Replace remaining 0 with nullptr in Qt code

Also used type-appropriate enum values such as Qt::NoItemFlags in
some cases.

All cases identified via -Wzero-as-null-pointer-constant

src/qt/addresstablemodel.cpp

@@ -300,8 +300,8 @@ QVariant AddressTableModel::headerData(int section, Qt::Orientation orientation,
 
 Qt::ItemFlags AddressTableModel::flags(const QModelIndex &index) const
 {
-    if(!index.isValid())
+    if (!index.isValid()) return Qt::NoItemFlags;
-        return 0;
+
     AddressTableEntry *rec = static_cast<AddressTableEntry*>(index.internalPointer());
 
     Qt::ItemFlags retval = Qt::ItemIsSelectable | Qt::ItemIsEnabled;

src/qt/bantablemodel.cpp

@@ -145,8 +145,7 @@ QVariant BanTableModel::headerData(int section, Qt::Orientation orientation, int
 
 Qt::ItemFlags BanTableModel::flags(const QModelIndex &index) const
 {
-    if(!index.isValid())
+    if (!index.isValid()) return Qt::NoItemFlags;
-        return 0;
 
     Qt::ItemFlags retval = Qt::ItemIsSelectable | Qt::ItemIsEnabled;
     return retval;

src/qt/bitcoin.cpp

@@ -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();
@@ -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),
+        QMessageBox::critical(nullptr, QObject::tr(PACKAGE_NAME),
-                              QObject::tr("Error: Specified data directory \"%1\" does not exist.").arg(QString::fromStdString(gArgs.GetArg("-datadir", ""))));
+            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

src/qt/bitcoinamountfield.cpp

@@ -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());

src/qt/intro.cpp

@@ -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);
 }

src/qt/networkstyle.cpp

@@ -88,5 +88,5 @@ const NetworkStyle *NetworkStyle::instantiate(const QString &networkId)
                     network_styles[x].titleAddText);
         }
     }
-    return 0;
+    return nullptr;
 }

src/qt/paymentserver.cpp

@@ -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 {

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())
+    if (!index.isValid()) return Qt::NoItemFlags;
-        return 0;
 
     Qt::ItemFlags retval = Qt::ItemIsSelectable | Qt::ItemIsEnabled;
     return retval;

src/qt/platformstyle.cpp

@@ -139,6 +139,6 @@ const PlatformStyle *PlatformStyle::instantiate(const QString &platformId)
                     platform_styles[x].useExtraSpacing);
         }
     }
-    return 0;
+    return nullptr;
 }
 

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);
 }

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();

src/qt/sendcoinsentry.cpp

@@ -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;

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;

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)

src/qt/utilitydialog.h

@@ -45,7 +45,7 @@ class ShutdownWindow : public QWidget
     Q_OBJECT
 
 public:
-    explicit ShutdownWindow(QWidget *parent=nullptr, Qt::WindowFlags f=0);
+    explicit ShutdownWindow(QWidget *parent=nullptr, Qt::WindowFlags f=Qt::Widget);
     static QWidget *showShutdownWindow(BitcoinGUI *window);
 
 protected:

src/qt/walletmodel.cpp

@@ -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;
     }

src/test/allocator_tests.cpp

@@ -105,13 +105,13 @@ BOOST_AUTO_TEST_CASE(arena_tests)
     // Go entirely wild: free and alloc interleaved,
     // generate targets and sizes using pseudo-randomness.
     for (int x=0; x<2048; ++x)
-        addr.push_back(0);
+        addr.push_back(nullptr);
     uint32_t s = 0x12345678;
     for (int x=0; x<5000; ++x) {
         int idx = s & (addr.size()-1);
         if (s & 0x80000000) {
             b.free(addr[idx]);
-            addr[idx] = 0;
+            addr[idx] = nullptr;
         } else if(!addr[idx]) {
             addr[idx] = b.alloc((s >> 16) & 2047);
         }
@@ -146,7 +146,7 @@ public:
 
             return reinterpret_cast<void*>(0x08000000 + (count<<24)); // Fake address, do not actually use this memory
         }
-        return 0;
+        return nullptr;
     }
     void FreeLocked(void* addr, size_t len) override
     {

src/wallet/db.cpp

@@ -338,7 +338,7 @@ bool BerkeleyBatch::VerifyEnvironment(const fs::path& file_path, std::string& er
     BerkeleyEnvironment* env = GetWalletEnv(file_path, walletFile);
     fs::path walletDir = env->Directory();
 
-    LogPrintf("Using BerkeleyDB version %s\n", DbEnv::version(0, 0, 0));
+    LogPrintf("Using BerkeleyDB version %s\n", DbEnv::version(nullptr, nullptr, nullptr));
     LogPrintf("Using wallet %s\n", walletFile);
 
     // Wallet file must be a plain filename without a directory