir(path);
+        const QDir watchDir(path);
         const QString canonicalWatchPath = watchDir.canonicalPath();
         m_fsWatcher->addPath(canonicalWatchPath);
     }
 }
 
-void ScanFoldersModel::removePath(int row, bool removeFromFSWatcher)
+void ScanFoldersModel::removePath(const int row, const bool removeFromFSWatcher)
 {
     Q_ASSERT((row >= 0) && (row < rowCount()));
     beginRemoveRows(QModelIndex(), row, row);
@@ -272,7 +272,7 @@ void ScanFoldersModel::removePath(int row, bool removeFromFSWatcher)
     endRemoveRows();
 }
 
-bool ScanFoldersModel::removePath(const QString &path, bool removeFromFSWatcher)
+bool ScanFoldersModel::removePath(const QString &path, const bool removeFromFSWatcher)
 {
     const int row = findPathData(path);
     if (row == -1) return false;
@@ -291,7 +291,7 @@ bool ScanFoldersModel::downloadInWatchFolder(const QString &filePath) const
 {
     const int row = findPathData(QFileInfo(filePath).dir().path());
     Q_ASSERT(row != -1);
-    PathData *data = m_pathList.at(row);
+    const PathData *data = m_pathList.at(row);
     return (data->downloadType == DOWNLOAD_IN_WATCH_FOLDER);
 }
 
@@ -299,7 +299,7 @@ bool ScanFoldersModel::downloadInDefaultFolder(const QString &filePath) const
 {
     const int row = findPathData(QFileInfo(filePath).dir().path());
     Q_ASSERT(row != -1);
-    PathData *data = m_pathList.at(row);
+    const PathData *data = m_pathList.at(row);
     return (data->downloadType == DEFAULT_LOCATION);
 }
 
@@ -307,7 +307,7 @@ QString ScanFoldersModel::downloadPathTorrentFolder(const QString &filePath) con
 {
     const int row = findPathData(QFileInfo(filePath).dir().path());
     Q_ASSERT(row != -1);
-    PathData *data = m_pathList.at(row);
+    const PathData *data = m_pathList.at(row);
     if (data->downloadType == CUSTOM_LOCATION)
         return data->downloadPath;
 
@@ -375,7 +375,7 @@ void ScanFoldersModel::addTorrentsToSession(const QStringList &pathList)
             }
         }
         else {
-            BitTorrent::TorrentInfo torrentInfo = BitTorrent::TorrentInfo::loadFromFile(file);
+            const BitTorrent::TorrentInfo torrentInfo = BitTorrent::TorrentInfo::loadFromFile(file);
             if (torrentInfo.isValid()) {
                 BitTorrent::Session::instance()->addTorrent(torrentInfo, params);
                 Utils::Fs::forceRemove(file);
diff --git a/src/base/scanfoldersmodel.h b/src/base/scanfoldersmodel.h
index 9b77d9e37..a2c3e2151 100644
--- a/src/base/scanfoldersmodel.h
+++ b/src/base/scanfoldersmodel.h
@@ -68,10 +68,10 @@ public:
     static void freeInstance();
     static ScanFoldersModel *instance();
 
-    static QString pathTypeDisplayName(const PathType type);
+    static QString pathTypeDisplayName(PathType type);
 
-    int rowCount(const QModelIndex &parent = QModelIndex()) const;
-    int columnCount(const QModelIndex &parent = QModelIndex()) const;
+    int rowCount(const QModelIndex &parent = {}) const;
+    int columnCount(const QModelIndex &parent = {}) const;
     QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const;
     QVariant headerData(int section, Qt::Orientation orientation, int role = Qt::DisplayRole) const;
     Qt::ItemFlags flags(const QModelIndex &index) const;
diff --git a/src/base/search/searchhandler.cpp b/src/base/search/searchhandler.cpp
index 24d97e615..5cb820628 100644
--- a/src/base/search/searchhandler.cpp
+++ b/src/base/search/searchhandler.cpp
@@ -114,7 +114,7 @@ void SearchHandler::cancelSearch()
 // Slot called when QProcess is Finished
 // QProcess can be finished for 3 reasons:
 // Error | Stopped by user | Finished normally
-void SearchHandler::processFinished(int exitcode)
+void SearchHandler::processFinished(const int exitcode)
 {
     m_searchTimeout->stop();
 
diff --git a/src/base/search/searchpluginmanager.cpp b/src/base/search/searchpluginmanager.cpp
index 098979163..3bfd4d4de 100644
--- a/src/base/search/searchpluginmanager.cpp
+++ b/src/base/search/searchpluginmanager.cpp
@@ -168,9 +168,9 @@ PluginInfo *SearchPluginManager::pluginInfo(const QString &name) const
     return m_plugins.value(name);
 }
 
-void SearchPluginManager::enablePlugin(const QString &name, bool enabled)
+void SearchPluginManager::enablePlugin(const QString &name, const bool enabled)
 {
-    PluginInfo *plugin = m_plugins.value(name, 0);
+    PluginInfo *plugin = m_plugins.value(name, nullptr);
     if (plugin) {
         plugin->enabled = enabled;
         // Save to Hard disk
@@ -222,7 +222,7 @@ void SearchPluginManager::installPlugin(const QString &source)
 void SearchPluginManager::installPlugin_impl(const QString &name, const QString &path)
 {
     const PluginVersion newVersion = getPluginVersion(path);
-    PluginInfo *plugin = pluginInfo(name);
+    const PluginInfo *plugin = pluginInfo(name);
     if (plugin && !(plugin->version < newVersion)) {
         LogMsg(tr("Plugin already at version %1, which is greater than %2").arg(plugin->version, newVersion), Log::INFO);
         emit pluginUpdateFailed(name, tr("A more recent version of this plugin is already installed."));
@@ -230,7 +230,7 @@ void SearchPluginManager::installPlugin_impl(const QString &name, const QString
     }
 
     // Process with install
-    QString destPath = pluginPath(name);
+    const QString destPath = pluginPath(name);
     bool updated = false;
     if (QFile::exists(destPath)) {
         // Backup in case install fails
@@ -273,7 +273,7 @@ bool SearchPluginManager::uninstallPlugin(const QString &name)
     clearPythonCache(engineLocation());
 
