The <QtGlobal> header file includes the fundamental global declarations. It is included by most other Qt header files.

The global declarations include types , functions and macros .

The type definitions are partly convenience definitions for basic types (some of which guarantee certain bit-sizes on all platforms supported by Qt), partly types related to Qt message handling. The functions are related to generating messages, Qt version handling and comparing and adjusting object values. And finally, some of the declared macros enable programmers to add compiler or platform specific code to their applications, while others are convenience macros for larger operations.

Types

The header file declares several type definitions that guarantee a specified bit-size on all platforms supported by Qt for various basic types, for example qint8 which is a signed char guaranteed to be 8-bit on all platforms supported by Qt. The header file also declares the qlonglong type definition for long long int (__int64 on Windows).

Several convenience type definitions are declared: qreal for double or float , uchar for unsigned char, uint for unsigned int, ulong for unsigned long and ushort for unsigned short.

Finally, the QtMsgType definition identifies the various messages that can be generated and sent to a Qt message handler; QtMessageHandler is a type definition for a pointer to a function with the signature void myMessageHandler(QtMsgType, const QMessageLogContext &, const char *) . QMessageLogContext class contains the line, file, and function the message was logged at. This information is created by the QMessageLogger class.

Functions

The <QtGlobal> header file contains several functions comparing and adjusting an object’s value. These functions take a template type as argument: You can retrieve the absolute value of an object using the qAbs() function, and you can bound a given object’s value by given minimum and maximum values using the qBound() function. You can retrieve the minimum and maximum of two given objects using qMin() and qMax() respectively. All these functions return a corresponding template type; the template types can be replaced by any other type.

Example:

int myValue = 10;
int minValue = 2;
int maxValue = 6;

int boundedValue = qBound(minValue, myValue, maxValue);
// boundedValue == 6

<QtGlobal> also contains functions that generate messages from the given string argument: qDebug() , qInfo() , qWarning() , qCritical() , and qFatal() . These functions call the message handler with the given message.

Example:

if (!driver()->isOpen() || driver()->isOpenError()) {
    qWarning("QSqlQuery::exec: database not open");
    return false;
}

The remaining functions are qRound() and qRound64() , which both accept a double or float value as their argument returning the value rounded up to the nearest integer and 64-bit integer respectively, the qInstallMessageHandler() function which installs the given QtMessageHandler , and the qVersion() function which returns the version number of Qt at run-time as a string.

Macros

The <QtGlobal> header file provides a range of macros (Q_CC_*) that are defined if the application is compiled using the specified platforms. For example, the Q_CC_SUN macro is defined if the application is compiled using Forte Developer, or Sun Studio C++. The header file also declares a range of macros (Q_OS_*) that are defined for the specified platforms. For example, Q_OS_UNIX which is defined for the Unix-based systems.

The purpose of these macros is to enable programmers to add compiler or platform specific code to their application.

The remaining macros are convenience macros for larger operations: The QT_TR_NOOP() , QT_TRANSLATE_NOOP() , and QT_TRANSLATE_NOOP3() macros provide the possibility of marking strings for delayed translation. QT_TR_N_NOOP() , QT_TRANSLATE_N_NOOP() , and QT_TRANSLATE_N_NOOP3() are numerator dependent variants of these. The Q_ASSERT() and Q_ASSERT_X() enables warning messages of various level of refinement. The Q_FOREACH() and foreach() macros implement Qt’s foreach loop.

The Q_INT64_C() and Q_UINT64_C() macros wrap signed and unsigned 64-bit integer literals in a platform-independent way. The Q_CHECK_PTR() macro prints a warning containing the source code’s file name and line number, saying that the program ran out of memory, if the pointer is None . The qPrintable() and qUtf8Printable() macros represent an easy way of printing text.

The QT_POINTER_SIZE macro expands to the size of a pointer in bytes.

The macros QT_VERSION and QT_VERSION_STR expand to a numeric value or a string, respectively, that specifies the version of Qt that the application is compiled against.

See also

<QtAlgorithms> QSysInfo

Since Qt 5.13, this macro has no effect. In Qt 5.12 and before, if this macro is defined, the compiler will generate warnings if any API declared as deprecated by Qt is used.

See also

QT_DISABLE_DEPRECATED_BEFORE QT_NO_DEPRECATED_WARNINGS

This macro can be defined in the project file to disable functions deprecated in a specified version of Qt or any earlier version. The default version number is 5.0, meaning that functions deprecated in or before Qt 5.0 will not be included.

For instance, when using a future release of Qt 5, set QT_DISABLE_DEPRECATED_BEFORE=0x050100 to disable functions deprecated in Qt 5.1 and earlier. In any release, set QT_DISABLE_DEPRECATED_BEFORE=0x000000 to enable all functions, including the ones deprecated in Qt 5.0.

See also

QT_DEPRECATED_WARNINGS

This macro can be used to suppress deprecation warnings that would otherwise be generated when using deprecated APIs.

See also

QT_DISABLE_DEPRECATED_BEFORE

Expands to the size of a pointer in bytes (4 or 8). This is equivalent to sizeof(void *) but can be used in a preprocessor directive.

This macro can be used to ensure that the application is run against a recent enough version of Qt. This is especially useful if your application depends on a specific bug fix introduced in a bug-fix release (e.g., 4.0.2).

The argc and argv parameters are the main() function’s argc and argv parameters. The version parameter is a string literal that specifies which version of Qt the application requires (e.g., “4.0.2”).

Example:

#include <QApplication>
#include <QMessageBox>

int main(int argc, char *argv[])
{
    QT_REQUIRE_VERSION(argc, argv, "4.0.2")

    QApplication app(argc, argv);
    ...
    return app.exec();
}

In general, use of the Q_DECL_NOEXCEPT macro is preferred over Q_DECL_NOTHROW , because it exhibits well-defined behavior and supports the more powerful Q_DECL_NOEXCEPT_EXPR variant. However, use of Q_DECL_NOTHROW has the advantage that Windows builds benefit on a wide range or compiler versions that do not yet support the C++11 noexcept feature.

It may therefore be beneficial to use Q_DECL_NOTHROW and emulate the C++11 behavior manually with an embedded try/catch.

Qt provides the QT_TERMINATE_ON_EXCEPTION(expr) macro for this purpose. It either expands to expr (if Qt is compiled without exception support or the compiler supports C++11 noexcept semantics) or to

try { expr; } catch(...) { qTerminate(); }

otherwise.

Since this macro expands to just expr if the compiler supports C++11 noexcept, expecting the compiler to take over responsibility of calling std::terminate() in that case, it should not be used outside Q_DECL_NOTHROW functions.

See also

Q_DECL_NOEXCEPT Q_DECL_NOTHROW qTerminate()

Marks the UTF-8 encoded string literal sourceText for delayed translation in the given context . The context is typically a class name and also needs to be specified as a string literal.

The macro tells lupdate to collect the string, and expands to sourceText itself.

Example:

static const char *greeting_strings[] = {
    QT_TRANSLATE_NOOP("FriendlyConversation", "Hello"),
    QT_TRANSLATE_NOOP("FriendlyConversation", "Goodbye")
};

QString FriendlyConversation::greeting(int type)
{
    return tr(greeting_strings[type]);
}

QString global_greeting(int type)
{
    return qApp->translate("FriendlyConversation",
                           greeting_strings[type]);
}

See also

QT_TR_NOOP() QT_TRANSLATE_NOOP3() Internationalization with Qt

Marks the UTF-8 encoded string literal sourceText for delayed translation in the given context with the given disambiguation . The context is typically a class and also needs to be specified as a string literal. The string literal disambiguation should be a short semantic tag to tell apart otherwise identical strings.

The macro tells lupdate to collect the string, and expands to an anonymous struct of the two string literals passed as sourceText and disambiguation .

Example:

static { const char *source; const char *comment; } greeting_strings[] =
{
    QT_TRANSLATE_NOOP3("FriendlyConversation", "Hello",
                       "A really friendly hello"),
    QT_TRANSLATE_NOOP3("FriendlyConversation", "Goodbye",
                       "A really friendly goodbye")
};

QString FriendlyConversation::greeting(int type)
{
    return tr(greeting_strings[type].source,
              greeting_strings[type].comment);
}

QString global_greeting(int type)
{
    return qApp->translate("FriendlyConversation",
                           greeting_strings[type].source,
                           greeting_strings[type].comment);
}

See also

QT_TR_NOOP() QT_TRANSLATE_NOOP() Internationalization with Qt

Marks the UTF-8 encoded string literal sourceText for numerator dependent delayed translation in the given context . The context is typically a class name and also needs to be specified as a string literal.

