Merge #15114: Qt: Replace remaining 0 with nullptr

3a0e76fc12b91b2846d756981e15f09b767a9c37 Replace remaining 0 with nullptr in Qt code (Ben Woosley)
9096276e0b2d5b7e19af9a5f3c144ef108ee55e0 Don't use zero as null pointer constant (-Wzero-as-null-pointer-constant) (practicalswift)

Pull request description:

  This corrects all violations of `-Wzero-as-null-pointer-constant` identified in the Qt codebase.

  These changes are extracted from #15112 as suggested by @MarcoFalke to ease review. This is in service of enabling `-Wzero-as-null-pointer-constant`, which should eliminate this as a concern going forward.

  Note there are 2 non-Qt changes: `src/test/allocator_tests.cpp` and `src/wallet/db.cpp`.

Tree-SHA512: 206bd668802147ba42bc413c2d7d259cb59aca9ec1da74a6bf2ca3932e60ae492faacbc61bcee0fd6b4b49a4d59d075b7e5404f0526b36c47718f9b0587e7768

59 files changed, 119 insertions, 121 deletions

diff --git a/src/qt/addressbookpage.cpp b/src/qt/addressbookpage.cpp
index 26bdf60d4a..726dafccb0 100644
--- a/src/qt/addressbookpage.cpp
+++ b/src/qt/addressbookpage.cpp
@@ -59,7 +59,7 @@ protected:
 AddressBookPage::AddressBookPage(const PlatformStyle *platformStyle, Mode _mode, Tabs _tab, QWidget *parent) :
     QDialog(parent),
     ui(new Ui::AddressBookPage),
-    model(0),
+    model(nullptr),
     mode(_mode),
     tab(_tab)
 {
diff --git a/src/qt/addressbookpage.h b/src/qt/addressbookpage.h
index 32ab2dfeb5..6394d26801 100644
--- a/src/qt/addressbookpage.h
+++ b/src/qt/addressbookpage.h
@@ -38,7 +38,7 @@ public:
         ForEditing  /**< Open address book for editing */
     };
 
-    explicit AddressBookPage(const PlatformStyle *platformStyle, Mode mode, Tabs tab, QWidget *parent = 0);
+    explicit AddressBookPage(const PlatformStyle *platformStyle, Mode mode, Tabs tab, QWidget *parent = nullptr);
     ~AddressBookPage();
 
     void setModel(AddressTableModel *model);
diff --git a/src/qt/addresstablemodel.cpp b/src/qt/addresstablemodel.cpp
index 2f88e15d21..c3143e948a 100644
--- a/src/qt/addresstablemodel.cpp
+++ b/src/qt/addresstablemodel.cpp
@@ -153,7 +153,7 @@ public:
         }
         else
         {
-            return 0;
+            return nullptr;
         }
     }
 };
@@ -300,8 +300,8 @@ QVariant AddressTableModel::headerData(int section, Qt::Orientation orientation,
 
 Qt::ItemFlags AddressTableModel::flags(const QModelIndex &index) const
 {
-    if(!index.isValid())
-        return 0;
+    if (!index.isValid()) return Qt::NoItemFlags;
+
     AddressTableEntry *rec = static_cast<AddressTableEntry*>(index.internalPointer());
 
     Qt::ItemFlags retval = Qt::ItemIsSelectable | Qt::ItemIsEnabled;
diff --git a/src/qt/addresstablemodel.h b/src/qt/addresstablemodel.h
index 41bed4e290..035f3e0571 100644
--- a/src/qt/addresstablemodel.h
+++ b/src/qt/addresstablemodel.h
@@ -25,7 +25,7 @@ class AddressTableModel : public QAbstractTableModel
     Q_OBJECT
 
 public:
-    explicit AddressTableModel(WalletModel *parent = 0);
+    explicit AddressTableModel(WalletModel *parent = nullptr);
     ~AddressTableModel();
 
     enum ColumnIndex {
diff --git a/src/qt/askpassphrasedialog.cpp b/src/qt/askpassphrasedialog.cpp
index 821c23c467..a89a15bc9d 100644
--- a/src/qt/askpassphrasedialog.cpp
+++ b/src/qt/askpassphrasedialog.cpp
@@ -22,7 +22,7 @@ AskPassphraseDialog::AskPassphraseDialog(Mode _mode, QWidget *parent) :
     QDialog(parent),
     ui(new Ui::AskPassphraseDialog),
     mode(_mode),
-    model(0),
+    model(nullptr),
     fCapsLock(false)
 {
     ui->setupUi(this);
diff --git a/src/qt/bantablemodel.cpp b/src/qt/bantablemodel.cpp
index 713db595d5..00c446cc63 100644
--- a/src/qt/bantablemodel.cpp
+++ b/src/qt/bantablemodel.cpp
@@ -76,7 +76,7 @@ public:
         if (idx >= 0 && idx < cachedBanlist.size())
             return &cachedBanlist[idx];
 
-        return 0;
+        return nullptr;
     }
 };
 
@@ -145,8 +145,7 @@ QVariant BanTableModel::headerData(int section, Qt::Orientation orientation, int
 
 Qt::ItemFlags BanTableModel::flags(const QModelIndex &index) const
 {
-    if(!index.isValid())
-        return 0;
+    if (!index.isValid()) return Qt::NoItemFlags;
 
     Qt::ItemFlags retval = Qt::ItemIsSelectable | Qt::ItemIsEnabled;
     return retval;
diff --git a/src/qt/bantablemodel.h b/src/qt/bantablemodel.h
index b8505b599f..9dec5fa6a9 100644
--- a/src/qt/bantablemodel.h
+++ b/src/qt/bantablemodel.h
@@ -45,7 +45,7 @@ class BanTableModel : public QAbstractTableModel
     Q_OBJECT
 
 public:
-    explicit BanTableModel(interfaces::Node& node, ClientModel *parent = 0);
+    explicit BanTableModel(interfaces::Node& node, ClientModel *parent = nullptr);
     ~BanTableModel();
     void startAutoRefresh();
     void stopAutoRefresh();
diff --git a/src/qt/bitcoin.cpp b/src/qt/bitcoin.cpp
index 6e08dae3c4..893dda1601 100644
--- a/src/qt/bitcoin.cpp
+++ b/src/qt/bitcoin.cpp
@@ -178,18 +178,18 @@ void BitcoinCore::shutdown()
 