     // remove it from hard drive
-    QDir pluginsFolder(pluginsLocation());
+    const QDir pluginsFolder(pluginsLocation());
     QStringList filters;
     filters << name + ".*";
     const QStringList files = pluginsFolder.entryList(filters, QDir::Files, QDir::Unsorted);
@@ -448,7 +448,7 @@ void SearchPluginManager::update()
     nova.start(Utils::ForeignApps::pythonInfo().executableName, params, QIODevice::ReadOnly);
     nova.waitForFinished();
 
-    QString capabilities = nova.readAll();
+    const QString capabilities = nova.readAll();
     QDomDocument xmlDoc;
     if (!xmlDoc.setContent(capabilities)) {
         qWarning() << "Could not parse Nova search engine capabilities, msg: " << capabilities.toLocal8Bit().data();
@@ -456,16 +456,16 @@ void SearchPluginManager::update()
         return;
     }
 
-    QDomElement root = xmlDoc.documentElement();
+    const QDomElement root = xmlDoc.documentElement();
     if (root.tagName() != "capabilities") {
         qWarning() << "Invalid XML file for Nova search engine capabilities, msg: " << capabilities.toLocal8Bit().data();
         return;
     }
 
     for (QDomNode engineNode = root.firstChild(); !engineNode.isNull(); engineNode = engineNode.nextSibling()) {
-        QDomElement engineElem = engineNode.toElement();
+        const QDomElement engineElem = engineNode.toElement();
         if (!engineElem.isNull()) {
-            QString pluginName = engineElem.tagName();
+            const QString pluginName = engineElem.tagName();
 
             std::unique_ptr<PluginInfo> plugin {new PluginInfo {}};
             plugin->name = pluginName;
@@ -480,7 +480,7 @@ void SearchPluginManager::update()
                     plugin->supportedCategories << cat;
             }
 
-            QStringList disabledEngines = Preferences::instance()->getSearchEngDisabled();
+            const QStringList disabledEngines = Preferences::instance()->getSearchEngDisabled();
             plugin->enabled = !disabledEngines.contains(pluginName);
 
             updateIconPath(plugin.get());
@@ -533,9 +533,9 @@ void SearchPluginManager::parseVersionInfo(const QByteArray &info)
     }
 }
 
-bool SearchPluginManager::isUpdateNeeded(const QString &pluginName, PluginVersion newVersion) const
+bool SearchPluginManager::isUpdateNeeded(const QString &pluginName, const PluginVersion newVersion) const
 {
-    PluginInfo *plugin = pluginInfo(pluginName);
+    const PluginInfo *plugin = pluginInfo(pluginName);
     if (!plugin) return true;
 
     PluginVersion oldVersion = plugin->version;
diff --git a/src/base/settingsstorage.h b/src/base/settingsstorage.h
index 15391f3eb..060e49a72 100644
--- a/src/base/settingsstorage.h
+++ b/src/base/settingsstorage.h
@@ -46,7 +46,7 @@ public:
     static void freeInstance();
     static SettingsStorage *instance();
 
-    QVariant loadValue(const QString &key, const QVariant &defaultValue = QVariant()) const;
+    QVariant loadValue(const QString &key, const QVariant &defaultValue = {}) const;
     void storeValue(const QString &key, const QVariant &value);
     void removeValue(const QString &key);
 
diff --git a/src/base/torrentfileguard.cpp b/src/base/torrentfileguard.cpp
index 55d34d499..736123b6d 100644
--- a/src/base/torrentfileguard.cpp
+++ b/src/base/torrentfileguard.cpp
@@ -37,7 +37,7 @@ FileGuard::FileGuard(const QString &path)
 {
 }
 
-void FileGuard::setAutoRemove(bool remove) noexcept
+void FileGuard::setAutoRemove(const bool remove) noexcept
 {
     m_remove = remove;
 }
@@ -48,7 +48,7 @@ FileGuard::~FileGuard()
         Utils::Fs::forceRemove(m_path); // forceRemove() checks for file existence
 }
 
-TorrentFileGuard::TorrentFileGuard(const QString &path, TorrentFileGuard::AutoDeleteMode mode)
+TorrentFileGuard::TorrentFileGuard(const QString &path, const TorrentFileGuard::AutoDeleteMode mode)
     : FileGuard {mode != Never ? path : QString()}
     , m_mode {mode}
     , m_wasAdded {false}
diff --git a/src/base/torrentfileguard.h b/src/base/torrentfileguard.h
index 0ca772c94..f378a01c0 100644
--- a/src/base/torrentfileguard.h
+++ b/src/base/torrentfileguard.h
@@ -37,7 +37,7 @@ template <typename T> class CachedSettingValue;
 class FileGuard
 {
 public:
-    explicit FileGuard(const QString &path = QString());
+    explicit FileGuard(const QString &path = {});
     ~FileGuard();
 
     /// Cancels or re-enables deferred file deletion
@@ -55,7 +55,7 @@ class TorrentFileGuard : private FileGuard
     Q_GADGET
 
 public:
-    explicit TorrentFileGuard(const QString &path = QString());
+    explicit TorrentFileGuard(const QString &path = {});
     ~TorrentFileGuard();
 
     /// marks the torrent file as loaded (added) into the BitTorrent::Session
diff --git a/src/base/torrentfilter.h b/src/base/torrentfilter.h
index c4012f75d..350e3f7a7 100644
--- a/src/base/torrentfilter.h
+++ b/src/base/torrentfilter.h
@@ -72,7 +72,7 @@ public:
     TorrentFilter();
     // category & tags: pass empty string for uncategorized / untagged torrents.
     // Pass null string (QString()) to disable filtering (i.e. all torrents).
-    TorrentFilter(const Type type, const QStringSet &hashSet = AnyHash, const QString &category = AnyCategory, const QString &tag = AnyTag);
+    TorrentFilter(Type type, const QStringSet &hashSet = AnyHash, const QString &category = AnyCategory, const QString &tag = AnyTag);
     TorrentFilter(const QString &filter, const QStringSet &hashSet = AnyHash, const QString &category = AnyCategory, const QString &tags = AnyTag);
 
     bool setType(Type type);
diff --git a/src/base/utils/bytearray.h b/src/base/utils/bytearray.h
index e0f46abf3..a9e6e89ea 100644
--- a/src/base/utils/bytearray.h
+++ b/src/base/utils/bytearray.h
@@ -40,6 +40,6 @@ namespace Utils
 