The macro tells lupdate to collect the string, and expands to sourceText itself.

Example:

static const char * const greeting_strings[] = {
    QT_TRANSLATE_N_NOOP("Welcome Msg", "Hello, you have %n message(s)"),
    QT_TRANSLATE_N_NOOP("Welcome Msg", "Hi, you have %n message(s)")
};

QString global_greeting(int type, int msgcnt)
{
    return translate("Welcome Msg", greeting_strings[type], nullptr, msgcnt);
}

See also

QT_TRANSLATE_NOOP() QT_TRANSLATE_N_NOOP3() Internationalization with Qt

Marks the UTF-8 encoded string literal sourceText for numerator dependent delayed translation in the given context with the given comment . The context is typically a class and also needs to be specified as a string literal. The string literal comment should be a short semantic tag to tell apart otherwise identical strings.

The macro tells lupdate to collect the string, and expands to an anonymous struct of the two string literals passed as sourceText and comment .

Example:

static { const char * const source; const char * const comment; } status_strings[] = {
    QT_TRANSLATE_N_NOOP3("Message Status", "Hello, you have %n message(s)",
                         "A login message status"),
    QT_TRANSLATE_N_NOOP3("Message status", "You have %n new message(s)",
                         "A new message query status")
};

QString FriendlyConversation::greeting(int type, int count)
{
    return tr(status_strings[type].source,
              status_strings[type].comment, count);
}

QString global_greeting(int type, int count)
{
    return qApp->translate("Message Status",
                           status_strings[type].source,
                           status_strings[type].comment,
                           count);
}

See also

QT_TR_NOOP() QT_TRANSLATE_NOOP() QT_TRANSLATE_NOOP3() Internationalization with Qt

The macro marks an id for dynamic translation.

The only purpose of this macro is to provide an anchor for attaching meta data like to qtTrId() .

The macro expands to id .

Example:

static const char * const ids[] = {
    //% "This is the first text."
    QT_TRID_NOOP("qtn_1st_text"),
    //% "This is the second text."
    QT_TRID_NOOP("qtn_2nd_text"),
    0
};

void TheClass::addLabels()
{
    for (int i = 0; ids[i]; ++i)
        new QLabel(qtTrId(ids[i]), this);
}

See also

qtTrId() Internationalization with Qt

Marks the UTF-8 encoded string literal sourceText for delayed translation in the current context (class).

The macro tells lupdate to collect the string, and expands to sourceText itself.

Example:

QString FriendlyConversation::greeting(int type)
{
    static const char *greeting_strings[] = {
        QT_TR_NOOP("Hello"),
        QT_TR_NOOP("Goodbye")
    };
    return tr(greeting_strings[type]);
}

The macro QT_TR_NOOP_UTF8() is identical and obsolete; this applies to all other _UTF8 macros as well.

See also

QT_TRANSLATE_NOOP() Internationalization with Qt

Marks the UTF-8 encoded string literal sourceText for numerator dependent delayed translation in the current context (class).

The macro tells lupdate to collect the string, and expands to sourceText itself.

The macro expands to sourceText .

Example:

static const char * const StatusClass::status_strings[] = {
    QT_TR_N_NOOP("There are %n new message(s)"),
    QT_TR_N_NOOP("There are %n total message(s)")
};

QString StatusClass::status(int type, int count)
{
    return tr(status_strings[type], nullptr, count);
}

See also

QT_TR_NOOP Internationalization with Qt

This macro expands a numeric value of the form 0xMMNNPP (MM = major, NN = minor, PP = patch) that specifies Qt’s version number. For example, if you compile your application against Qt 4.1.2, the macro will expand to 0x040102.

You can use to use the latest Qt features where available.

Example:

#if QT_VERSION >= 0x040100
    QIcon icon = style()->standardIcon(QStyle::SP_TrashIcon);
#else
    QPixmap pixmap = style()->standardPixmap(QStyle::SP_TrashIcon);
    QIcon icon(pixmap);
#endif

See also

QT_VERSION_STR qVersion()

Turns the major, minor and patch numbers of a version into an integer, 0xMMNNPP (MM = major, NN = minor, PP = patch). This can be compared with another similarly processed version id.

Example:

#include <QtGlobal>

#if (QT_VERSION >= QT_VERSION_CHECK(5, 0, 0))
#include <QtWidgets>
#else
#include <QtGui>
#endif

See also

QT_VERSION

This macro expands to a string that specifies Qt’s version number (for example, “4.1.2”). This is the version against which the application is compiled.

See also

qVersion() QT_VERSION

Prints a warning message containing the source code file name and line number if test is false .

is useful for testing pre- and post-conditions during development. It does nothing if QT_NO_DEBUG was defined during compilation.

Example:

// File: div.cpp

#include <QtGlobal>

int divide(int a, int b)
{
    Q_ASSERT(b != 0);
    return a / b;
}

If b is zero, the statement will output the following message using the qFatal() function:

ASSERT: "b != 0" in file div.cpp, line 7

See also

Q_ASSERT_X() qFatal() Debugging Techniques

Prints the message what together with the location where , the source file name and line number if test is false .

is useful for testing pre- and post-conditions during development. It does nothing if QT_NO_DEBUG was defined during compilation.

Example:

// File: div.cpp

#include <QtGlobal>

int divide(int a, int b)
{
    Q_ASSERT_X(b != 0, "divide", "division by zero");
    return a / b;
}

If b is zero, the statement will output the following message using the qFatal() function:

ASSERT failure in divide: "division by zero", file div.cpp, line 7

See also

Q_ASSERT() qFatal() Debugging Techniques

Causes the compiler to assume that expr is true . This macro is useful for improving code generation, by providing the compiler with hints about conditions that it would not otherwise know about. However, there is no guarantee that the compiler will actually use those hints.

This macro could be considered a “lighter” version of Q_ASSERT() . While Q_ASSERT will abort the program’s execution if the condition is false , will tell the compiler not to generate code for those conditions. Therefore, it is important that the assumptions always hold, otherwise undefined behaviour may occur.

If expr is a constantly false condition, will tell the compiler that the current code execution cannot be reached. That is, (false) is equivalent to Q_UNREACHABLE() .

In debug builds the condition is enforced by an assert to facilitate debugging.

Note

Q_LIKELY() tells the compiler that the expression is likely, but not the only possibility. tells the compiler that it is the only possibility.

See also

Q_ASSERT() Q_UNREACHABLE() Q_LIKELY()

This macro represents a value you can compare to the macro Q_BYTE_ORDER to determine the endian-ness of your system. In a big-endian system, the most significant byte is stored at the lowest address. The other bytes follow in decreasing order of significance.

#if Q_BYTE_ORDER == Q_BIG_ENDIAN
...
#endif

See also

Q_BYTE_ORDER Q_LITTLE_ENDIAN

This macro can be used to determine the byte order your system uses for storing data in memory. i.e., whether your system is little-endian or big-endian. It is set by Qt to one of the macros Q_LITTLE_ENDIAN or Q_BIG_ENDIAN . You normally won’t need to worry about endian-ness, but you might, for example if you need to know which byte of an integer or UTF-16 character is stored in the lowest address. Endian-ness is important in networking, where computers with different values for must pass data back and forth.

Use this macro as in the following examples.

#if Q_BYTE_ORDER == Q_BIG_ENDIAN
...
#endif

or

#if Q_BYTE_ORDER == Q_LITTLE_ENDIAN
...
#endif

See also

Q_BIG_ENDIAN Q_LITTLE_ENDIAN

Defined if the application is compiled using Borland/Turbo C++.

Defined if the application is compiled using Reliant C++.

Defined if the application is compiled using Clang.

Defined if the application is compiled using Comeau C++.

Defined if the application is compiled using DEC C++.

Defined if the application is compiled using Edison Design Group C++.