 BitcoinApplication::BitcoinApplication(interfaces::Node& node, int &argc, char **argv):
     QApplication(argc, argv),
-    coreThread(0),
+    coreThread(nullptr),
     m_node(node),
-    optionsModel(0),
-    clientModel(0),
-    window(0),
-    pollShutdownTimer(0),
+    optionsModel(nullptr),
+    clientModel(nullptr),
+    window(nullptr),
+    pollShutdownTimer(nullptr),
 #ifdef ENABLE_WALLET
-    paymentServer(0),
+    paymentServer(nullptr),
     m_wallet_models(),
 #endif
     returnValue(0),
-    platformStyle(0)
+    platformStyle(nullptr)
 {
     setQuitOnLastWindowClosed(false);
 }
@@ -218,15 +218,15 @@ BitcoinApplication::~BitcoinApplication()
     }
 
     delete window;
-    window = 0;
+    window = nullptr;
 #ifdef ENABLE_WALLET
     delete paymentServer;
-    paymentServer = 0;
+    paymentServer = nullptr;
 #endif
     delete optionsModel;
-    optionsModel = 0;
+    optionsModel = nullptr;
     delete platformStyle;
-    platformStyle = 0;
+    platformStyle = nullptr;
 }
 
 #ifdef ENABLE_WALLET
@@ -243,7 +243,7 @@ void BitcoinApplication::createOptionsModel(bool resetSettings)
 
 void BitcoinApplication::createWindow(const NetworkStyle *networkStyle)
 {
-    window = new BitcoinGUI(m_node, platformStyle, networkStyle, 0);
+    window = new BitcoinGUI(m_node, platformStyle, networkStyle, nullptr);
 
     pollShutdownTimer = new QTimer(window);
     connect(pollShutdownTimer, &QTimer::timeout, window, &BitcoinGUI::detectShutdown);
@@ -251,7 +251,7 @@ void BitcoinApplication::createWindow(const NetworkStyle *networkStyle)
 
 void BitcoinApplication::createSplashScreen(const NetworkStyle *networkStyle)
 {
-    SplashScreen *splash = new SplashScreen(m_node, 0, networkStyle);
+    SplashScreen *splash = new SplashScreen(m_node, nullptr, networkStyle);
     // We don't hold a direct pointer to the splash screen after creation, but the splash
     // screen will take care of deleting itself when finish() happens.
     splash->show();
@@ -312,7 +312,7 @@ void BitcoinApplication::requestShutdown()
     qDebug() << __func__ << ": Requesting shutdown";
     startThread();
     window->hide();
-    window->setClientModel(0);
+    window->setClientModel(nullptr);
     pollShutdownTimer->stop();
 
 #ifdef ENABLE_WALLET
@@ -323,7 +323,7 @@ void BitcoinApplication::requestShutdown()
     m_wallet_models.clear();
 #endif
     delete clientModel;
-    clientModel = 0;
+    clientModel = nullptr;
 
     m_node.startShutdown();
 
@@ -429,7 +429,7 @@ void BitcoinApplication::shutdownResult()
 
 void BitcoinApplication::handleRunawayException(const QString &message)
 {
-    QMessageBox::critical(0, "Runaway exception", BitcoinGUI::tr("A fatal error occurred. Bitcoin can no longer continue safely and will quit.") + QString("\n\n") + message);
+    QMessageBox::critical(nullptr, "Runaway exception", BitcoinGUI::tr("A fatal error occurred. Bitcoin can no longer continue safely and will quit.") + QString("\n\n") + message);
     ::exit(EXIT_FAILURE);
 }
 
@@ -503,7 +503,7 @@ int GuiMain(int argc, char* argv[])
     SetupUIArgs();
     std::string error;
     if (!node->parseParameters(argc, argv, error)) {
-        QMessageBox::critical(0, QObject::tr(PACKAGE_NAME),
+        QMessageBox::critical(nullptr, QObject::tr(PACKAGE_NAME),
             QObject::tr("Error parsing command line arguments: %1.").arg(QString::fromStdString(error)));
         return EXIT_FAILURE;
     }
@@ -540,12 +540,12 @@ int GuiMain(int argc, char* argv[])
     /// - Do not call GetDataDir(true) before this step finishes
     if (!fs::is_directory(GetDataDir(false)))
     {
-        QMessageBox::critical(0, QObject::tr(PACKAGE_NAME),
-                              QObject::tr("Error: Specified data directory \"%1\" does not exist.").arg(QString::fromStdString(gArgs.GetArg("-datadir", ""))));
+        QMessageBox::critical(nullptr, QObject::tr(PACKAGE_NAME),
+            QObject::tr("Error: Specified data directory \"%1\" does not exist.").arg(QString::fromStdString(gArgs.GetArg("-datadir", ""))));
         return EXIT_FAILURE;
     }
     if (!node->readConfigFiles(error)) {
-        QMessageBox::critical(0, QObject::tr(PACKAGE_NAME),
+        QMessageBox::critical(nullptr, QObject::tr(PACKAGE_NAME),
             QObject::tr("Error: Cannot parse configuration file: %1.").arg(QString::fromStdString(error)));
         return EXIT_FAILURE;
     }
@@ -560,7 +560,7 @@ int GuiMain(int argc, char* argv[])
     try {
         node->selectParams(gArgs.GetChainName());
     } catch(std::exception &e) {
-        QMessageBox::critical(0, QObject::tr(PACKAGE_NAME), QObject::tr("Error: %1").arg(e.what()));
+        QMessageBox::critical(nullptr, QObject::tr(PACKAGE_NAME), QObject::tr("Error: %1").arg(e.what()));
         return EXIT_FAILURE;
     }
 #ifdef ENABLE_WALLET
diff --git a/src/qt/bitcoinamountfield.cpp b/src/qt/bitcoinamountfield.cpp
index 558fcf50ba..5854ade655 100644
--- a/src/qt/bitcoinamountfield.cpp
+++ b/src/qt/bitcoinamountfield.cpp
@@ -60,7 +60,7 @@ public:
         }
     }
 
-    CAmount value(bool *valid_out=0) const
+    CAmount value(bool *valid_out=nullptr) const
     {
         return parse(text(), valid_out);
     }
@@ -159,7 +159,7 @@ private:
      * return validity.
      * @note Must return 0 if !valid.
      */
-    CAmount parse(const QString &text, bool *valid_out=0) const
+    CAmount parse(const QString &text, bool *valid_out=nullptr) const
     {
         CAmount val = 0;
         bool valid = BitcoinUnits::parse(currentUnit, text, &val);
@@ -196,7 +196,7 @@ protected:
         if (text().isEmpty()) // Allow step-up with empty field
             return StepUpEnabled;
 
-        StepEnabled rv = 0;
+        StepEnabled rv = StepNone;
         bool valid = false;
         CAmount val = value(&valid);
         if (valid) {
@@ -216,7 +216,7 @@ Q_SIGNALS:
 