         // Mimic QByteArray::mid(pos, len) but instead of returning a full-copy,
         // we only return a partial view
-        const QByteArray midView(const QByteArray &in, const int pos, const int len = -1);
+        const QByteArray midView(const QByteArray &in, int pos, int len = -1);
     }
 }
diff --git a/src/base/utils/foreignapps.cpp b/src/base/utils/foreignapps.cpp
index 5a2de1b39..8047a827d 100644
--- a/src/base/utils/foreignapps.cpp
+++ b/src/base/utils/foreignapps.cpp
@@ -119,7 +119,7 @@ namespace
         return keys;
     }
 
-    QString getRegValue(const HKEY handle, const QString &name = QString())
+    QString getRegValue(const HKEY handle, const QString &name = {})
     {
         QString result;
 
diff --git a/src/base/utils/fs.cpp b/src/base/utils/fs.cpp
index eabe5a91d..ae9d1d31a 100644
--- a/src/base/utils/fs.cpp
+++ b/src/base/utils/fs.cpp
@@ -81,14 +81,14 @@ QString Utils::Fs::fromNativePath(const QString &path)
  */
 QString Utils::Fs::fileExtension(const QString &filename)
 {
-    QString ext = QString(filename).remove(QB_EXT);
+    const QString ext = QString(filename).remove(QB_EXT);
     const int pointIndex = ext.lastIndexOf('.');
     return (pointIndex >= 0) ? ext.mid(pointIndex + 1) : QString();
 }
 
 QString Utils::Fs::fileName(const QString &filePath)
 {
-    QString path = fromNativePath(filePath);
+    const QString path = fromNativePath(filePath);
     const int slashIndex = path.lastIndexOf('/');
     if (slashIndex == -1)
         return path;
@@ -97,7 +97,7 @@ QString Utils::Fs::fileName(const QString &filePath)
 
 QString Utils::Fs::folderName(const QString &filePath)
 {
-    QString path = fromNativePath(filePath);
+    const QString path = fromNativePath(filePath);
     const int slashIndex = path.lastIndexOf('/');
     if (slashIndex == -1)
         return path;
@@ -140,7 +140,7 @@ bool Utils::Fs::smartRemoveEmptyFolderTree(const QString &path)
         }
 
         // remove temp files on linux (file ends with '~'), e.g. `filename~`
-        QDir dir(p);
+        const QDir dir(p);
         const QStringList tmpFileList = dir.entryList(QDir::Files);
         for (const QString &f : tmpFileList) {
             if (f.endsWith('~'))
@@ -188,7 +188,7 @@ void Utils::Fs::removeDirRecursive(const QString &path)
 qint64 Utils::Fs::computePathSize(const QString &path)
 {
     // Check if it is a file
-    QFileInfo fi(path);
+    const QFileInfo fi(path);
     if (!fi.exists()) return -1;
     if (fi.isFile()) return fi.size();
 
@@ -221,7 +221,7 @@ bool Utils::Fs::sameFiles(const QString &path1, const QString &path2)
     return true;
 }
 
-QString Utils::Fs::toValidFileSystemName(const QString &name, bool allowSeparators, const QString &pad)
+QString Utils::Fs::toValidFileSystemName(const QString &name, const bool allowSeparators, const QString &pad)
 {
     const QRegularExpression regex(allowSeparators ? "[:?\"*<>|]+" : "[\\\\/:?\"*<>|]+");
 
@@ -232,7 +232,7 @@ QString Utils::Fs::toValidFileSystemName(const QString &name, bool allowSeparato
     return validName;
 }
 
-bool Utils::Fs::isValidFileSystemName(const QString &name, bool allowSeparators)
+bool Utils::Fs::isValidFileSystemName(const QString &name, const bool allowSeparators)
 {
     if (name.isEmpty()) return false;
 
@@ -272,7 +272,7 @@ bool Utils::Fs::sameFileNames(const QString &first, const QString &second)
 
 QString Utils::Fs::expandPath(const QString &path)
 {
-    QString ret = path.trimmed();
+    const QString ret = path.trimmed();
     if (ret.isEmpty())
         return ret;
 
diff --git a/src/base/utils/misc.cpp b/src/base/utils/misc.cpp
index d9aa0d180..259151fec 100644
--- a/src/base/utils/misc.cpp
+++ b/src/base/utils/misc.cpp
@@ -252,10 +252,10 @@ QPoint Utils::Misc::screenCenter(const QWidget *w)
 {
     // Returns the QPoint which the widget will be placed center on screen (where parent resides)
 
-    QWidget *parent = w->parentWidget();
-    QDesktopWidget *desktop = QApplication::desktop();
-    int scrn = desktop->screenNumber(parent);  // fallback to `primaryScreen` when parent is invalid
-    QRect r = desktop->availableGeometry(scrn);
+    const QWidget *parent = w->parentWidget();
+    const QDesktopWidget *desktop = QApplication::desktop();
+    const int scrn = desktop->screenNumber(parent);  // fallback to `primaryScreen` when parent is invalid
+    const QRect r = desktop->availableGeometry(scrn);
     return {r.x() + (r.width() - w->frameSize().width()) / 2, r.y() + (r.height() - w->frameSize().height()) / 2};
 }
 #endif
@@ -269,7 +269,7 @@ QString Utils::Misc::unitString(const SizeUnit unit, const bool isSpeed)
     return ret;
 }
 
-QString Utils::Misc::friendlyUnit(qint64 bytesValue, bool isSpeed)
+QString Utils::Misc::friendlyUnit(const qint64 bytesValue, const bool isSpeed)
 {
     SizeUnit unit;
     qreal friendlyVal;
@@ -289,7 +289,7 @@ int Utils::Misc::friendlyUnitPrecision(SizeUnit unit)
     return 3;
 }
 
-qlonglong Utils::Misc::sizeInBytes(qreal size, Utils::Misc::SizeUnit unit)
+qlonglong Utils::Misc::sizeInBytes(qreal size, const Utils::Misc::SizeUnit unit)
 {
     for (int i = 0; i < static_cast<int>(unit); ++i)
         size *= 1024;
@@ -347,7 +347,7 @@ bool Utils::Misc::isPreviewable(const QString &extension)
 