Defined if the application is compiled using Green Hills Optimizing C++ Compilers.

Defined if the application is compiled using GNU C++.

Defined if the application is compiled using MetaWare High C/C++.

Defined if the application is compiled using HP aC++.

Defined if the application is compiled using Intel C++ for Linux, Intel C++ for Windows.

Defined if the application is compiled using KAI C++.

Defined if the application is compiled using MIPSpro C++.

Defined if the application is compiled using Microsoft Visual C/C++, Intel C++ for Windows.

Defined if the application is compiled using CenterLine C++.

Defined if the application is compiled using Portland Group C++.

Defined if the application is compiled using Forte Developer, or Sun Studio C++.

Defined if the application is compiled using Digital Mars C/C++ (used to be Symantec C++).

Defined if the application is compiled using SCO OUDK and UDK.

Defined if the application is compiled using Watcom C++.

If pointer is None , prints a message containing the source code’s file name and line number, saying that the program ran out of memory and aborts program execution. It throws std::bad_alloc instead if exceptions are enabled.

does nothing if QT_NO_DEBUG and QT_NO_EXCEPTIONS were defined during compilation. Therefore you must not use to check for successful memory allocations because the check will be disabled in some cases.

Example:

int *a;

Q_CHECK_PTR(a = new int[80]);   // WRONG!

a = new (nothrow) int[80];      // Right
Q_CHECK_PTR(a);

See also

qWarning() Debugging Techniques

You can use this macro to specify information about a custom type Type . With accurate type information, Qt’s generic containers can choose appropriate storage methods and algorithms.

Flags can be one of the following:

• Q_PRIMITIVE_TYPE specifies that Type is a POD (plain old data) type with no constructor or destructor, and for which memcpy()ing creates a valid independent copy of the object.

• Q_MOVABLE_TYPE specifies that Type has a constructor and/or a destructor but can be moved in memory using memcpy(). Note: despite the name, this has nothing to do with move constructors or C++ move semantics.

• Q_COMPLEX_TYPE (the default) specifies that Type has constructors and/or a destructor and that it may not be moved in memory.

Example of a “primitive” type:

struct Point2D
{
    int x;
    int y;
};

Q_DECLARE_TYPEINFO(Point2D, Q_PRIMITIVE_TYPE);

An example of a non-POD “primitive” type is QUuid : Even though QUuid has constructors (and therefore isn’t POD), every bit pattern still represents a valid object, and memcpy() can be used to create a valid independent copy of a QUuid object.

Example of a movable type:

class Point2D
{
public:
    Point2D() { data = new int[2]; }
    Point2D(const Point2D &other) { ... }
    ~Point2D() { delete[] data; }

    Point2D &operator=(const Point2D &other) { ... }

    int x() const { return data[0]; }
    int y() const { return data[1]; }

private:
    int *data;
};

Q_DECLARE_TYPEINFO(Point2D, Q_MOVABLE_TYPE);

Qt will try to detect the class of a type using std::is_trivial or std::is_trivially_copyable. Use this macro to tune the behavior. For instance many types would be candidates for despite not being trivially-copyable. For binary compatibility reasons, QList optimizations are only enabled if there is an explicit even for trivially-copyable types.

This macro can be used to declare variable that should be constructed at compile-time, or an inline function that can be computed at compile-time.

It expands to “constexpr” if your compiler supports that C++11 keyword, or to nothing otherwise.

See also

Q_DECL_RELAXED_CONSTEXPR

This macro marks a symbol for shared library export (see Creating Shared Libraries).

See also

Q_DECL_IMPORT

This macro can be used to declare an overriding virtual or a class as “final”, with Java semantics. Further-derived classes can then no longer override this virtual function, or inherit from this class, respectively.

It expands to “final”.

The macro goes at the end of the function, usually after the const , if any:

// more-derived classes no longer permitted to override this:
virtual void MyWidget::paintEvent(QPaintEvent*) final;

For classes, it goes in front of the : in the class definition, if any:

class QRect final { // cannot be derived from
    // ...
};

See also

Q_DECL_OVERRIDE

This macro declares a symbol to be an import from a shared library (see Creating Shared Libraries).

See also

Q_DECL_EXPORT

This macro marks a function as never throwing. If the function does nevertheless throw, the behaviour is defined: std::terminate() is called.

The macro expands to C++11 noexcept, if available, or to nothing otherwise.

If you need the operator version of C++11 noexcept, use Q_DECL_NOEXCEPT_EXPR (x).

If you don’t need C++11 noexcept semantics, e.g. because your function can’t possibly throw, don’t use this macro, use Q_DECL_NOTHROW instead.

See also

Q_DECL_NOTHROW Q_DECL_NOEXCEPT_EXPR()

This macro marks a function as non-throwing if x is true . If the function does nevertheless throw, the behaviour is defined: std::terminate() is called.

The macro expands to C++11 noexcept(x), if available, or to nothing otherwise.

If you need the always-true version of C++11 noexcept, use Q_DECL_NOEXCEPT .

If you don’t need C++11 noexcept semantics, e.g. because your function can’t possibly throw, don’t use this macro, use Q_DECL_NOTHROW instead.

See also

Q_DECL_NOTHROW Q_DECL_NOEXCEPT

This macro marks a function as never throwing, under no circumstances. If the function does nevertheless throw, the behaviour is undefined.

The macro expands to either “throw()”, if that has some benefit on the compiler, or to C++11 noexcept, if available, or to nothing otherwise.

If you need C++11 noexcept semantics, don’t use this macro, use Q_DECL_NOEXCEPT / Q_DECL_NOEXCEPT_EXPR instead.

See also

Q_DECL_NOEXCEPT Q_DECL_NOEXCEPT_EXPR()

This macro can be used to declare an overriding virtual function. Use of this markup will allow the compiler to generate an error if the overriding virtual function does not in fact override anything.

It expands to “override”.

The macro goes at the end of the function, usually after the const , if any:

// generate error if this doesn't actually override anything:
virtual void MyWidget::paintEvent(QPaintEvent*) override;

See also

Q_DECL_FINAL

This macro can be used to declare an inline function that can be computed at compile-time according to the relaxed rules from C++14.

It expands to “constexpr” if your compiler supports C++14 relaxed constant expressions, or to nothing otherwise.

See also

Q_DECL_CONSTEXPR

Can be used in switch statements at the end of case block to tell the compiler and other developers that that the lack of a break statement is intentional.

This is useful since a missing break statement is often a bug, and some compilers can be configured to emit warnings when one is not found.

See also

Q_UNREACHABLE()

Same as foreach(variable , container ).

This macro is available even when no_keywords is specified using the .pro file’s CONFIG variable.

Note

Since Qt 5.7, the use of this macro is discouraged. It will be removed in a future version of Qt. Please use C++11 range-for, possibly with qAsConst() , as needed.

See also

qAsConst()

Same as forever .

This macro is available even when no_keywords is specified using the .pro file’s CONFIG variable.

See also

foreach()

Forward-declares a Core Foundation type . This includes the actual type and the ref type. For example, (CFString) declares __CFString and CFStringRef.

Forward-declares a mutable Core Foundation type . This includes the actual type and the ref type. For example, (CFMutableString) declares __CFMutableString and CFMutableStringRef.

Forward-declares an Objective-C classname in a manner such that it can be compiled as either Objective-C or C++.

This is primarily intended for use in header files that may be included by both Objective-C and C++ source files.

Expands to a string that describe the function the macro resides in. How this string looks more specifically is compiler dependent. With GNU GCC it is typically the function signature, while with other compilers it might be the line and column number.

can be conveniently used with qDebug() . For example, this function:

template<typename TInputType>
const TInputType &myMin(const TInputType &value1, const TInputType &value2)
{
    qDebug() << Q_FUNC_INFO << "was called with value1:" << value1 << "value2:" << value2;

    if(value1 < value2)
        return value1;
    else
        return value2;
}

when instantiated with the integer type, will with the GCC compiler produce:

const TInputType& myMin(const TInputType&, const TInputType&) [with TInputType = int] was called with value1: 3 value2: 4

If this macro is used outside a function, the behavior is undefined.

Wraps the signed 64-bit integer literal in a platform-independent way.