 BitcoinAmountField::BitcoinAmountField(QWidget *parent) :
     QWidget(parent),
-    amount(0)
+    amount(nullptr)
 {
     amount = new AmountSpinBox(this);
     amount->setLocale(QLocale::c());
diff --git a/src/qt/bitcoinamountfield.h b/src/qt/bitcoinamountfield.h
index 650481e30d..2db6b65f2c 100644
--- a/src/qt/bitcoinamountfield.h
+++ b/src/qt/bitcoinamountfield.h
@@ -26,9 +26,9 @@ class BitcoinAmountField: public QWidget
     Q_PROPERTY(qint64 value READ value WRITE setValue NOTIFY valueChanged USER true)
 
 public:
-    explicit BitcoinAmountField(QWidget *parent = 0);
+    explicit BitcoinAmountField(QWidget *parent = nullptr);
 
-    CAmount value(bool *value=0) const;
+    CAmount value(bool *value=nullptr) const;
     void setValue(const CAmount& value);
 
     /** If allow empty is set to false the field will be set to the minimum allowed value if left empty. **/
diff --git a/src/qt/bitcoingui.cpp b/src/qt/bitcoingui.cpp
index 155f8efe7f..77130c8c63 100644
--- a/src/qt/bitcoingui.cpp
+++ b/src/qt/bitcoingui.cpp
@@ -95,7 +95,7 @@ BitcoinGUI::BitcoinGUI(interfaces::Node& node, const PlatformStyle *_platformSty
     setWindowIcon(networkStyle->getTrayAndWindowIcon());
     setWindowTitle(windowTitle);
 
-    rpcConsole = new RPCConsole(node, _platformStyle, 0);
+    rpcConsole = new RPCConsole(node, _platformStyle, nullptr);
     helpMessageDialog = new HelpMessageDialog(node, this, false);
 #ifdef ENABLE_WALLET
     if(enableWallet)
@@ -1196,7 +1196,7 @@ void BitcoinGUI::updateProxyIcon()
     bool proxy_enabled = clientModel->getProxyInfo(ip_port);
 
     if (proxy_enabled) {
-        if (labelProxyIcon->pixmap() == 0) {
+        if (labelProxyIcon->pixmap() == nullptr) {
             QString ip_port_q = QString::fromStdString(ip_port);
             labelProxyIcon->setPixmap(platformStyle->SingleColorIcon(":/icons/proxy").pixmap(STATUSBAR_ICONSIZE, STATUSBAR_ICONSIZE));
             labelProxyIcon->setToolTip(tr("Proxy is <b>enabled</b>: %1").arg(ip_port_q));
@@ -1242,7 +1242,7 @@ void BitcoinGUI::showProgress(const QString &title, int nProgress)
         progressDialog = new QProgressDialog(title, "", 0, 100);
         progressDialog->setWindowModality(Qt::ApplicationModal);
         progressDialog->setMinimumDuration(0);
-        progressDialog->setCancelButton(0);
+        progressDialog->setCancelButton(nullptr);
         progressDialog->setAutoClose(false);
         progressDialog->setValue(0);
     }
@@ -1304,8 +1304,8 @@ void BitcoinGUI::unsubscribeFromCoreSignals()
 }
 
 UnitDisplayStatusBarControl::UnitDisplayStatusBarControl(const PlatformStyle *platformStyle) :
-    optionsModel(0),
-    menu(0)
+    optionsModel(nullptr),
+    menu(nullptr)
 {
     createContextMenu();
     setToolTip(tr("Unit to show amounts in. Click to select another unit."));
diff --git a/src/qt/bitcoingui.h b/src/qt/bitcoingui.h
index 9ca9e4c926..48e96d6169 100644
--- a/src/qt/bitcoingui.h
+++ b/src/qt/bitcoingui.h
@@ -67,7 +67,7 @@ class BitcoinGUI : public QMainWindow
 public:
     static const std::string DEFAULT_UIPLATFORM;
 
-    explicit BitcoinGUI(interfaces::Node& node, const PlatformStyle *platformStyle, const NetworkStyle *networkStyle, QWidget *parent = 0);
+    explicit BitcoinGUI(interfaces::Node& node, const PlatformStyle *platformStyle, const NetworkStyle *networkStyle, QWidget *parent = nullptr);
     ~BitcoinGUI();
 
     /** Set the client model.
diff --git a/src/qt/clientmodel.cpp b/src/qt/clientmodel.cpp
index 217326f818..30d9e977b8 100644
--- a/src/qt/clientmodel.cpp
+++ b/src/qt/clientmodel.cpp
@@ -35,9 +35,9 @@ ClientModel::ClientModel(interfaces::Node& node, OptionsModel *_optionsModel, QO
     QObject(parent),
     m_node(node),
     optionsModel(_optionsModel),
-    peerTableModel(0),
-    banTableModel(0),
-    pollTimer(0)
+    peerTableModel(nullptr),
+    banTableModel(nullptr),
+    pollTimer(nullptr)
 {
     cachedBestHeaderHeight = -1;
     cachedBestHeaderTime = -1;
diff --git a/src/qt/clientmodel.h b/src/qt/clientmodel.h
index 79e7074cca..95f4521f06 100644
--- a/src/qt/clientmodel.h
+++ b/src/qt/clientmodel.h
@@ -46,7 +46,7 @@ class ClientModel : public QObject
     Q_OBJECT
 
 public:
-    explicit ClientModel(interfaces::Node& node, OptionsModel *optionsModel, QObject *parent = 0);
+    explicit ClientModel(interfaces::Node& node, OptionsModel *optionsModel, QObject *parent = nullptr);
     ~ClientModel();
 
     interfaces::Node& node() const { return m_node; }
diff --git a/src/qt/coincontroldialog.cpp b/src/qt/coincontroldialog.cpp
index 77f8bcf901..0d9f1adcd2 100644
--- a/src/qt/coincontroldialog.cpp
+++ b/src/qt/coincontroldialog.cpp
@@ -49,7 +49,7 @@ bool CCoinControlWidgetItem::operator<(const QTreeWidgetItem &other) const {
 CoinControlDialog::CoinControlDialog(const PlatformStyle *_platformStyle, QWidget *parent) :
     QDialog(parent),
     ui(new Ui::CoinControlDialog),
-    model(0),
+    model(nullptr),
     platformStyle(_platformStyle)
 {
     ui->setupUi(this);
diff --git a/src/qt/coincontroldialog.h b/src/qt/coincontroldialog.h
index 8f15ae4b20..efc06a7656 100644
--- a/src/qt/coincontroldialog.h
+++ b/src/qt/coincontroldialog.h
@@ -43,7 +43,7 @@ class CoinControlDialog : public QDialog
     Q_OBJECT
 
 public:
-    explicit CoinControlDialog(const PlatformStyle *platformStyle, QWidget *parent = 0);
+    explicit CoinControlDialog(const PlatformStyle *platformStyle, QWidget *parent = nullptr);
     ~CoinControlDialog();
 
     void setModel(WalletModel *model);
diff --git a/src/qt/coincontroltreewidget.h b/src/qt/coincontroltreewidget.h
index 62645fcdb0..88fc8b704f 100644
--- a/src/qt/coincontroltreewidget.h
+++ b/src/qt/coincontroltreewidget.h
@@ -13,7 +13,7 @@ class CoinControlTreeWidget : public QTreeWidget
     Q_OBJECT
 
 public:
-    explicit CoinControlTreeWidget(QWidget *parent = 0);
+    explicit CoinControlTreeWidget(QWidget *parent = nullptr);
 
 protected:
     virtual void keyPressEvent(QKeyEvent *event);
diff --git a/src/qt/csvmodelwriter.cpp b/src/qt/csvmodelwriter.cpp
index fe63fed52c..656afb6e87 100644
--- a/src/qt/csvmodelwriter.cpp
+++ b/src/qt/csvmodelwriter.cpp
@@ -10,7 +10,7 @@
 