 // Take a number of seconds and return an user-friendly
 // time duration like "1d 2h 10m".
-QString Utils::Misc::userFriendlyDuration(qlonglong seconds)
+QString Utils::Misc::userFriendlyDuration(const qlonglong seconds)
 {
     if ((seconds < 0) || (seconds >= MAX_ETA))
         return QString::fromUtf8(C_INFINITY);
@@ -511,7 +511,7 @@ void Utils::Misc::openFolderSelect(const QString &absolutePath)
     QProcess proc;
     proc.start("xdg-mime", {"query", "default", "inode/directory"});
     proc.waitForFinished();
-    QString output = proc.readLine().simplified();
+    const QString output = proc.readLine().simplified();
     if ((output == "dolphin.desktop") || (output == "org.kde.dolphin.desktop")) {
         proc.startDetached("dolphin", {"--select", Utils::Fs::toNativePath(path)});
     }
diff --git a/src/base/utils/random.h b/src/base/utils/random.h
index 6e3a30c0e..93448191a 100644
--- a/src/base/utils/random.h
+++ b/src/base/utils/random.h
@@ -35,7 +35,7 @@ namespace Utils
 {
     namespace Random
     {
-        uint32_t rand(const uint32_t min = 0, const uint32_t max = UINT32_MAX);
+        uint32_t rand(uint32_t min = 0, uint32_t max = UINT32_MAX);
     }
 }
 
diff --git a/src/base/utils/string.cpp b/src/base/utils/string.cpp
index 6ed656c3e..f8c0d6396 100644
--- a/src/base/utils/string.cpp
+++ b/src/base/utils/string.cpp
@@ -151,7 +151,7 @@ int Utils::String::naturalCompare(const QString &left, const QString &right, con
 }
 
 // to send numbers instead of strings with suffixes
-QString Utils::String::fromDouble(double n, int precision)
+QString Utils::String::fromDouble(const double n, const int precision)
 {
     /* HACK because QString rounds up. Eg QString::number(0.999*100.0, 'f' ,1) == 99.9
     ** but QString::number(0.9999*100.0, 'f' ,1) == 100.0 The problem manifests when
@@ -159,7 +159,7 @@ QString Utils::String::fromDouble(double n, int precision)
     ** our 'wanted' is >= 5. In this case our last digit gets rounded up. So for each
     ** precision we add an extra 0 behind 1 in the below algorithm. */
 
-    double prec = std::pow(10.0, precision);
+    const double prec = std::pow(10.0, precision);
     return QLocale::system().toString(std::floor(n * prec) / prec, 'f', precision);
 }
 
diff --git a/src/base/utils/string.h b/src/base/utils/string.h
index d90640919..c5cf43c78 100644
--- a/src/base/utils/string.h
+++ b/src/base/utils/string.h
@@ -63,7 +63,7 @@ namespace Utils
             return str;
         }
 
-        bool parseBool(const QString &string, const bool defaultValue);
+        bool parseBool(const QString &string, bool defaultValue);
         TriStateBool parseTriStateBool(const QString &string);
     }
 }
diff --git a/src/gui/addnewtorrentdialog.cpp b/src/gui/addnewtorrentdialog.cpp
index ee389dbdd..0a6d15f8d 100644
--- a/src/gui/addnewtorrentdialog.cpp
+++ b/src/gui/addnewtorrentdialog.cpp
@@ -106,7 +106,7 @@ AddNewTorrentDialog::AddNewTorrentDialog(const BitTorrent::AddTorrentParams &inP
     setModal(true);
 #endif
 
-    auto session = BitTorrent::Session::instance();
+    const auto *session = BitTorrent::Session::instance();
 
     if (m_torrentParams.addPaused == TriStateBool::True)
         m_ui->startTorrentCheckBox->setChecked(false);
@@ -233,7 +233,7 @@ void AddNewTorrentDialog::saveState()
 
 void AddNewTorrentDialog::show(const QString &source, const BitTorrent::AddTorrentParams &inParams, QWidget *parent)
 {
-    AddNewTorrentDialog *dlg = new AddNewTorrentDialog(inParams, parent);
+    auto *dlg = new AddNewTorrentDialog(inParams, parent);
 
     if (Net::DownloadManager::hasSupportedScheme(source)) {
         // Launch downloader
diff --git a/src/gui/addnewtorrentdialog.h b/src/gui/addnewtorrentdialog.h
index f6c4b8e06..a3e3f2197 100644
--- a/src/gui/addnewtorrentdialog.h
+++ b/src/gui/addnewtorrentdialog.h
@@ -98,7 +98,7 @@ private:
     int indexOfSavePath(const QString &savePath);
     void loadState();
     void saveState();
-    void setMetadataProgressIndicator(bool visibleIndicator, const QString &labelText = QString());
+    void setMetadataProgressIndicator(bool visibleIndicator, const QString &labelText = {});
     void setupTreeview();
     void setCommentText(const QString &str) const;
     void setSavePath(const QString &newPath);
diff --git a/src/gui/autoexpandabledialog.h b/src/gui/autoexpandabledialog.h
index 2768304be..73f2cdbad 100644
--- a/src/gui/autoexpandabledialog.h
+++ b/src/gui/autoexpandabledialog.h
@@ -47,7 +47,7 @@ public:
     ~AutoExpandableDialog();
 
     static QString getText(QWidget *parent, const QString &title, const QString &label,
-                            QLineEdit::EchoMode mode = QLineEdit::Normal, const QString &text = QString(),
+                           QLineEdit::EchoMode mode = QLineEdit::Normal, const QString &text = {},
                             bool *ok = nullptr, bool excludeExtension = false, Qt::InputMethodHints inputMethodHints = Qt::ImhNone);
 
 protected:
diff --git a/src/gui/categoryfiltermodel.cpp b/src/gui/categoryfiltermodel.cpp
index 0e0dcd84e..71ce34df5 100644
--- a/src/gui/categoryfiltermodel.cpp
+++ b/src/gui/categoryfiltermodel.cpp
@@ -176,7 +176,7 @@ CategoryFilterModel::CategoryFilterModel(QObject *parent)
     , m_rootItem(new CategoryModelItem)
 {
     using namespace BitTorrent;
-    auto session = Session::instance();
+    const auto *session = Session::instance();
 
     connect(session, &Session::categoryAdded, this, &CategoryFilterModel::categoryAdded);
     connect(session, &Session::categoryRemoved, this, &CategoryFilterModel::categoryRemoved);
@@ -209,7 +209,7 @@ QVariant CategoryFilterModel::data(const QModelIndex &index, int role) const
 {
     if (!index.isValid()) return {};
 