Example:

qint64 value = Q_INT64_C(932838457459459);

See also

qint64 Q_UINT64_C()

Hints to the compiler that the enclosed condition, expr , is likely to evaluate to true .

Use of this macro can help the compiler to optimize the code.

Example:

// the condition inside the "if" will be successful most of the times
for (int i = 1; i <= 365; i++) {
    if (Q_LIKELY(isWorkingDay(i))) {
        ...
    }
    ...
}

See also

Q_UNLIKELY()

This macro represents a value you can compare to the macro Q_BYTE_ORDER to determine the endian-ness of your system. In a little-endian system, the least significant byte is stored at the lowest address. The other bytes follow in increasing order of significance.

#if Q_BYTE_ORDER == Q_LITTLE_ENDIAN
...
#endif

See also

Q_BYTE_ORDER Q_BIG_ENDIAN

Defined on AIX.

Defined on Android.

Defined on Any BSD 4.4 system.

Defined on Cygwin.

Defined on Darwin-based operating systems such as macOS, iOS, watchOS, and tvOS.

Defined on FreeBSD.

Defined on HP-UX.

Defined on GNU Hurd.

Defined on iOS.

Defined on Linux.

Defined on LynxOS.

Deprecated synonym for Q_OS_DARWIN . Do not use.

Defined on macOS.

Defined on NetBSD.

Defined on OpenBSD.

Deprecated synonym for Q_OS_MACOS . Do not use.

Defined on QNX Neutrino.

Defined on Sun Solaris.

Defined on tvOS.

Defined on Any UNIX BSD/SYSV system.

Defined on Web Assembly.

Defined on watchOS.

Defined on all supported versions of Windows. That is, if Q_OS_WIN32 , Q_OS_WIN64 , or Q_OS_WINRT is defined.

Defined on 32-bit and 64-bit versions of Windows.

Defined on 64-bit versions of Windows.

This is a synonym for Q_OS_WIN .

Defined for Windows Runtime (Windows Store apps) on Windows 8, Windows RT, and Windows Phone 8.

Defined if the application is compiled for Alpha processors.

See also

buildCpuArchitecture()

Defined if the application is compiled for ARM processors. Qt currently supports three optional ARM revisions: Q_PROCESSOR_ARM_V5 , Q_PROCESSOR_ARM_V6 , and Q_PROCESSOR_ARM_V7 .

See also

buildCpuArchitecture()

Defined if the application is compiled for ARMv5 processors. The Q_PROCESSOR_ARM macro is also defined when is defined.

See also

buildCpuArchitecture()

Defined if the application is compiled for ARMv6 processors. The Q_PROCESSOR_ARM and Q_PROCESSOR_ARM_V5 macros are also defined when is defined.

See also

buildCpuArchitecture()

Defined if the application is compiled for ARMv7 processors. The Q_PROCESSOR_ARM , Q_PROCESSOR_ARM_V5 , and Q_PROCESSOR_ARM_V6 macros are also defined when is defined.

See also

buildCpuArchitecture()

Defined if the application is compiled for AVR32 processors.

See also

buildCpuArchitecture()

Defined if the application is compiled for Blackfin processors.

See also

buildCpuArchitecture()

Defined if the application is compiled for IA-64 processors. This includes all Itanium and Itanium 2 processors.

See also

buildCpuArchitecture()

Defined if the application is compiled for MIPS processors. Qt currently supports seven MIPS revisions: Q_PROCESSOR_MIPS_I , Q_PROCESSOR_MIPS_II , Q_PROCESSOR_MIPS_III , Q_PROCESSOR_MIPS_IV , Q_PROCESSOR_MIPS_V , Q_PROCESSOR_MIPS_32 , and Q_PROCESSOR_MIPS_64 .

See also

buildCpuArchitecture()

Defined if the application is compiled for MIPS32 processors. The Q_PROCESSOR_MIPS , Q_PROCESSOR_MIPS_I , and Q_PROCESSOR_MIPS_II macros are also defined when is defined.

See also

buildCpuArchitecture()

Defined if the application is compiled for MIPS64 processors. The Q_PROCESSOR_MIPS , Q_PROCESSOR_MIPS_I , Q_PROCESSOR_MIPS_II , Q_PROCESSOR_MIPS_III , Q_PROCESSOR_MIPS_IV , and Q_PROCESSOR_MIPS_V macros are also defined when is defined.

See also

buildCpuArchitecture()

Defined if the application is compiled for MIPS-I processors. The Q_PROCESSOR_MIPS macro is also defined when is defined.

See also

buildCpuArchitecture()

Defined if the application is compiled for MIPS-II processors. The Q_PROCESSOR_MIPS and Q_PROCESSOR_MIPS_I macros are also defined when is defined.

See also

buildCpuArchitecture()

Defined if the application is compiled for MIPS-III processors. The Q_PROCESSOR_MIPS , Q_PROCESSOR_MIPS_I , and Q_PROCESSOR_MIPS_II macros are also defined when is defined.

See also

buildCpuArchitecture()

Defined if the application is compiled for MIPS-IV processors. The Q_PROCESSOR_MIPS , Q_PROCESSOR_MIPS_I , Q_PROCESSOR_MIPS_II , and Q_PROCESSOR_MIPS_III macros are also defined when is defined.

See also

buildCpuArchitecture()

Defined if the application is compiled for MIPS-V processors. The Q_PROCESSOR_MIPS , Q_PROCESSOR_MIPS_I , Q_PROCESSOR_MIPS_II , Q_PROCESSOR_MIPS_III , and Q_PROCESSOR_MIPS_IV macros are also defined when is defined.

See also

buildCpuArchitecture()

Defined if the application is compiled for POWER processors. Qt currently supports two Power variants: Q_PROCESSOR_POWER_32 and Q_PROCESSOR_POWER_64 .

See also

buildCpuArchitecture()

Defined if the application is compiled for 32-bit Power processors. The Q_PROCESSOR_POWER macro is also defined when is defined.

See also

buildCpuArchitecture()

Defined if the application is compiled for 64-bit Power processors. The Q_PROCESSOR_POWER macro is also defined when is defined.

See also

buildCpuArchitecture()

Defined if the application is compiled for RISC-V processors. Qt currently supports two RISC-V variants: Q_PROCESSOR_RISCV_32 and Q_PROCESSOR_RISCV_64 .

See also

buildCpuArchitecture()

Defined if the application is compiled for 32-bit RISC-V processors. The Q_PROCESSOR_RISCV macro is also defined when is defined.

See also

buildCpuArchitecture()

Defined if the application is compiled for 64-bit RISC-V processors. The Q_PROCESSOR_RISCV macro is also defined when is defined.

See also

buildCpuArchitecture()

Defined if the application is compiled for S/390 processors. Qt supports one optional variant of S/390: Q_PROCESSOR_S390_X .

See also

buildCpuArchitecture()

Defined if the application is compiled for S/390x processors. The Q_PROCESSOR_S390 macro is also defined when is defined.

See also

buildCpuArchitecture()

Defined if the application is compiled for SuperH processors. Qt currently supports one SuperH revision: Q_PROCESSOR_SH_4A .

See also

buildCpuArchitecture()

Defined if the application is compiled for SuperH 4A processors. The Q_PROCESSOR_SH macro is also defined when is defined.

See also

buildCpuArchitecture()

Defined if the application is compiled for SPARC processors. Qt currently supports one optional SPARC revision: Q_PROCESSOR_SPARC_V9 .

See also

buildCpuArchitecture()

Defined if the application is compiled for SPARC V9 processors. The Q_PROCESSOR_SPARC macro is also defined when is defined.

See also

buildCpuArchitecture()

Defined if the application is compiled for x86 processors. Qt currently supports two x86 variants: Q_PROCESSOR_X86_32 and Q_PROCESSOR_X86_64 .

See also

buildCpuArchitecture()

Defined if the application is compiled for 32-bit x86 processors. This includes all i386, i486, i586, and i686 processors. The Q_PROCESSOR_X86 macro is also defined when is defined.

See also

buildCpuArchitecture()

Defined if the application is compiled for 64-bit x86 processors. This includes all AMD64, Intel 64, and other x86_64/x64 processors. The Q_PROCESSOR_X86 macro is also defined when is defined.

See also

buildCpuArchitecture()

Wraps the unsigned 64-bit integer literal in a platform-independent way.