 CSVModelWriter::CSVModelWriter(const QString &_filename, QObject *parent) :
     QObject(parent),
-    filename(_filename), model(0)
+    filename(_filename), model(nullptr)
 {
 }
 
diff --git a/src/qt/csvmodelwriter.h b/src/qt/csvmodelwriter.h
index edea369ad1..e8611bea35 100644
--- a/src/qt/csvmodelwriter.h
+++ b/src/qt/csvmodelwriter.h
@@ -20,7 +20,7 @@ class CSVModelWriter : public QObject
     Q_OBJECT
 
 public:
-    explicit CSVModelWriter(const QString &filename, QObject *parent = 0);
+    explicit CSVModelWriter(const QString &filename, QObject *parent = nullptr);
 
     void setModel(const QAbstractItemModel *model);
     void addColumn(const QString &title, int column, int role=Qt::EditRole);
diff --git a/src/qt/editaddressdialog.cpp b/src/qt/editaddressdialog.cpp
index 0b0b96b30c..4711412ac4 100644
--- a/src/qt/editaddressdialog.cpp
+++ b/src/qt/editaddressdialog.cpp
@@ -15,9 +15,9 @@
 EditAddressDialog::EditAddressDialog(Mode _mode, QWidget *parent) :
     QDialog(parent),
     ui(new Ui::EditAddressDialog),
-    mapper(0),
+    mapper(nullptr),
     mode(_mode),
-    model(0)
+    model(nullptr)
 {
     ui->setupUi(this);
 
diff --git a/src/qt/editaddressdialog.h b/src/qt/editaddressdialog.h
index fd88b45793..4d0e0709be 100644
--- a/src/qt/editaddressdialog.h
+++ b/src/qt/editaddressdialog.h
@@ -30,7 +30,7 @@ public:
         EditSendingAddress
     };
 
-    explicit EditAddressDialog(Mode mode, QWidget *parent = 0);
+    explicit EditAddressDialog(Mode mode, QWidget *parent = nullptr);
     ~EditAddressDialog();
 
     void setModel(AddressTableModel *model);
diff --git a/src/qt/guiutil.h b/src/qt/guiutil.h
index f1d0aa48ef..ecb770d147 100644
--- a/src/qt/guiutil.h
+++ b/src/qt/guiutil.h
@@ -133,7 +133,7 @@ namespace GUIUtil
         Q_OBJECT
 
     public:
-        explicit ToolTipToRichTextFilter(int size_threshold, QObject *parent = 0);
+        explicit ToolTipToRichTextFilter(int size_threshold, QObject *parent = nullptr);
 
     protected:
         bool eventFilter(QObject *obj, QEvent *evt);
diff --git a/src/qt/intro.cpp b/src/qt/intro.cpp
index a9a6ab9a8e..fa9a50b1ed 100644
--- a/src/qt/intro.cpp
+++ b/src/qt/intro.cpp
@@ -113,7 +113,7 @@ void FreespaceChecker::check()
 Intro::Intro(QWidget *parent, uint64_t blockchain_size, uint64_t chain_state_size) :
     QDialog(parent),
     ui(new Ui::Intro),
-    thread(0),
+    thread(nullptr),
     signalled(false),
     m_blockchain_size(blockchain_size),
     m_chain_state_size(chain_state_size)
@@ -226,7 +226,7 @@ bool Intro::pickDataDirectory(interfaces::Node& node)
                 }
                 break;
             } catch (const fs::filesystem_error&) {
-                QMessageBox::critical(0, tr(PACKAGE_NAME),
+                QMessageBox::critical(nullptr, tr(PACKAGE_NAME),
                     tr("Error: Specified data directory \"%1\" cannot be created.").arg(dataDir));
                 /* fall through, back to choosing screen */
             }
@@ -286,7 +286,7 @@ void Intro::on_dataDirectory_textChanged(const QString &dataDirStr)
 
 void Intro::on_ellipsisButton_clicked()
 {
-    QString dir = QDir::toNativeSeparators(QFileDialog::getExistingDirectory(0, "Choose data directory", ui->dataDirectory->text()));
+    QString dir = QDir::toNativeSeparators(QFileDialog::getExistingDirectory(nullptr, "Choose data directory", ui->dataDirectory->text()));
     if(!dir.isEmpty())
         ui->dataDirectory->setText(dir);
 }
diff --git a/src/qt/intro.h b/src/qt/intro.h
index 01c4165f3e..3da8a16114 100644
--- a/src/qt/intro.h
+++ b/src/qt/intro.h
@@ -30,7 +30,7 @@ class Intro : public QDialog
     Q_OBJECT
 
 public:
-    explicit Intro(QWidget *parent = 0,
+    explicit Intro(QWidget *parent = nullptr,
                    uint64_t blockchain_size = 0, uint64_t chain_state_size = 0);
     ~Intro();
 
diff --git a/src/qt/networkstyle.cpp b/src/qt/networkstyle.cpp
index da048d3211..f0c860e669 100644
--- a/src/qt/networkstyle.cpp
+++ b/src/qt/networkstyle.cpp
@@ -88,5 +88,5 @@ const NetworkStyle *NetworkStyle::instantiate(const QString &networkId)
                     network_styles[x].titleAddText);
         }
     }
-    return 0;
+    return nullptr;
 }
diff --git a/src/qt/optionsdialog.cpp b/src/qt/optionsdialog.cpp
index c9871f6c66..27cec06d4b 100644
--- a/src/qt/optionsdialog.cpp
+++ b/src/qt/optionsdialog.cpp
@@ -29,8 +29,8 @@
 OptionsDialog::OptionsDialog(QWidget *parent, bool enableWallet) :
     QDialog(parent),
     ui(new Ui::OptionsDialog),
-    model(0),
-    mapper(0)
+    model(nullptr),
+    mapper(nullptr)
 {
     ui->setupUi(this);
 
diff --git a/src/qt/optionsmodel.h b/src/qt/optionsmodel.h
index 2421734527..1af3a72b92 100644
--- a/src/qt/optionsmodel.h
+++ b/src/qt/optionsmodel.h
@@ -31,7 +31,7 @@ class OptionsModel : public QAbstractListModel
     Q_OBJECT
 