-    auto item = static_cast<CategoryModelItem *>(index.internalPointer());
+    auto item = static_cast<const CategoryModelItem *>(index.internalPointer());
 
     if ((index.column() == 0) && (role == Qt::DecorationRole)) {
         return GuiIconProvider::instance()->getIcon("inode-directory");
@@ -384,8 +384,8 @@ void CategoryFilterModel::populate()
 {
     m_rootItem->clear();
 
-    auto session = BitTorrent::Session::instance();
-    auto torrents = session->torrents();
+    const auto *session = BitTorrent::Session::instance();
+    const auto torrents = session->torrents();
     m_isSubcategoriesEnabled = session->isSubcategoriesEnabled();
 
     const QString UID_ALL;
@@ -413,7 +413,7 @@ void CategoryFilterModel::populate()
                 if (!parent->hasChild(subcatName)) {
                     new CategoryModelItem(
                                 parent, subcatName
-                                , std::count_if(torrents.begin(), torrents.end()
+                                , std::count_if(torrents.cbegin(), torrents.cend()
                                                 , [subcat](Torrent *torrent) { return torrent->category() == subcat; }));
                 }
                 parent = parent->child(subcatName);
diff --git a/src/gui/categoryfiltermodel.h b/src/gui/categoryfiltermodel.h
index 15609ccbf..2fd058fb0 100644
--- a/src/gui/categoryfiltermodel.h
+++ b/src/gui/categoryfiltermodel.h
@@ -49,13 +49,13 @@ public:
 
     static bool isSpecialItem(const QModelIndex &index);
 
-    int columnCount(const QModelIndex &parent = QModelIndex()) const override;
+    int columnCount(const QModelIndex &parent = {}) const override;
     QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override;
     Qt::ItemFlags flags(const QModelIndex &index) const override;
     QVariant headerData(int section, Qt::Orientation orientation, int role) const override;
-    QModelIndex index(int row, int column, const QModelIndex &parent = QModelIndex()) const override;
+    QModelIndex index(int row, int column, const QModelIndex &parent = {}) const override;
     QModelIndex parent(const QModelIndex &index) const override;
-    int rowCount(const QModelIndex &parent = QModelIndex()) const override;
+    int rowCount(const QModelIndex &parent = {}) const override;
 
     QModelIndex index(const QString &categoryName) const;
     QString categoryName(const QModelIndex &index) const;
diff --git a/src/gui/categoryfilterwidget.cpp b/src/gui/categoryfilterwidget.cpp
index 9c5f3a09b..9bc7032c8 100644
--- a/src/gui/categoryfilterwidget.cpp
+++ b/src/gui/categoryfilterwidget.cpp
@@ -91,7 +91,7 @@ CategoryFilterWidget::CategoryFilterWidget(QWidget *parent)
 QString CategoryFilterWidget::currentCategory() const
 {
     QModelIndex current;
-    auto selectedRows = selectionModel()->selectedRows();
+    const auto selectedRows = selectionModel()->selectedRows();
     if (!selectedRows.isEmpty())
         current = selectedRows.first();
 
@@ -114,7 +114,7 @@ void CategoryFilterWidget::showMenu(QPoint)
                           , tr("Add category..."));
     connect(addAct, &QAction::triggered, this, &CategoryFilterWidget::addCategory);
 
-    auto selectedRows = selectionModel()->selectedRows();
+    const auto selectedRows = selectionModel()->selectedRows();
     if (!selectedRows.empty() && !CategoryFilterModel::isSpecialItem(selectedRows.first())) {
         if (BitTorrent::Session::instance()->isSubcategoriesEnabled()) {
             QAction *addSubAct = menu.addAction(
@@ -220,7 +220,7 @@ void CategoryFilterWidget::editCategory()
 
 void CategoryFilterWidget::removeCategory()
 {
-    auto selectedRows = selectionModel()->selectedRows();
+    const auto selectedRows = selectionModel()->selectedRows();
     if (!selectedRows.empty() && !CategoryFilterModel::isSpecialItem(selectedRows.first())) {
         BitTorrent::Session::instance()->removeCategory(
                     static_cast<CategoryFilterProxyModel *>(model())->categoryName(selectedRows.first()));
diff --git a/src/gui/cookiesmodel.h b/src/gui/cookiesmodel.h
index 4e203123d..7d12472be 100644
--- a/src/gui/cookiesmodel.h
+++ b/src/gui/cookiesmodel.h
@@ -54,18 +54,18 @@ public:
     QList<QNetworkCookie> cookies() const;
 
     QVariant headerData(int section, Qt::Orientation orientation, int role = Qt::DisplayRole) const override;
-    QModelIndex index(int row, int column, const QModelIndex &parent = QModelIndex()) const override;
+    QModelIndex index(int row, int column, const QModelIndex &parent = {}) const override;
     QModelIndex parent(const QModelIndex &index) const override;
 
-    int rowCount(const QModelIndex &parent = QModelIndex()) const override;
-    int columnCount(const QModelIndex &parent = QModelIndex()) const override;
+    int rowCount(const QModelIndex &parent = {}) const override;
+    int columnCount(const QModelIndex &parent = {}) const override;
 
     Qt::ItemFlags flags(const QModelIndex &index) const override;
     QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override;
 
     bool setData(const QModelIndex &index, const QVariant &value, int role) override;
-    bool insertRows(int row, int count, const QModelIndex &parent = QModelIndex()) override;
-    bool removeRows(int row, int count, const QModelIndex &parent = QModelIndex()) override;
+    bool insertRows(int row, int count, const QModelIndex &parent = {}) override;
+    bool removeRows(int row, int count, const QModelIndex &parent = {}) override;
 
 private:
     mutable QList<QNetworkCookie> m_cookies;
diff --git a/src/gui/mainwindow.h b/src/gui/mainwindow.h
index 52168ad5e..f02983921 100644
--- a/src/gui/mainwindow.h
+++ b/src/gui/mainwindow.h
@@ -84,7 +84,7 @@ public:
     bool isExecutionLogEnabled() const;
     void setExecutionLogEnabled(bool value);
     int executionLogMsgTypes() const;
-    void setExecutionLogMsgTypes(const int value);
+    void setExecutionLogMsgTypes(int value);
 