Example:

quint64 value = Q_UINT64_C(932838457459459);

See also

quint64 Q_INT64_C()

Hints to the compiler that the enclosed condition, expr , is likely to evaluate to false .

Use of this macro can help the compiler to optimize the code.

Example:

bool readConfiguration(const QFile &file)
{
    // We expect to be asked to read an existing file
    if (Q_UNLIKELY(!file.exists())) {
        qWarning() << "File not found";
        return false;
    }

    ...
    return true;
}

See also

Q_LIKELY()

Tells the compiler that the current point cannot be reached by any execution, so it may optimize any code paths leading here as dead code, as well as code continuing from here.

This macro is useful to mark impossible conditions. For example, given the following enum:

enum Shapes {
    Rectangle,
    Triangle,
    Circle,
    NumShapes
};

One can write a switch table like so:

switch (shape) {
    case Rectangle:
        return rectangle();
    case Triangle:
        return triangle();
    case Circle:
        return circle();
    case NumShapes:
        Q_UNREACHABLE();
        break;
}

The advantage of inserting at that point is that the compiler is told not to generate code for a shape variable containing that value. If the macro is missing, the compiler will still generate the necessary comparisons for that value. If the case label were removed, some compilers could produce a warning that some enum values were not checked.

By using this macro in impossible conditions, code coverage may be improved as dead code paths may be eliminated.

In debug builds the condition is enforced by an assert to facilitate debugging.

See also

Q_ASSERT() Q_ASSUME() qFatal()

Indicates to the compiler that the parameter with the specified name is not used in the body of a function. This can be used to suppress compiler warnings while allowing functions to be defined with meaningful parameter names in their signatures.

This macro is used to implement Qt’s foreach loop. The variable parameter is a variable name or variable definition; the container parameter is a Qt container whose value type corresponds to the type of the variable. See The foreach Keyword for details.

If you’re worried about namespace pollution, you can disable this macro by adding the following line to your .pro file:

CONFIG += no_keywords

Note

Since Qt 5.7, the use of this macro is discouraged. It will be removed in a future version of Qt. Please use C++11 range-for, possibly with qAsConst() , as needed.

See also

qAsConst()

This macro is provided for convenience for writing infinite loops.

Example:

forever {
    ...
}

It is equivalent to for (;;) .

If you’re worried about namespace pollution, you can disable this macro by adding the following line to your .pro file:

CONFIG += no_keywords

See also

Q_FOREVER

Compares t to the 0 of type T and returns the absolute value. Thus if T is double , then t is compared to (double) 0 .

Example:

int absoluteValue;
int myValue = -4;

absoluteValue = qAbs(myValue);
// absoluteValue == 4

Returns t cast to const T .

This function is a Qt implementation of C++17’s std::as_const(), a cast function like std::move(). But while std::move() turns lvalues into rvalues, this function turns non-const lvalues into const lvalues. Like std::as_const(), it doesn’t work on rvalues, because it cannot be efficiently implemented for rvalues without leaving dangling references.

Its main use in Qt is to prevent implicitly-shared Qt containers from detaching:

QString s = ...;
for (QChar ch : s) // detaches 's' (performs a deep-copy if 's' was shared)
    process(ch);
for (QChar ch : qAsConst(s)) // ok, no detach attempt
    process(ch);

Of course, in this case, you could (and probably should) have declared s as const in the first place:

const QString s = ...;
for (QChar ch : s) // ok, no detach attempt on const objects
    process(ch);

but often that is not easily possible.

It is important to note that does not copy its argument, it just performs a const_cast<const T&>(t) . This is also the reason why it is designed to fail for rvalues: The returned reference would go stale too soon. So while this works (but detaches the returned object):

for (QChar ch : funcReturningQString())
    process(ch); // OK, the returned object is kept alive for the loop's duration

this would not:

for (QChar ch : qAsConst(funcReturningQString()))
    process(ch); // ERROR: ch is copied from deleted memory

To prevent this construct from compiling (and failing at runtime), has a second, deleted, overload which binds to rvalues.

This is an overloaded function.

This overload is deleted to prevent a dangling reference in code like

for (QChar ch : qAsConst(funcReturningQString()))
    process(ch); // ERROR: ch is copied from deleted memory

Returns val bounded by min and max . This is equivalent to qMax (min , qMin (val , max )).

Example:

int myValue = 10;
int minValue = 2;
int maxValue = 6;

int boundedValue = qBound(minValue, myValue, maxValue);
// boundedValue == 6

See also

qMin() qMax()

Returns the memberFunctionPointer pointer to a constant member function:

struct Foo {
    void overloadedFunction(int, const QString &);
    void overloadedFunction(int, const QString &) const;
};
... qConstOverload<int, const QString &>(&Foo::overloadedFunction)
... qNonConstOverload<int, const QString &>(&Foo::overloadedFunction)

See also

qOverload qNonConstOverload Differences between String-Based and Functor-Based Connections

Calls the message handler with the critical message message . If no message handler has been installed, the message is printed to stderr. Under Windows, the message is sent to the debugger. On QNX the message is sent to slogger2.

It exits if the environment variable QT_FATAL_CRITICALS is not empty.

This function takes a format string and a list of arguments, similar to the C printf() function. The format should be a Latin-1 string.

Example:

void load(const QString &fileName)
{
    QFile file(fileName);
    if (!file.exists())
        qCritical("File '%s' does not exist!", qUtf8Printable(fileName));
}

If you include <QtDebug>, a more convenient syntax is also available:

qCritical() << "Brush:" << myQBrush << "Other
value:" << i;

A space is inserted between the items, and a newline is appended at the end.

To suppress the output at runtime, install your own message handler with qInstallMessageHandler() .

See also

qDebug() qInfo() qWarning() qFatal() qInstallMessageHandler() Debugging Techniques

Calls the message handler with the debug message message . If no message handler has been installed, the message is printed to stderr. Under Windows the message is sent to the console, if it is a console application; otherwise, it is sent to the debugger. On QNX, the message is sent to slogger2. This function does nothing if QT_NO_DEBUG_OUTPUT was defined during compilation.

If you pass the function a format string and a list of arguments, it works in similar way to the C printf() function. The format should be a Latin-1 string.

Example:

qDebug("Items in list: %d", myList.size());

If you include <QtDebug> , a more convenient syntax is also available:

qDebug() << "Brush:" << myQBrush << "Other value:" << i;

With this syntax, the function returns a QDebug object that is configured to use the QtDebugMsg message type. It automatically puts a single space between each item, and outputs a newline at the end. It supports many C++ and Qt types.

To suppress the output at run-time, install your own message handler with qInstallMessageHandler() .

See also

qInfo() qWarning() qCritical() qFatal() qInstallMessageHandler() Debugging Techniques

Returns the numerical value of the environment variable varName . If ok is not null, sets *ok to true or false depending on the success of the conversion.

Equivalent to

qgetenv(varName).toInt(ok, 0)

except that it’s much faster, and can’t throw exceptions.

Note

there’s a limit on the length of the value, which is sufficient for all valid values of int, not counting leading zeroes or spaces. Values that are too long will either be truncated or this function will set ok to false .

See also

qgetenv() qEnvironmentVariable() qEnvironmentVariableIsSet()

Returns whether the environment variable varName is empty.

Equivalent to

qgetenv(varName).isEmpty()

except that it’s potentially much faster, and can’t throw exceptions.

See also

qgetenv() qEnvironmentVariable() qEnvironmentVariableIsSet()

Returns whether the environment variable varName is set.

Equivalent to

!qgetenv(varName).isNull()

except that it’s potentially much faster, and can’t throw exceptions.

See also

qgetenv() qEnvironmentVariable() qEnvironmentVariableIsEmpty()

Replaces the value of obj with newValue and returns the old value of obj .

This is Qt’s implementation of std::exchange(). It differs from std::exchange() only in that it is constexpr already in C++14, and available on all supported compilers.

Here is how to use to implement move constructors:

MyClass(MyClass &&other)
  : m_pointer{qExchange(other.m_pointer, nullptr)},
    m_int{qExchange(other.m_int, 0)},
    m_vector{std::move(other.m_vector)},
    ...