 public:
-    explicit OptionsModel(interfaces::Node& node, QObject *parent = 0, bool resetSettings = false);
+    explicit OptionsModel(interfaces::Node& node, QObject *parent = nullptr, bool resetSettings = false);
 
     enum OptionID {
         StartAtStartup,         // bool
diff --git a/src/qt/overviewpage.cpp b/src/qt/overviewpage.cpp
index bec79335e7..d8e48f350a 100644
--- a/src/qt/overviewpage.cpp
+++ b/src/qt/overviewpage.cpp
@@ -113,8 +113,8 @@ public:
 OverviewPage::OverviewPage(const PlatformStyle *platformStyle, QWidget *parent) :
     QWidget(parent),
     ui(new Ui::OverviewPage),
-    clientModel(0),
-    walletModel(0),
+    clientModel(nullptr),
+    walletModel(nullptr),
     txdelegate(new TxViewDelegate(platformStyle, this))
 {
     ui->setupUi(this);
diff --git a/src/qt/overviewpage.h b/src/qt/overviewpage.h
index 75100ae6f7..00ba7ad4ce 100644
--- a/src/qt/overviewpage.h
+++ b/src/qt/overviewpage.h
@@ -30,7 +30,7 @@ class OverviewPage : public QWidget
     Q_OBJECT
 
 public:
-    explicit OverviewPage(const PlatformStyle *platformStyle, QWidget *parent = 0);
+    explicit OverviewPage(const PlatformStyle *platformStyle, QWidget *parent = nullptr);
     ~OverviewPage();
 
     void setClientModel(ClientModel *clientModel);
diff --git a/src/qt/paymentserver.cpp b/src/qt/paymentserver.cpp
index 8148986b51..b1ec90ad36 100644
--- a/src/qt/paymentserver.cpp
+++ b/src/qt/paymentserver.cpp
@@ -194,10 +194,10 @@ bool PaymentServer::ipcSendCommandLine()
 PaymentServer::PaymentServer(QObject* parent, bool startLocalServer) :
     QObject(parent),
     saveURIs(true),
-    uriServer(0),
-    optionsModel(0)
+    uriServer(nullptr),
+    optionsModel(nullptr)
 #ifdef ENABLE_BIP70
-    ,netManager(0)
+    ,netManager(nullptr)
 #endif
 {
 #ifdef ENABLE_BIP70
@@ -223,7 +223,7 @@ PaymentServer::PaymentServer(QObject* parent, bool startLocalServer) :
 
         if (!uriServer->listen(name)) {
             // constructor is called early in init, so don't use "Q_EMIT message()" here
-            QMessageBox::critical(0, tr("Payment request error"),
+            QMessageBox::critical(nullptr, tr("Payment request error"),
                 tr("Cannot start bitcoin: click-to-pay handler"));
         }
         else {
diff --git a/src/qt/peertablemodel.cpp b/src/qt/peertablemodel.cpp
index e2e78fe81b..496aeebf7d 100644
--- a/src/qt/peertablemodel.cpp
+++ b/src/qt/peertablemodel.cpp
@@ -96,7 +96,7 @@ public:
         if (idx >= 0 && idx < cachedNodeStats.size())
             return &cachedNodeStats[idx];
 
-        return 0;
+        return nullptr;
     }
 };
 
@@ -104,7 +104,7 @@ PeerTableModel::PeerTableModel(interfaces::Node& node, ClientModel *parent) :
     QAbstractTableModel(parent),
     m_node(node),
     clientModel(parent),
-    timer(0)
+    timer(nullptr)
 {
     columns << tr("NodeId") << tr("Node/Service") << tr("Ping") << tr("Sent") << tr("Received") << tr("User Agent");
     priv.reset(new PeerTablePriv());
@@ -197,8 +197,7 @@ QVariant PeerTableModel::headerData(int section, Qt::Orientation orientation, in
 
 Qt::ItemFlags PeerTableModel::flags(const QModelIndex &index) const
 {
-    if(!index.isValid())
-        return 0;
+    if (!index.isValid()) return Qt::NoItemFlags;
 
     Qt::ItemFlags retval = Qt::ItemIsSelectable | Qt::ItemIsEnabled;
     return retval;
diff --git a/src/qt/peertablemodel.h b/src/qt/peertablemodel.h
index 738a06496f..b3f5dd7dbe 100644
--- a/src/qt/peertablemodel.h
+++ b/src/qt/peertablemodel.h
@@ -51,7 +51,7 @@ class PeerTableModel : public QAbstractTableModel
     Q_OBJECT
 
 public:
-    explicit PeerTableModel(interfaces::Node& node, ClientModel *parent = 0);
+    explicit PeerTableModel(interfaces::Node& node, ClientModel *parent = nullptr);
     ~PeerTableModel();
     const CNodeCombinedStats *getNodeStats(int idx);
     int getRowByNodeId(NodeId nodeid);
diff --git a/src/qt/platformstyle.cpp b/src/qt/platformstyle.cpp
index 56e0830cdc..d537d759de 100644
--- a/src/qt/platformstyle.cpp
+++ b/src/qt/platformstyle.cpp
@@ -139,6 +139,6 @@ const PlatformStyle *PlatformStyle::instantiate(const QString &platformId)
                     platform_styles[x].useExtraSpacing);
         }
     }
-    return 0;
+    return nullptr;
 }
 
diff --git a/src/qt/qvalidatedlineedit.cpp b/src/qt/qvalidatedlineedit.cpp
index 85c5a58a84..aa936d6b7c 100644
--- a/src/qt/qvalidatedlineedit.cpp
+++ b/src/qt/qvalidatedlineedit.cpp
@@ -10,7 +10,7 @@
 QValidatedLineEdit::QValidatedLineEdit(QWidget *parent) :
     QLineEdit(parent),
     valid(true),
-    checkValidator(0)
+    checkValidator(nullptr)
 {
     connect(this, &QValidatedLineEdit::textChanged, this, &QValidatedLineEdit::markValid);
 }
diff --git a/src/qt/qvaluecombobox.h b/src/qt/qvaluecombobox.h
index f266302310..8892071fba 100644
--- a/src/qt/qvaluecombobox.h
+++ b/src/qt/qvaluecombobox.h
@@ -16,7 +16,7 @@ class QValueComboBox : public QComboBox
     Q_PROPERTY(QVariant value READ value WRITE setValue NOTIFY valueChanged USER true)
 
 public:
-    explicit QValueComboBox(QWidget *parent = 0);
+    explicit QValueComboBox(QWidget *parent = nullptr);
 