     // Notifications properties
     bool isNotificationsEnabled() const;
@@ -209,7 +209,7 @@ private:
     bool event(QEvent *e) override;
     void displayRSSTab(bool enable);
     void displaySearchTab(bool enable);
-    void createTorrentTriggered(const QString &path = QString());
+    void createTorrentTriggered(const QString &path = {});
     void showStatusBar(bool show);
 
     Ui::MainWindow *m_ui;
diff --git a/src/gui/optionsdialog.cpp b/src/gui/optionsdialog.cpp
index c9ba13e01..14a7d34b7 100644
--- a/src/gui/optionsdialog.cpp
+++ b/src/gui/optionsdialog.cpp
@@ -846,7 +846,7 @@ void OptionsDialog::loadOptions()
     m_ui->spinRSSRefreshInterval->setValue(RSS::Session::instance()->refreshInterval());
     m_ui->spinRSSMaxArticlesPerFeed->setValue(RSS::Session::instance()->maxArticlesPerFeed());
 
-    auto session = BitTorrent::Session::instance();
+    const auto *session = BitTorrent::Session::instance();
 
     // Downloads preferences
     m_ui->checkAdditionDialog->setChecked(AddNewTorrentDialog::isEnabled());
@@ -974,7 +974,7 @@ void OptionsDialog::loadOptions()
         m_ui->spinMaxUploadsPerTorrent->setEnabled(false);
     }
 
-    auto proxyConfigManager = Net::ProxyConfigurationManager::instance();
+    const auto *proxyConfigManager = Net::ProxyConfigurationManager::instance();
     Net::ProxyConfiguration proxyConf = proxyConfigManager->proxyConfiguration();
     using Net::ProxyType;
     bool useProxyAuth = false;
diff --git a/src/gui/properties/piecesbar.cpp b/src/gui/properties/piecesbar.cpp
index 2836923ca..276261111 100644
--- a/src/gui/properties/piecesbar.cpp
+++ b/src/gui/properties/piecesbar.cpp
@@ -118,7 +118,7 @@ PiecesBar::PiecesBar(QWidget *parent)
     setMouseTracking(true);
 }
 
-void PiecesBar::setTorrent(BitTorrent::TorrentHandle *torrent)
+void PiecesBar::setTorrent(const BitTorrent::TorrentHandle *torrent)
 {
     m_torrent = torrent;
     if (!m_torrent)
diff --git a/src/gui/properties/piecesbar.h b/src/gui/properties/piecesbar.h
index ac0575a16..0e7a335fc 100644
--- a/src/gui/properties/piecesbar.h
+++ b/src/gui/properties/piecesbar.h
@@ -50,7 +50,7 @@ class PiecesBar : public QWidget
 public:
     explicit PiecesBar(QWidget *parent = nullptr);
 
-    void setTorrent(BitTorrent::TorrentHandle *torrent);
+    void setTorrent(const BitTorrent::TorrentHandle *torrent);
     void setColors(const QColor &background, const QColor &border, const QColor &complete);
 
     virtual void clear();
diff --git a/src/gui/rss/automatedrssdownloader.cpp b/src/gui/rss/automatedrssdownloader.cpp
index dccc5fd07..b5179a33f 100644
--- a/src/gui/rss/automatedrssdownloader.cpp
+++ b/src/gui/rss/automatedrssdownloader.cpp
@@ -213,7 +213,7 @@ void AutomatedRssDownloader::updateFeedList()
         bool anyEnabled = false;
 
         for (const QListWidgetItem *ruleItem : asConst(selection)) {
-            auto rule = RSS::AutoDownloader::instance()->ruleByName(ruleItem->text());
+            const auto rule = RSS::AutoDownloader::instance()->ruleByName(ruleItem->text());
             if (rule.feedURLs().contains(feedURL))
                 anyEnabled = true;
             else
diff --git a/src/gui/search/searchsortmodel.h b/src/gui/search/searchsortmodel.h
index 369058de7..6434b3dcd 100644
--- a/src/gui/search/searchsortmodel.h
+++ b/src/gui/search/searchsortmodel.h
@@ -53,7 +53,7 @@ public:
     explicit SearchSortModel(QObject *parent = nullptr);
 
     void enableNameFilter(bool enabled);
-    void setNameFilter(const QString &searchTerm = QString());
+    void setNameFilter(const QString &searchTerm = {});
 
     //! \brief Sets parameters for filtering by size
     //! \param minSize minimal size in bytes
diff --git a/src/gui/search/searchwidget.cpp b/src/gui/search/searchwidget.cpp
index 0b9794ea0..748a501fe 100644
--- a/src/gui/search/searchwidget.cpp
+++ b/src/gui/search/searchwidget.cpp
@@ -134,7 +134,7 @@ SearchWidget::SearchWidget(MainWindow *mainWindow)
     connect(m_tabStatusChangedMapper, static_cast<void (QSignalMapper::*)(QWidget *)>(&QSignalMapper::mapped)
             , this, &SearchWidget::tabStatusChanged);
 
-    auto *searchManager = SearchPluginManager::instance();
+    const auto *searchManager = SearchPluginManager::instance();
     const auto onPluginChanged = [this]()
     {
         fillPluginComboBox();
diff --git a/src/gui/tagfiltermodel.cpp b/src/gui/tagfiltermodel.cpp
index 82dbd8365..d2a98615a 100644
--- a/src/gui/tagfiltermodel.cpp
+++ b/src/gui/tagfiltermodel.cpp
@@ -92,7 +92,7 @@ TagFilterModel::TagFilterModel(QObject *parent)
     : QAbstractListModel(parent)
 {
     using Session = BitTorrent::Session;
-    auto session = Session::instance();
+    const auto *session = Session::instance();
 
     connect(session, &Session::tagAdded, this, &TagFilterModel::tagAdded);
     connect(session, &Session::tagRemoved, this, &TagFilterModel::tagRemoved);
@@ -265,18 +265,18 @@ void TagFilterModel::populate()
 {
     using Torrent = BitTorrent::TorrentHandle;
 
-    auto session = BitTorrent::Session::instance();
-    auto torrents = session->torrents();
+    const auto *session = BitTorrent::Session::instance();
+    const auto torrents = session->torrents();
 
     // All torrents
     addToModel(getSpecialAllTag(), torrents.count());
 