For members of class type, we can use std::move(), as their move-constructor will do the right thing. But for scalar types such as raw pointers or integer type, move is the same as copy, which, particularly for pointers, is not what we expect. So, we cannot use std::move() for such types, but we can use std::exchange()/ to make sure the source object’s member is already reset by the time we get to the initialization of our next data member, which might come in handy if the constructor exits with an exception.

Here is how to use to write a loop that consumes the collection it iterates over:

for (auto &e : qExchange(collection, {})
    doSomethingWith(e);

Which is equivalent to the following, much more verbose code:

{
    auto tmp = std::move(collection);
    collection = {};                    // or collection.clear()
    for (auto &e : tmp)
        doSomethingWith(e);
}                                       // destroys 'tmp'

This is perfectly safe, as the for-loop keeps the result of alive for as long as the loop runs, saving the declaration of a temporary variable. Be aware, though, that returns a non-const object, so Qt containers may detach.

Calls the message handler with the fatal message message . If no message handler has been installed, the message is printed to stderr. Under Windows, the message is sent to the debugger. On QNX the message is sent to slogger2.

If you are using the default message handler this function will abort to create a core dump. On Windows, for debug builds, this function will report a _CRT_ERROR enabling you to connect a debugger to the application.

This function takes a format string and a list of arguments, similar to the C printf() function.

Example:

int divide(int a, int b)
{
    if (b == 0)                                // program error
        qFatal("divide: cannot divide by zero");
    return a / b;
}

To suppress the output at runtime, install your own message handler with qInstallMessageHandler() .

See also

qDebug() qInfo() qWarning() qCritical() qInstallMessageHandler() Debugging Techniques

Returns the number of representable floating-point numbers between a and b .

This function provides an alternative way of doing approximated comparisons of floating-point numbers similar to qFuzzyCompare() . However, it returns the distance between two numbers, which gives the caller a possibility to choose the accepted error. Errors are relative, so for instance the distance between 1.0E-5 and 1.00001E-5 will give 110, while the distance between 1.0E36 and 1.00001E36 will give 127.

This function is useful if a floating point comparison requires a certain precision. Therefore, if a and b are equal it will return 0. The maximum value it will return for 32-bit floating point numbers is 4,278,190,078. This is the distance between -FLT_MAX and +FLT_MAX .

The function does not give meaningful results if any of the arguments are Infinite or NaN . You can check for this by calling qIsFinite() .

The return value can be considered as the “error”, so if you for instance want to compare two 32-bit floating point numbers and all you need is an approximated 24-bit precision, you can use this function like this:

if (qFloatDistance(a, b) < (1 << 7)) {   // The last 7 bits are not
                                        // significant
    // precise enough
}

See also

qFuzzyCompare()

Returns the number of representable floating-point numbers between a and b .

This function serves the same purpose as qFloatDistance(float, float) , but returns the distance between two double numbers. Since the range is larger than for two float numbers ([-DBL_MAX,DBL_MAX] ), the return type is quint64.

See also

qFuzzyCompare()

Generates a formatted string out of the type , context , str arguments.

returns a QString that is formatted according to the current message pattern. It can be used by custom message handlers to format output similar to Qt’s default message handler.

The function is thread-safe.

See also

qInstallMessageHandler() qSetMessagePattern()

Classifies a floating-point value.

The return values are defined in <cmath> : returns one of the following, determined by the floating-point class of val :

• FP_NAN not a number

• FP_INFINITE infinities (positive or negative)

• FP_ZERO zero (positive or negative)

• FP_NORMAL finite with a full mantissa

• FP_SUBNORMAL finite with a reduced mantissa

This is an overloaded function.

Compares the floating point value p1 and p2 and returns true if they are considered equal, otherwise false .

Note that comparing values where either p1 or p2 is 0.0 will not work, nor does comparing values where one of the values is NaN or infinity. If one of the values is always 0.0, use qFuzzyIsNull instead. If one of the values is likely to be 0.0, one solution is to add 1.0 to both values.

// Instead of comparing with 0.0
qFuzzyCompare(0.0, 1.0e-200); // This will return false
// Compare adding 1 to both values will fix the problem
qFuzzyCompare(1 + 0.0, 1 + 1.0e-200); // This will return true

The two numbers are compared in a relative way, where the exactness is stronger the smaller the numbers are.

Compares the floating point value p1 and p2 and returns true if they are considered equal, otherwise false .

The two numbers are compared in a relative way, where the exactness is stronger the smaller the numbers are.

Compares the floating point value p1 and p2 and returns true if they are considered equal, otherwise false .

The two numbers are compared in a relative way, where the exactness is stronger the smaller the numbers are.

Returns true if the absolute value of d is within 0.000000000001 of 0.0.

Returns true if the absolute value of f is within 0.00001f of 0.0.

Returns the bit pattern for an infinite number as a double.

See also

qIsInf()

Calls the message handler with the informational message message . If no message handler has been installed, the message is printed to stderr. Under Windows, the message is sent to the console, if it is a console application; otherwise, it is sent to the debugger. On QNX the message is sent to slogger2. This function does nothing if QT_NO_INFO_OUTPUT was defined during compilation.

If you pass the function a format string and a list of arguments, it works in similar way to the C printf() function. The format should be a Latin-1 string.

Example:

qInfo("Items in list: %d", myList.size());

If you include <QtDebug> , a more convenient syntax is also available:

qInfo() << "Brush:" << myQBrush << "Other value:" << i;

With this syntax, the function returns a QDebug object that is configured to use the QtInfoMsg message type. It automatically puts a single space between each item, and outputs a newline at the end. It supports many C++ and Qt types.

To suppress the output at run-time, install your own message handler with qInstallMessageHandler() .

See also

qDebug() qWarning() qCritical() qFatal() qInstallMessageHandler() Debugging Techniques

Installs a Qt message handler which has been defined previously. Returns a pointer to the previous message handler.

The message handler is a function that prints out debug messages, warnings, critical and fatal error messages. The Qt library (debug mode) contains hundreds of warning messages that are printed when internal errors (usually invalid function arguments) occur. Qt built in release mode also contains such warnings unless QT_NO_WARNING_OUTPUT and/or QT_NO_DEBUG_OUTPUT have been set during compilation. If you implement your own message handler, you get total control of these messages.

The default message handler prints the message to the standard output under X11 or to the debugger under Windows. If it is a fatal message, the application aborts immediately.

Only one message handler can be defined, since this is usually done on an application-wide basis to control debug output.

To restore the message handler, call qInstallMessageHandler(0) .

Example:

#include <qapplication.h>
#include <stdio.h>
#include <stdlib.h>

void myMessageOutput(QtMsgType type, const QMessageLogContext &context, const QString &msg)
{
    QByteArray localMsg = msg.toLocal8Bit();
    const char *file = context.file ? context.file : "";
    const char *function = context.function ? context.function : "";
    switch (type) {
    case QtDebugMsg:
        fprintf(stderr, "Debug: %s (%s:%u, %s)\n", localMsg.constData(), file, context.line, function);
        break;
    case QtInfoMsg:
        fprintf(stderr, "Info: %s (%s:%u, %s)\n", localMsg.constData(), file, context.line, function);
        break;
    case QtWarningMsg:
        fprintf(stderr, "Warning: %s (%s:%u, %s)\n", localMsg.constData(), file, context.line, function);
        break;
    case QtCriticalMsg:
        fprintf(stderr, "Critical: %s (%s:%u, %s)\n", localMsg.constData(), file, context.line, function);
        break;
    case QtFatalMsg:
        fprintf(stderr, "Fatal: %s (%s:%u, %s)\n", localMsg.constData(), file, context.line, function);
        break;
    }
}

int main(int argc, char **argv)
{
    qInstallMessageHandler(myMessageOutput);
    QApplication app(argc, argv);
    ...
    return app.exec();
}

See also

QtMessageHandler QtMsgType qDebug() qInfo() qWarning() qCritical() qFatal() Debugging Techniques

Installs a Qt message handler which has been defined previously. This method is deprecated, use qInstallMessageHandler instead.

See also

QtMsgHandler qInstallMessageHandler()

Returns true if the double d is a finite number.

Returns true if the float f is a finite number.

Returns true if the qfloat16 f is a finite number.

See also

qIsFinite

Returns true if the double d is equivalent to infinity.