     QVariant value() const;
     void setValue(const QVariant &value);
diff --git a/src/qt/receivecoinsdialog.cpp b/src/qt/receivecoinsdialog.cpp
index a7cc5da19e..bc96b5a6f7 100644
--- a/src/qt/receivecoinsdialog.cpp
+++ b/src/qt/receivecoinsdialog.cpp
@@ -25,8 +25,8 @@
 ReceiveCoinsDialog::ReceiveCoinsDialog(const PlatformStyle *_platformStyle, QWidget *parent) :
     QDialog(parent),
     ui(new Ui::ReceiveCoinsDialog),
-    columnResizingFixer(0),
-    model(0),
+    columnResizingFixer(nullptr),
+    model(nullptr),
     platformStyle(_platformStyle)
 {
     ui->setupUi(this);
diff --git a/src/qt/receivecoinsdialog.h b/src/qt/receivecoinsdialog.h
index bc0f6248f0..5bca2f46e2 100644
--- a/src/qt/receivecoinsdialog.h
+++ b/src/qt/receivecoinsdialog.h
@@ -39,7 +39,7 @@ public:
         MINIMUM_COLUMN_WIDTH = 130
     };
 
-    explicit ReceiveCoinsDialog(const PlatformStyle *platformStyle, QWidget *parent = 0);
+    explicit ReceiveCoinsDialog(const PlatformStyle *platformStyle, QWidget *parent = nullptr);
     ~ReceiveCoinsDialog();
 
     void setModel(WalletModel *model);
diff --git a/src/qt/receiverequestdialog.cpp b/src/qt/receiverequestdialog.cpp
index c561d948be..f5b30cf6d2 100644
--- a/src/qt/receiverequestdialog.cpp
+++ b/src/qt/receiverequestdialog.cpp
@@ -26,7 +26,7 @@
 #endif
 
 QRImageWidget::QRImageWidget(QWidget *parent):
-    QLabel(parent), contextMenu(0)
+    QLabel(parent), contextMenu(nullptr)
 {
     contextMenu = new QMenu(this);
     QAction *saveImageAction = new QAction(tr("&Save Image..."), this);
@@ -88,7 +88,7 @@ void QRImageWidget::contextMenuEvent(QContextMenuEvent *event)
 ReceiveRequestDialog::ReceiveRequestDialog(QWidget *parent) :
     QDialog(parent),
     ui(new Ui::ReceiveRequestDialog),
-    model(0)
+    model(nullptr)
 {
     ui->setupUi(this);
 
diff --git a/src/qt/receiverequestdialog.h b/src/qt/receiverequestdialog.h
index 5662af18b7..dd28fd73c8 100644
--- a/src/qt/receiverequestdialog.h
+++ b/src/qt/receiverequestdialog.h
@@ -28,7 +28,7 @@ class QRImageWidget : public QLabel
     Q_OBJECT
 
 public:
-    explicit QRImageWidget(QWidget *parent = 0);
+    explicit QRImageWidget(QWidget *parent = nullptr);
     QImage exportImage();
 
 public Q_SLOTS:
@@ -48,7 +48,7 @@ class ReceiveRequestDialog : public QDialog
     Q_OBJECT
 
 public:
-    explicit ReceiveRequestDialog(QWidget *parent = 0);
+    explicit ReceiveRequestDialog(QWidget *parent = nullptr);
     ~ReceiveRequestDialog();
 
     void setModel(WalletModel *model);
diff --git a/src/qt/rpcconsole.cpp b/src/qt/rpcconsole.cpp
index d062ea49bd..3d7211aca2 100644
--- a/src/qt/rpcconsole.cpp
+++ b/src/qt/rpcconsole.cpp
@@ -485,7 +485,7 @@ RPCConsole::RPCConsole(interfaces::Node& node, const PlatformStyle *_platformSty
 
     // set library version labels
 #ifdef ENABLE_WALLET
-    ui->berkeleyDBVersion->setText(DbEnv::version(0, 0, 0));
+    ui->berkeleyDBVersion->setText(DbEnv::version(nullptr, nullptr, nullptr));
 #else
     ui->label_berkeleyDBVersion->hide();
     ui->berkeleyDBVersion->hide();
diff --git a/src/qt/sendcoinsdialog.cpp b/src/qt/sendcoinsdialog.cpp
index 65db0280b7..6e00ab755c 100644
--- a/src/qt/sendcoinsdialog.cpp
+++ b/src/qt/sendcoinsdialog.cpp
@@ -54,8 +54,8 @@ int getIndexForConfTarget(int target) {
 SendCoinsDialog::SendCoinsDialog(const PlatformStyle *_platformStyle, QWidget *parent) :
     QDialog(parent),
     ui(new Ui::SendCoinsDialog),
-    clientModel(0),
-    model(0),
+    clientModel(nullptr),
+    model(nullptr),
     fNewRecipientAllowed(true),
     fFeeMinimized(true),
     platformStyle(_platformStyle)
@@ -443,7 +443,7 @@ SendCoinsEntry *SendCoinsDialog::addEntry()
 
 void SendCoinsDialog::updateTabsAndLabels()
 {
-    setupTabChain(0);
+    setupTabChain(nullptr);
     coinControlUpdateLabels();
 }
 
@@ -478,7 +478,7 @@ QWidget *SendCoinsDialog::setupTabChain(QWidget *prev)
 
 void SendCoinsDialog::setAddress(const QString &address)
 {
-    SendCoinsEntry *entry = 0;
+    SendCoinsEntry *entry = nullptr;
     // Replace the first entry if it is still unused
     if(ui->entries->count() == 1)
     {
@@ -501,7 +501,7 @@ void SendCoinsDialog::pasteEntry(const SendCoinsRecipient &rv)
     if(!fNewRecipientAllowed)
         return;
 
-    SendCoinsEntry *entry = 0;
+    SendCoinsEntry *entry = nullptr;
     // Replace the first entry if it is still unused
     if(ui->entries->count() == 1)
     {
diff --git a/src/qt/sendcoinsdialog.h b/src/qt/sendcoinsdialog.h
index e1ebc77d59..337a72b878 100644
--- a/src/qt/sendcoinsdialog.h
+++ b/src/qt/sendcoinsdialog.h
@@ -31,7 +31,7 @@ class SendCoinsDialog : public QDialog
     Q_OBJECT
 
 public:
-    explicit SendCoinsDialog(const PlatformStyle *platformStyle, QWidget *parent = 0);
+    explicit SendCoinsDialog(const PlatformStyle *platformStyle, QWidget *parent = nullptr);
     ~SendCoinsDialog();
 
     void setClientModel(ClientModel *clientModel);
@@ -108,7 +108,7 @@ class SendConfirmationDialog : public QMessageBox
     Q_OBJECT
 
 public:
-    SendConfirmationDialog(const QString &title, const QString &text, int secDelay = SEND_CONFIRM_DELAY, QWidget *parent = 0);
+    SendConfirmationDialog(const QString &title, const QString &text, int secDelay = SEND_CONFIRM_DELAY, QWidget *parent = nullptr);
     int exec();
 
 private Q_SLOTS:
diff --git a/src/qt/sendcoinsentry.cpp b/src/qt/sendcoinsentry.cpp
index 76c942c8b9..7324d759fb 100644
--- a/src/qt/sendcoinsentry.cpp
+++ b/src/qt/sendcoinsentry.cpp
@@ -21,7 +21,7 @@
 SendCoinsEntry::SendCoinsEntry(const PlatformStyle *_platformStyle, QWidget *parent) :
     QStackedWidget(parent),
     ui(new Ui::SendCoinsEntry),
-    model(0),
+    model(nullptr),
     platformStyle(_platformStyle)
 {
     ui->setupUi(this);
@@ -155,7 +155,7 @@ bool SendCoinsEntry::validate(interfaces::Node& node)
     }
 