-    const int untaggedCount = std::count_if(torrents.begin(), torrents.end(),
+    const int untaggedCount = std::count_if(torrents.cbegin(), torrents.cend(),
                                              [](Torrent *torrent) { return torrent->tags().isEmpty(); });
     addToModel(getSpecialUntaggedTag(), untaggedCount);
 
     for (const QString &tag : asConst(session->tags())) {
-        const int count = std::count_if(torrents.begin(), torrents.end(),
+        const int count = std::count_if(torrents.cbegin(), torrents.cend(),
                                         [tag](Torrent *torrent) { return torrent->hasTag(tag); });
         addToModel(tag, count);
     }
diff --git a/src/gui/tagfiltermodel.h b/src/gui/tagfiltermodel.h
index c1efaf76f..19451bf94 100644
--- a/src/gui/tagfiltermodel.h
+++ b/src/gui/tagfiltermodel.h
@@ -54,8 +54,8 @@ public:
     QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override;
     Qt::ItemFlags flags(const QModelIndex &index) const override;
     QVariant headerData(int section, Qt::Orientation orientation, int role) const override;
-    QModelIndex index(int row, int column, const QModelIndex &parent = QModelIndex()) const override;
-    int rowCount(const QModelIndex &parent = QModelIndex()) const override;
+    QModelIndex index(int row, int column, const QModelIndex &parent = {}) const override;
+    int rowCount(const QModelIndex &parent = {}) const override;
 
     QModelIndex index(const QString &tag) const;
     QString tag(const QModelIndex &index) const;
diff --git a/src/gui/tagfilterwidget.cpp b/src/gui/tagfilterwidget.cpp
index c5c5f1fbb..453e4ea07 100644
--- a/src/gui/tagfilterwidget.cpp
+++ b/src/gui/tagfilterwidget.cpp
@@ -90,7 +90,7 @@ TagFilterWidget::TagFilterWidget(QWidget *parent)
 QString TagFilterWidget::currentTag() const
 {
     QModelIndex current;
-    auto selectedRows = selectionModel()->selectedRows();
+    const auto selectedRows = selectionModel()->selectedRows();
     if (!selectedRows.isEmpty())
         current = selectedRows.first();
 
@@ -113,7 +113,7 @@ void TagFilterWidget::showMenu(QPoint)
         , tr("Add tag..."));
     connect(addAct, &QAction::triggered, this, &TagFilterWidget::addTag);
 
-    auto selectedRows = selectionModel()->selectedRows();
+    const auto selectedRows = selectionModel()->selectedRows();
     if (!selectedRows.empty() && !TagFilterModel::isSpecialItem(selectedRows.first())) {
         QAction *removeAct = menu.addAction(
             GuiIconProvider::instance()->getIcon("list-remove")
@@ -212,7 +212,7 @@ void TagFilterWidget::addTag()
 
 void TagFilterWidget::removeTag()
 {
-    auto selectedRows = selectionModel()->selectedRows();
+    const auto selectedRows = selectionModel()->selectedRows();
     if (!selectedRows.empty() && !TagFilterModel::isSpecialItem(selectedRows.first())) {
         BitTorrent::Session::instance()->removeTag(
             static_cast<TagFilterProxyModel *>(model())->tag(selectedRows.first()));
diff --git a/src/gui/torrentcategorydialog.h b/src/gui/torrentcategorydialog.h
index 9addebb8f..54d6f0eeb 100644
--- a/src/gui/torrentcategorydialog.h
+++ b/src/gui/torrentcategorydialog.h
@@ -41,7 +41,7 @@ class TorrentCategoryDialog : public QDialog
     Q_DISABLE_COPY(TorrentCategoryDialog)
 
 public:
-    static QString createCategory(QWidget *parent, const QString &parentCategoryName = QString());
+    static QString createCategory(QWidget *parent, const QString &parentCategoryName = {});
     static void editCategory(QWidget *parent, const QString &categoryName);
 
     explicit TorrentCategoryDialog(QWidget *parent = nullptr);
diff --git a/src/gui/torrentcontentmodel.h b/src/gui/torrentcontentmodel.h
index 921310ef9..1f6980af2 100644
--- a/src/gui/torrentcontentmodel.h
+++ b/src/gui/torrentcontentmodel.h
@@ -53,16 +53,16 @@ public:
     void updateFilesAvailability(const QVector<qreal> &fa);
     QVector<int> getFilePriorities() const;
     bool allFiltered() const;
-    int columnCount(const QModelIndex &parent = QModelIndex()) const override;
+    int columnCount(const QModelIndex &parent = {}) const override;
     bool setData(const QModelIndex &index, const QVariant &value, int role = Qt::EditRole) override;
     TorrentContentModelItem::ItemType itemType(const QModelIndex &index) const;
     int getFileIndex(const QModelIndex &index);
     QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override;
     Qt::ItemFlags flags(const QModelIndex &index) const override;
     QVariant headerData(int section, Qt::Orientation orientation, int role) const override;
-    QModelIndex index(int row, int column, const QModelIndex &parent = QModelIndex()) const override;
+    QModelIndex index(int row, int column, const QModelIndex &parent = {}) const override;
     QModelIndex parent(const QModelIndex &index) const override;
-    int rowCount(const QModelIndex &parent = QModelIndex()) const override;
+    int rowCount(const QModelIndex &parent = {}) const override;
     void clear();
     void setupModelData(const BitTorrent::TorrentInfo &info);
 
diff --git a/src/gui/torrentcreatordialog.h b/src/gui/torrentcreatordialog.h
index 1362c0f62..bd94475bf 100644
--- a/src/gui/torrentcreatordialog.h
+++ b/src/gui/torrentcreatordialog.h
@@ -49,7 +49,7 @@ class TorrentCreatorDialog : public QDialog
     Q_OBJECT
 
 public:
-    TorrentCreatorDialog(QWidget *parent = nullptr, const QString &defaultPath = QString());
+    TorrentCreatorDialog(QWidget *parent = nullptr, const QString &defaultPath = {});
     ~TorrentCreatorDialog() override;
     void updateInputPath(const QString &path);
 
diff --git a/src/gui/transferlistmodel.cpp b/src/gui/transferlistmodel.cpp
index d182d615a..9d69d5da4 100644
--- a/src/gui/transferlistmodel.cpp
+++ b/src/gui/transferlistmodel.cpp
@@ -149,7 +149,7 @@ QVariant TransferListModel::headerData(int section, Qt::Orientation orientation,
             case TR_RATIO:
             case TR_PRIORITY:
             case TR_LAST_ACTIVITY:
-                return {Qt::AlignRight | Qt::AlignVCenter};
+                return QVariant(Qt::AlignRight | Qt::AlignVCenter);
             default:
                 return QAbstractListModel::headerData(section, orientation, role);
             }
diff --git a/src/gui/transferlistmodel.h b/src/gui/transferlistmodel.h
index a7eb4bf24..92ea137e7 100644
--- a/src/gui/transferlistmodel.h
+++ b/src/gui/transferlistmodel.h
@@ -83,7 +83,7 @@ public:
 
     explicit TransferListModel(QObject *parent = nullptr);
 