See also

qInf()

Returns true if the float f is equivalent to infinity.

See also

qInf()

Returns true if the qfloat16 f is equivalent to infinity.

See also

qIsInf

Returns true if the double d is not a number (NaN).

Returns true if the float f is not a number (NaN).

Returns true if the qfloat16 f is not a number (NaN).

See also

qIsNaN

Returns the maximum of a and b .

Example:

int myValue = 6;
int yourValue = 4;

int maxValue = qMax(myValue, yourValue);
// maxValue == myValue

See also

qMin() qBound()

Returns the minimum of a and b .

Example:

int myValue = 6;
int yourValue = 4;

int minValue = qMin(myValue, yourValue);
// minValue == yourValue

See also

qMax() qBound()

Use std::move instead.

It expands to “std::move”.

takes an rvalue reference to its parameter x , and converts it to an xvalue.

Returns the memberFunctionPointer pointer to a non-constant member function:

struct Foo {
    void overloadedFunction(int, const QString &);
    void overloadedFunction(int, const QString &) const;
};
... qConstOverload<int, const QString &>(&Foo::overloadedFunction)
... qNonConstOverload<int, const QString &>(&Foo::overloadedFunction)

See also

qOverload qNonConstOverloadDifferences between String-Based and Functor-Based Connections

Returns a pointer to an overloaded function. The template parameter is the list of the argument types of the function. functionPointer is the pointer to the (member) function:

struct Foo {
    void overloadedFunction();
    void overloadedFunction(int, const QString &);
};
... qOverload<>(&Foo::overloadedFunction)
... qOverload<int, const QString &>(&Foo::overloadedFunction)

If a member function is also const-overloaded qConstOverload and qNonConstOverload need to be used.

requires C++14 enabled. In C++11-only code, the helper classes QOverload, QConstOverload, and QNonConstOverload can be used directly:

... QOverload<>::of(&Foo::overloadedFunction)
... QOverload<int, const QString &>::of(&Foo::overloadedFunction)

Note

Qt detects the necessary C++14 compiler support by way of the feature test recommendations from C++ Committee’s Standing Document 6 .

See also

qConstOverload() qNonConstOverload() Differences between String-Based and Functor-Based Connections

Returns str as a const char * . This is equivalent to str .toLocal8Bit().constData().

The char pointer will be invalid after the statement in which is used. This is because the array returned by toLocal8Bit() will fall out of scope.

Note

qDebug() , qInfo() , qWarning() , qCritical() , qFatal() expect %s arguments to be UTF-8 encoded, while converts to local 8-bit encoding. Therefore qUtf8Printable() should be used for logging strings instead of .

See also

qUtf8Printable()

Returns the bit pattern of a quiet NaN as a double.

See also

qIsNaN()

Rounds d to the nearest integer.

Rounds half up (e.g. 0.5 -> 1, -0.5 -> 0).

Example:

double valueA = 2.3;
double valueB = 2.7;

int roundedValueA = qRound(valueA);
// roundedValueA = 2
int roundedValueB = qRound(valueB);
// roundedValueB = 3

Rounds d to the nearest integer.

Rounds half up (e.g. 0.5f -> 1, -0.5f -> 0).

Example:

float valueA = 2.3;
float valueB = 2.7;

int roundedValueA = qRound(valueA);
// roundedValueA = 2
int roundedValueB = qRound(valueB);
// roundedValueB = 3

Rounds value to the nearest integer.

See also

qRound

Rounds d to the nearest 64-bit integer.

Rounds half up (e.g. 0.5 -> 1, -0.5 -> 0).

Example:

double valueA = 42949672960.3;
double valueB = 42949672960.7;

qint64 roundedValueA = qRound64(valueA);
// roundedValueA = 42949672960
qint64 roundedValueB = qRound64(valueB);
// roundedValueB = 42949672961

Rounds d to the nearest 64-bit integer.

Rounds half up (e.g. 0.5f -> 1, -0.5f -> 0).

Example:

float valueA = 42949672960.3;
float valueB = 42949672960.7;

qint64 roundedValueA = qRound64(valueA);
// roundedValueA = 42949672960
qint64 roundedValueB = qRound64(valueB);
// roundedValueB = 42949672961

Rounds value to the nearest 64-bit integer.

See also

qRound64

Returns the bit pattern of a signalling NaN as a double.

Changes the output of the default message handler.

Allows to tweak the output of qDebug() , qInfo() , qWarning() , qCritical() , and qFatal() . The category logging output of qCDebug() , qCInfo() , qCWarning() , and qCCritical() is formatted, too.

Following placeholders are supported:

Placeholder	Description
%{appname}	applicationName()
%{category}	Logging category
%{file}	Path to source file
%{function}	Function
%{line}	Line in source file
%{message}	The actual message
%{pid}	applicationPid()
%{threadid}	The system-wide ID of current thread (if it can be obtained)
%{qthreadptr}	A pointer to the current QThread (result of currentThread() )
%{type}	“debug”, “warning”, “critical” or “fatal”
%{time process}	time of the message, in seconds since the process started (the token “process” is literal)
%{time boot}	the time of the message, in seconds since the system boot if that can be determined (the token “boot” is literal). If the time since boot could not be obtained, the output is indeterminate (see msecsSinceReference() ).
%{time [format]}	system time when the message occurred, formatted by passing the format to toString() . If the format is not specified, the format of ISODate is used.
%{backtrace [depth=N] [separator="..."]}	A backtrace with the number of frames specified by the optional depth parameter (defaults to 5), and separated by the optional separator parameter (defaults to “|”). This expansion is available only on some platforms (currently only platfoms using glibc). Names are only known for exported functions. If you want to see the name of every function in your application, use QMAKE_LFLAGS += -rdynamic . When reading backtraces, take into account that frames might be missing due to inlining or tail call optimization.

You can also use conditionals on the type of the message using %{if-debug} , %{if-info} %{if-warning} , %{if-critical} or %{if-fatal} followed by an %{endif} . What is inside the %{if-*} and %{endif} will only be printed if the type matches.

Finally, text inside %{if-category} … %{endif} is only printed if the category is not the default one.

Example:

QT_MESSAGE_PATTERN="[%{time yyyyMMdd h:mm:ss.zzz t} %{if-debug}D%{endif}%{if-info}I%{endif}%{if-warning}W%{endif}%{if-critical}C%{endif}%{if-fatal}F%{endif}] %{file}:%{line} - %{message}"

The default pattern is “%{if-category}%{category}: %{endif}%{message}”.

The pattern can also be changed at runtime by setting the QT_MESSAGE_PATTERN environment variable; if both qSetMessagePattern() is called and QT_MESSAGE_PATTERN is set, the environment variable takes precedence.

Note

The message pattern only applies to unstructured logging, such as the default stderr output. Structured logging such as systemd will record the message as is, along with as much structured information as can be captured.

Custom message handlers can use qFormatLogMessage() to take pattern into account.

See also

qInstallMessageHandler() QLoggingCategory

Returns str as a const ushort * , but cast to a const wchar_t * to avoid warnings. This is equivalent to str .utf16() plus some casting.

The only useful thing you can do with the return value of this macro is to pass it to asprintf() for use in a %ls conversion. In particular, the return value is not a valid const wchar_t* !

In general, the pointer will be invalid after the statement in which is used. This is because the pointer may have been obtained from a temporary expression, which will fall out of scope.

Example:

qWarning("%ls: %ls", qUtf16Printable(key), qUtf16Printable(value));

See also

qPrintable() qDebug() qInfo() qWarning() qCritical() qFatal()

Returns str as a const char * . This is equivalent to str .toUtf8().constData().

The char pointer will be invalid after the statement in which is used. This is because the array returned by toUtf8() will fall out of scope.

Example:

qWarning("%s: %s", qUtf8Printable(key), qUtf8Printable(value));

See also

qPrintable() qDebug() qInfo() qWarning() qCritical() qFatal()

Returns the version number of Qt at run-time as a string (for example, “4.1.2”). This may be a different version than the version the application was compiled against.