     // Sending a zero amount is invalid
-    if (ui->payAmount->value(0) <= 0)
+    if (ui->payAmount->value(nullptr) <= 0)
     {
         ui->payAmount->setValid(false);
         retval = false;
diff --git a/src/qt/sendcoinsentry.h b/src/qt/sendcoinsentry.h
index 48ecd598d6..42e2217130 100644
--- a/src/qt/sendcoinsentry.h
+++ b/src/qt/sendcoinsentry.h
@@ -26,7 +26,7 @@ class SendCoinsEntry : public QStackedWidget
     Q_OBJECT
 
 public:
-    explicit SendCoinsEntry(const PlatformStyle *platformStyle, QWidget *parent = 0);
+    explicit SendCoinsEntry(const PlatformStyle *platformStyle, QWidget *parent = nullptr);
     ~SendCoinsEntry();
 
     void setModel(WalletModel *model);
diff --git a/src/qt/signverifymessagedialog.cpp b/src/qt/signverifymessagedialog.cpp
index 487fc9ee1e..d37a78fa8c 100644
--- a/src/qt/signverifymessagedialog.cpp
+++ b/src/qt/signverifymessagedialog.cpp
@@ -22,7 +22,7 @@
 SignVerifyMessageDialog::SignVerifyMessageDialog(const PlatformStyle *_platformStyle, QWidget *parent) :
     QDialog(parent),
     ui(new Ui::SignVerifyMessageDialog),
-    model(0),
+    model(nullptr),
     platformStyle(_platformStyle)
 {
     ui->setupUi(this);
diff --git a/src/qt/splashscreen.cpp b/src/qt/splashscreen.cpp
index b109a08b1c..0126a2920e 100644
--- a/src/qt/splashscreen.cpp
+++ b/src/qt/splashscreen.cpp
@@ -26,7 +26,7 @@
 
 
 SplashScreen::SplashScreen(interfaces::Node& node, Qt::WindowFlags f, const NetworkStyle *networkStyle) :
-    QWidget(0, f), curAlignment(0), m_node(node)
+    QWidget(nullptr, f), curAlignment(0), m_node(node)
 {
     // set reference point, paddings
     int paddingRight            = 50;
diff --git a/src/qt/trafficgraphwidget.cpp b/src/qt/trafficgraphwidget.cpp
index 3aed3f2b97..1588be8da3 100644
--- a/src/qt/trafficgraphwidget.cpp
+++ b/src/qt/trafficgraphwidget.cpp
@@ -19,14 +19,14 @@
 
 TrafficGraphWidget::TrafficGraphWidget(QWidget *parent) :
     QWidget(parent),
-    timer(0),
+    timer(nullptr),
     fMax(0.0f),
     nMins(0),
     vSamplesIn(),
     vSamplesOut(),
     nLastBytesIn(0),
     nLastBytesOut(0),
-    clientModel(0)
+    clientModel(nullptr)
 {
     timer = new QTimer(this);
     connect(timer, &QTimer::timeout, this, &TrafficGraphWidget::updateRates);
diff --git a/src/qt/trafficgraphwidget.h b/src/qt/trafficgraphwidget.h
index 00660574af..48bd246b34 100644
--- a/src/qt/trafficgraphwidget.h
+++ b/src/qt/trafficgraphwidget.h
@@ -20,7 +20,7 @@ class TrafficGraphWidget : public QWidget
     Q_OBJECT
 
 public:
-    explicit TrafficGraphWidget(QWidget *parent = 0);
+    explicit TrafficGraphWidget(QWidget *parent = nullptr);
     void setClientModel(ClientModel *model);
     int getGraphRangeMins() const;
 
diff --git a/src/qt/transactiondescdialog.h b/src/qt/transactiondescdialog.h
index f1371b3856..8fd3f3166a 100644
--- a/src/qt/transactiondescdialog.h
+++ b/src/qt/transactiondescdialog.h
@@ -21,7 +21,7 @@ class TransactionDescDialog : public QDialog
     Q_OBJECT
 
 public:
-    explicit TransactionDescDialog(const QModelIndex &idx, QWidget *parent = 0);
+    explicit TransactionDescDialog(const QModelIndex &idx, QWidget *parent = nullptr);
     ~TransactionDescDialog();
 
 private:
diff --git a/src/qt/transactionfilterproxy.h b/src/qt/transactionfilterproxy.h
index 9febd59820..685f8d3a26 100644
--- a/src/qt/transactionfilterproxy.h
+++ b/src/qt/transactionfilterproxy.h
@@ -16,7 +16,7 @@ class TransactionFilterProxy : public QSortFilterProxyModel
     Q_OBJECT
 
 public:
-    explicit TransactionFilterProxy(QObject *parent = 0);
+    explicit TransactionFilterProxy(QObject *parent = nullptr);
 
     /** Earliest date that can be represented (far in the past) */
     static const QDateTime MIN_DATE;
diff --git a/src/qt/transactiontablemodel.cpp b/src/qt/transactiontablemodel.cpp
index 01722146c5..6e4d572a9e 100644
--- a/src/qt/transactiontablemodel.cpp
+++ b/src/qt/transactiontablemodel.cpp
@@ -197,7 +197,7 @@ public:
             }
             return rec;
         }
-        return 0;
+        return nullptr;
     }
 
     QString describe(interfaces::Node& node, interfaces::Wallet& wallet, TransactionRecord *rec, int unit)
diff --git a/src/qt/transactiontablemodel.h b/src/qt/transactiontablemodel.h
index 8be3a7ab2e..7a7d98962b 100644
--- a/src/qt/transactiontablemodel.h
+++ b/src/qt/transactiontablemodel.h
@@ -28,7 +28,7 @@ class TransactionTableModel : public QAbstractTableModel
     Q_OBJECT
 
 public:
-    explicit TransactionTableModel(const PlatformStyle *platformStyle, WalletModel *parent = 0);
+    explicit TransactionTableModel(const PlatformStyle *platformStyle, WalletModel *parent = nullptr);
     ~TransactionTableModel();
 
     enum ColumnIndex {
diff --git a/src/qt/transactionview.cpp b/src/qt/transactionview.cpp
index 68410c8bd6..eb6437eb31 100644
--- a/src/qt/transactionview.cpp
+++ b/src/qt/transactionview.cpp
@@ -38,8 +38,8 @@
 #include <QVBoxLayout>
 