-    int rowCount(const QModelIndex &index = QModelIndex()) const override;
+    int rowCount(const QModelIndex &index = {}) const override;
     int columnCount(const QModelIndex &parent=QModelIndex()) const override;
     QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override;
     bool setData(const QModelIndex &index, const QVariant &value, int role) override;
diff --git a/src/gui/transferlistsortmodel.h b/src/gui/transferlistsortmodel.h
index e8581b136..b5355f9e9 100644
--- a/src/gui/transferlistsortmodel.h
+++ b/src/gui/transferlistsortmodel.h
@@ -52,7 +52,7 @@ public:
 private:
     bool lessThan(const QModelIndex &left, const QModelIndex &right) const override;
     bool lowerPositionThan(const QModelIndex &left, const QModelIndex &right) const;
-    bool dateLessThan(const int dateColumn, const QModelIndex &left, const QModelIndex &right, bool sortInvalidInBottom) const;
+    bool dateLessThan(int dateColumn, const QModelIndex &left, const QModelIndex &right, bool sortInvalidInBottom) const;
     bool filterAcceptsRow(int sourceRow, const QModelIndex &sourceParent) const override;
     bool matchFilter(int sourceRow, const QModelIndex &sourceParent) const;
 
diff --git a/src/gui/utils.h b/src/gui/utils.h
index 35502abe3..ee1c7e76d 100644
--- a/src/gui/utils.h
+++ b/src/gui/utils.h
@@ -49,9 +49,9 @@ namespace Utils
             return (size * screenScalingFactor(widget));
         }
 
-        QPixmap scaledPixmap(const QIcon &icon, const QWidget *widget, const int height);
-        QPixmap scaledPixmap(const QString &path, const QWidget *widget, const int height = 0);
-        QPixmap scaledPixmapSvg(const QString &path, const QWidget *widget, const int baseHeight);
+        QPixmap scaledPixmap(const QIcon &icon, const QWidget *widget, int height);
+        QPixmap scaledPixmap(const QString &path, const QWidget *widget, int height = 0);
+        QPixmap scaledPixmapSvg(const QString &path, const QWidget *widget, int baseHeight);
         QSize smallIconSize(const QWidget *widget = nullptr);
         QSize mediumIconSize(const QWidget *widget = nullptr);
         QSize largeIconSize(const QWidget *widget = nullptr);
diff --git a/src/webui/api/appcontroller.cpp b/src/webui/api/appcontroller.cpp
index 1b5990aac..d62942a30 100644
--- a/src/webui/api/appcontroller.cpp
+++ b/src/webui/api/appcontroller.cpp
@@ -89,7 +89,7 @@ void AppController::shutdownAction()
 void AppController::preferencesAction()
 {
     const Preferences *const pref = Preferences::instance();
-    auto session = BitTorrent::Session::instance();
+    const auto *session = BitTorrent::Session::instance();
     QVariantMap data;
 
     // Downloads
@@ -144,7 +144,7 @@ void AppController::preferencesAction()
     data["max_uploads_per_torrent"] = session->maxUploadsPerTorrent();
 
     // Proxy Server
-    auto proxyManager = Net::ProxyConfigurationManager::instance();
+    const auto *proxyManager = Net::ProxyConfigurationManager::instance();
     Net::ProxyConfiguration proxyConf = proxyManager->proxyConfiguration();
     data["proxy_type"] = static_cast<int>(proxyConf.type);
     data["proxy_ip"] = proxyConf.ip;
diff --git a/src/webui/api/searchcontroller.cpp b/src/webui/api/searchcontroller.cpp
index 144167726..0c2597aa2 100644
--- a/src/webui/api/searchcontroller.cpp
+++ b/src/webui/api/searchcontroller.cpp
@@ -109,7 +109,7 @@ void SearchController::stopAction()
     const int id = params()["id"].toInt();
     ISession *const session = sessionManager()->session();
 
-    auto searchHandlers = session->getData<SearchHandlerDict>(SEARCH_HANDLERS);
+    const auto searchHandlers = session->getData<SearchHandlerDict>(SEARCH_HANDLERS);
     if (!searchHandlers.contains(id))
         throw APIError(APIErrorType::NotFound);
 
diff --git a/src/webui/api/searchcontroller.h b/src/webui/api/searchcontroller.h
index 9f3fcd7d9..38cdc40f5 100644
--- a/src/webui/api/searchcontroller.h
+++ b/src/webui/api/searchcontroller.h
@@ -66,8 +66,8 @@ private:
 
     void checkForUpdatesFinished(const QHash<QString, PluginVersion> &updateInfo);
     void checkForUpdatesFailed(const QString &reason);
-    void searchFinished(ISession *session, const int id);
-    void searchFailed(ISession *session, const int id);
+    void searchFinished(ISession *session, int id);
+    void searchFailed(ISession *session, int id);
     int generateSearchId() const;
     QJsonObject getResults(const QList<SearchResult> &searchResults, bool isSearchActive, int totalResults) const;
     QJsonArray getPluginsInfo(const QStringList &plugins) const;
diff --git a/src/webui/api/torrentscontroller.cpp b/src/webui/api/torrentscontroller.cpp
index 6edbe1d31..a46afa2a8 100644
--- a/src/webui/api/torrentscontroller.cpp
+++ b/src/webui/api/torrentscontroller.cpp
@@ -134,7 +134,7 @@ namespace
     QVariantList getStickyTrackers(const BitTorrent::TorrentHandle *const torrent)
     {
         uint seedsDHT = 0, seedsPeX = 0, seedsLSD = 0, leechesDHT = 0, leechesPeX = 0, leechesLSD = 0;
-        for (const BitTorrent::PeerInfo &peer : torrent->peers()) {
+        for (const BitTorrent::PeerInfo &peer : asConst(torrent->peers())) {
             if (peer.isConnecting()) continue;
 
             if (peer.isSeed()) {