See also

QT_VERSION_STR version()

Calls the message handler with the warning message message . If no message handler has been installed, the message is printed to stderr. Under Windows, the message is sent to the debugger. On QNX the message is sent to slogger2. This function does nothing if QT_NO_WARNING_OUTPUT was defined during compilation; it exits if at the nth warning corresponding to the counter in environment variable QT_FATAL_WARNINGS . That is, if the environment variable contains the value 1, it will exit on the 1st message; if it contains the value 10, it will exit on the 10th message. Any non-numeric value is equivalent to 1.

This function takes a format string and a list of arguments, similar to the C printf() function. The format should be a Latin-1 string.

Example:

void f(int c)
{
    if (c > 200)
        qWarning("f: bad argument, c == %d", c);
}

If you include <QtDebug>, a more convenient syntax is also available:

qWarning() << "Brush:" << myQBrush << "Other value:"
<< i;

This syntax inserts a space between each item, and appends a newline at the end.

To suppress the output at runtime, install your own message handler with qInstallMessageHandler() .

See also

qDebug() qInfo() qCritical() qFatal() qInstallMessageHandler() Debugging Techniques

Uses Q_CHECK_PTR on p , then returns p .

This can be used as an inline version of Q_CHECK_PTR .

Returns the value of the environment variable with name varName as a QByteArray . If no variable by that name is found in the environment, this function returns a default-constructed QByteArray .

The Qt environment manipulation functions are thread-safe, but this requires that the C library equivalent functions like getenv and putenv are not directly called.

To convert the data to a QString use fromLocal8Bit() .

Note

on desktop Windows, may produce data loss if the original string contains Unicode characters not representable in the ANSI encoding. Use qEnvironmentVariable() instead. On Unix systems, this function is lossless.

See also

qputenv() qEnvironmentVariable() qEnvironmentVariableIsSet() qEnvironmentVariableIsEmpty()

This function sets the value of the environment variable named varName . It will create the variable if it does not exist. It returns 0 if the variable could not be set.

Calling qputenv with an empty value removes the environment variable on Windows, and makes it set (but empty) on Unix. Prefer using qunsetenv() for fully portable behavior.

Note

was introduced because putenv() from the standard C library was deprecated in VC2005 (and later versions). uses the replacement function in VC, and calls the standard C library’s implementation on all other platforms.

See also

qgetenv() qEnvironmentVariable()

Thread-safe version of the standard C++ rand() function.

Returns a value between 0 and RAND_MAX (defined in <cstdlib> and <stdlib.h> ), the next number in the current sequence of pseudo-random integers.

Use qsrand() to initialize the pseudo-random number generator with a seed value. Seeding must be performed at least once on each thread. If that step is skipped, then the sequence will be pre-seeded with a constant value.

Note

This function is deprecated. In new applications, use QRandomGenerator instead.

See also

qsrand() QRandomGenerator

Thread-safe version of the standard C++ srand() function.

Sets the argument seed to be used to generate a new random number sequence of pseudo random integers to be returned by qrand() .

The sequence of random numbers generated is deterministic per thread. For example, if two threads call qsrand(1) and subsequently call qrand() , the threads will get the same random number sequence.

Note

This function is deprecated. In new applications, use QRandomGenerator instead.

See also

qrand() QRandomGenerator

The function finds and returns a translated string.

Returns a translated string identified by id . If no matching string is found, the id itself is returned. This should not happen under normal conditions.

If n >= 0, all occurrences of %n in the resulting string are replaced with a decimal representation of n . In addition, depending on n ‘s value, the translation text may vary.

Meta data and comments can be passed as documented for tr() . In addition, it is possible to supply a source string template like that:

//% <C string>

or

\begincomment% <C string> \endcomment

Example:

//% "%n fooish bar(s) found.\n"
//% "Do you want to continue?"
QString text = qtTrId("qtn_foo_bar", n);

Creating QM files suitable for use with this function requires passing the -idbased option to the lrelease tool.

Warning

This method is reentrant only if all translators are installed before calling this method. Installing or removing translators while performing translations is not supported. Doing so will probably result in crashes or other undesirable behavior.

See also

tr() translate() Internationalization with Qt

This function deletes the variable varName from the environment.

Returns true on success.

See also

qputenv() qgetenv() qEnvironmentVariable()

This enum describes the messages that can be sent to a message handler ( QtMessageHandler ). You can use the enum to identify and associate the various message types with the appropriate actions.

Constant	Description
QtDebugMsg	A message generated by the qDebug() function.
QtInfoMsg	A message generated by the qInfo() function.
QtWarningMsg	A message generated by the qWarning() function.
QtCriticalMsg	A message generated by the qCritical() function.
QtFatalMsg	A message generated by the qFatal() function.
QtSystemMsg

QtInfoMsg was added in Qt 5.5.

See also

QtMessageHandler qInstallMessageHandler()

This is a typedef for void (*)() , a pointer to a function that takes no arguments and returns void.

This is a typedef for a pointer to a function with the following signature:

void myMessageHandler(QtMsgType, const QMessageLogContext &, const QString &);

See also

QtMsgType qInstallMessageHandler()

This is a typedef for a pointer to a function with the following signature:

void myMsgHandler(QtMsgType, const char *);

This typedef is deprecated, you should use QtMessageHandler instead.

See also

QtMsgType QtMessageHandler qInstallMsgHandler() qInstallMessageHandler()

Typedef for signed short . This type is guaranteed to be 16-bit on all platforms supported by Qt.

Typedef for signed int . This type is guaranteed to be 32-bit on all platforms supported by Qt.

Typedef for long long int (__int64 on Windows). This type is guaranteed to be 64-bit on all platforms supported by Qt.

Literals of this type can be created using the Q_INT64_C() macro:

qint64 value = Q_INT64_C(932838457459459);

See also

Q_INT64_C() quint64 qlonglong

Typedef for signed char . This type is guaranteed to be 8-bit on all platforms supported by Qt.

Integral type for representing pointers in a signed integer (useful for hashing, etc.).

Typedef for either qint32 or qint64. This type is guaranteed to be the same size as a pointer on all platforms supported by Qt. On a system with 32-bit pointers, qintptr is a typedef for qint32; on a system with 64-bit pointers, qintptr is a typedef for qint64.

Note that qintptr is signed. Use quintptr for unsigned values.

See also

qptrdiff qint32 qint64

Typedef for long long int (__int64 on Windows). This is the same as qint64 .

See also

qulonglong qint64

Integral type for representing pointer differences.

Typedef for either qint32 or qint64. This type is guaranteed to be the same size as a pointer on all platforms supported by Qt. On a system with 32-bit pointers, quintptr is a typedef for quint32; on a system with 64-bit pointers, quintptr is a typedef for quint64.

Note that qptrdiff is signed. Use quintptr for unsigned values.

See also

quintptr qint32 qint64

Typedef for double unless Qt is configured with the -qreal float option.

Typedef for unsigned short . This type is guaranteed to be 16-bit on all platforms supported by Qt.

Typedef for unsigned int . This type is guaranteed to be 32-bit on all platforms supported by Qt.

Typedef for unsigned long long int (unsigned __int64 on Windows). This type is guaranteed to be 64-bit on all platforms supported by Qt.

Literals of this type can be created using the Q_UINT64_C() macro:

quint64 value = Q_UINT64_C(932838457459459);

See also

Q_UINT64_C() qint64 qulonglong

Typedef for unsigned char . This type is guaranteed to be 8-bit on all platforms supported by Qt.

Integral type for representing pointers in an unsigned integer (useful for hashing, etc.).

Typedef for either quint32 or quint64. This type is guaranteed to be the same size as a pointer on all platforms supported by Qt. On a system with 32-bit pointers, quintptr is a typedef for quint32; on a system with 64-bit pointers, quintptr is a typedef for quint64.

Note that quintptr is unsigned. Use qptrdiff for signed values.

See also

qptrdiff quint32 quint64

Typedef for unsigned long long int (unsigned __int64 on Windows). This is the same as quint64 .

See also

quint64 qlonglong

Convenience typedef for unsigned char .

Convenience typedef for unsigned int .

Convenience typedef for unsigned long .

Convenience typedef for unsigned short .

Integral type providing Posix’ ssize_t for all platforms.

This type is guaranteed to be the same size as a size_t on all platforms supported by Qt.

Note that qsizetype is signed. Use size_t for unsigned values.

See also

qptrdiff