 TransactionView::TransactionView(const PlatformStyle *platformStyle, QWidget *parent) :
-    QWidget(parent), model(0), transactionProxyModel(0),
-    transactionView(0), abandonAction(0), bumpFeeAction(0), columnResizingFixer(0)
+    QWidget(parent), model(nullptr), transactionProxyModel(nullptr),
+    transactionView(nullptr), abandonAction(nullptr), bumpFeeAction(nullptr), columnResizingFixer(nullptr)
 {
     // Build filter row
     setContentsMargins(0,0,0,0);
diff --git a/src/qt/transactionview.h b/src/qt/transactionview.h
index fdd8b069c7..e07181d1c8 100644
--- a/src/qt/transactionview.h
+++ b/src/qt/transactionview.h
@@ -35,7 +35,7 @@ class TransactionView : public QWidget
     Q_OBJECT
 
 public:
-    explicit TransactionView(const PlatformStyle *platformStyle, QWidget *parent = 0);
+    explicit TransactionView(const PlatformStyle *platformStyle, QWidget *parent = nullptr);
 
     void setModel(WalletModel *model);
 
diff --git a/src/qt/utilitydialog.h b/src/qt/utilitydialog.h
index ad1fda4573..f1cedff282 100644
--- a/src/qt/utilitydialog.h
+++ b/src/qt/utilitydialog.h
@@ -45,7 +45,7 @@ class ShutdownWindow : public QWidget
     Q_OBJECT
 
 public:
-    explicit ShutdownWindow(QWidget *parent=0, Qt::WindowFlags f=0);
+    explicit ShutdownWindow(QWidget *parent=nullptr, Qt::WindowFlags f=Qt::Widget);
     static QWidget *showShutdownWindow(BitcoinGUI *window);
 
 protected:
diff --git a/src/qt/walletframe.h b/src/qt/walletframe.h
index 9fbc8b4d52..10d063b2b7 100644
--- a/src/qt/walletframe.h
+++ b/src/qt/walletframe.h
@@ -31,7 +31,7 @@ class WalletFrame : public QFrame
     Q_OBJECT
 
 public:
-    explicit WalletFrame(const PlatformStyle *platformStyle, BitcoinGUI *_gui = 0);
+    explicit WalletFrame(const PlatformStyle *platformStyle, BitcoinGUI *_gui = nullptr);
     ~WalletFrame();
 
     void setClientModel(ClientModel *clientModel);
diff --git a/src/qt/walletmodel.cpp b/src/qt/walletmodel.cpp
index 0a5b21f997..e1fb4819f1 100644
--- a/src/qt/walletmodel.cpp
+++ b/src/qt/walletmodel.cpp
@@ -33,9 +33,9 @@
 
 
 WalletModel::WalletModel(std::unique_ptr<interfaces::Wallet> wallet, interfaces::Node& node, const PlatformStyle *platformStyle, OptionsModel *_optionsModel, QObject *parent) :
-    QObject(parent), m_wallet(std::move(wallet)), m_node(node), optionsModel(_optionsModel), addressTableModel(0),
-    transactionTableModel(0),
-    recentRequestsTableModel(0),
+    QObject(parent), m_wallet(std::move(wallet)), m_node(node), optionsModel(_optionsModel), addressTableModel(nullptr),
+    transactionTableModel(nullptr),
+    recentRequestsTableModel(nullptr),
     cachedEncryptionStatus(Unencrypted),
     cachedNumBlocks(0)
 {
@@ -510,7 +510,7 @@ bool WalletModel::bumpFee(uint256 hash, uint256& new_hash)
     CAmount new_fee;
     CMutableTransaction mtx;
     if (!m_wallet->createBumpTransaction(hash, coin_control, 0 /* totalFee */, errors, old_fee, new_fee, mtx)) {
-        QMessageBox::critical(0, tr("Fee bump error"), tr("Increasing transaction fee failed") + "<br />(" +
+        QMessageBox::critical(nullptr, tr("Fee bump error"), tr("Increasing transaction fee failed") + "<br />(" +
             (errors.size() ? QString::fromStdString(errors[0]) : "") +")");
          return false;
     }
@@ -549,12 +549,12 @@ bool WalletModel::bumpFee(uint256 hash, uint256& new_hash)
 
     // sign bumped transaction
     if (!m_wallet->signBumpTransaction(mtx)) {
-        QMessageBox::critical(0, tr("Fee bump error"), tr("Can't sign transaction."));
+        QMessageBox::critical(nullptr, tr("Fee bump error"), tr("Can't sign transaction."));
         return false;
     }
     // commit the bumped transaction
     if(!m_wallet->commitBumpTransaction(hash, std::move(mtx), errors, new_hash)) {
-        QMessageBox::critical(0, tr("Fee bump error"), tr("Could not commit transaction") + "<br />(" +
+        QMessageBox::critical(nullptr, tr("Fee bump error"), tr("Could not commit transaction") + "<br />(" +
             QString::fromStdString(errors[0])+")");
          return false;
     }
diff --git a/src/qt/walletmodel.h b/src/qt/walletmodel.h
index 6a6c538157..c3c8f36909 100644
--- a/src/qt/walletmodel.h
+++ b/src/qt/walletmodel.h
@@ -127,7 +127,7 @@ class WalletModel : public QObject
     Q_OBJECT
 
 public:
-    explicit WalletModel(std::unique_ptr<interfaces::Wallet> wallet, interfaces::Node& node, const PlatformStyle *platformStyle, OptionsModel *optionsModel, QObject *parent = 0);
+    explicit WalletModel(std::unique_ptr<interfaces::Wallet> wallet, interfaces::Node& node, const PlatformStyle *platformStyle, OptionsModel *optionsModel, QObject *parent = nullptr);
     ~WalletModel();
 
     enum StatusCode // Returned by sendCoins
diff --git a/src/qt/walletview.cpp b/src/qt/walletview.cpp
index a619992344..dd089d8310 100644
--- a/src/qt/walletview.cpp
+++ b/src/qt/walletview.cpp
@@ -32,8 +32,8 @@
 
 WalletView::WalletView(const PlatformStyle *_platformStyle, QWidget *parent):
     QStackedWidget(parent),
-    clientModel(0),
-    walletModel(0),
+    clientModel(nullptr),
+    walletModel(nullptr),
     platformStyle(_platformStyle)
 {
     // Create tabs