The <QtGlobal> header file includes the fundamental global declarations. It is included by most other Qt header files. More...
Header: | #include <QtGlobal> |
QFunctionPointer | |
QtMessageHandler | |
enum | QtMsgType { QtDebugMsg, QtInfoMsg, QtWarningMsg, QtCriticalMsg, QtFatalMsg, QtSystemMsg } |
qint8 | |
qint16 | |
qint32 | |
qint64 | |
qintptr | |
qlonglong | |
qptrdiff | |
qreal | |
qsizetype | |
quint8 | |
quint16 | |
quint32 | |
quint64 | |
quintptr | |
qulonglong | |
uchar | |
uint | |
ulong | |
ushort |
T | qAbs(const T &t) |
typename std::add_const<T>::type & | qAsConst(T &t) |
void | qAsConst(const T &&t) |
const T & | qBound(const T &min, const T &val, const T &max) |
auto | qConstOverload(T memberFunctionPointer) |
QString | qEnvironmentVariable(const char *varName, const QString &defaultValue) |
QString | qEnvironmentVariable(const char *varName) |
int | qEnvironmentVariableIntValue(const char *varName, bool *ok = nullptr) |
bool | qEnvironmentVariableIsEmpty(const char *varName) |
bool | qEnvironmentVariableIsSet(const char *varName) |
T | qExchange(T &obj, U &&newValue) |
quint32 | qFloatDistance(float a, float b) |
quint64 | qFloatDistance(double a, double b) |
QString | qFormatLogMessage(QtMsgType type, const QMessageLogContext &context, const QString &str) |
int | qFpClassify(double val) |
int | qFpClassify(float val) |
bool | qFuzzyCompare(double p1, double p2) |
bool | qFuzzyCompare(float p1, float p2) |
bool | qFuzzyIsNull(double d) |
bool | qFuzzyIsNull(float f) |
double | qInf() |
QtMessageHandler | qInstallMessageHandler(QtMessageHandler handler) |
bool | qIsFinite(double d) |
bool | qIsFinite(float f) |
bool | qIsInf(double d) |
bool | qIsInf(float f) |
bool | qIsNaN(double d) |
bool | qIsNaN(float f) |
const T & | qMax(const T &a, const T &b) |
const T & | qMin(const T &a, const T &b) |
auto | qNonConstOverload(T memberFunctionPointer) |
auto | qOverload(T functionPointer) |
double | qQNaN() |
qint64 | qRound64(double d) |
qint64 | qRound64(float d) |
int | qRound(double d) |
int | qRound(float d) |
double | qSNaN() |
void | qSetMessagePattern(const QString &pattern) |
std::underlying_type_t<Enum> | qToUnderlying(Enum e) |
const char * | qVersion() |
T * | q_check_ptr(T *p) |
QByteArray | qgetenv(const char *varName) |
bool | qputenv(const char *varName, const QByteArray &value) |
QString | qtTrId(const char *id, int n = -1) |
bool | qunsetenv(const char *varName) |
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.
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.
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.
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 nullptr
. 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> and QSysInfo.
This is a typedef for void (*)()
, a pointer to a function that takes no arguments and returns void.
[since 5.0]
QtMessageHandler
This is a typedef for a pointer to a function with the following signature:
void myMessageHandler(QtMsgType, const QMessageLogContext &, const QString &);
This typedef was introduced in Qt 5.0.
See also QtMsgType and qInstallMessageHandler().
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 | Value | Description |
---|---|---|
QtDebugMsg |
0 |
A message generated by the qDebug() function. |
QtInfoMsg |
4 |
A message generated by the qInfo() function. |
QtWarningMsg |
1 |
A message generated by the qWarning() function. |
QtCriticalMsg |
2 |
A message generated by the qCritical() function. |
QtFatalMsg |
3 |
A message generated by the qFatal() function. |
QtSystemMsg |
QtCriticalMsg |
QtInfoMsg
was added in Qt 5.5.
See also QtMessageHandler and qInstallMessageHandler().
Typedef for signed char
. This type is guaranteed to be 8-bit on all platforms supported by Qt.
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
. 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, and qlonglong.
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.
In order to print values of this type by using formatted-output facilities such as printf()
, qDebug(), QString::asprintf() and so on, you can use the PRIdQINTPTR
and PRIiQINTPTR
macros as format specifiers. They will both print the value as a base 10 number.
qintptr p = 123; printf("The pointer is %" PRIdQINTPTR "\n", p);
See also qptrdiff, qint32, and qint64.
Typedef for long long int
(__int64
on Windows). This is the same as qint64.
See also qulonglong and 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.
In order to print values of this type by using formatted-output facilities such as printf()
, qDebug(), QString::asprintf() and so on, you can use the PRIdQPTRDIFF
and PRIiQPTRDIFF
macros as format specifiers. They will both print the value as a base 10 number.
qptrdiff d = 123; printf("The difference is %" PRIdQPTRDIFF "\n", d);
See also quintptr, qint32, and qint64.
Typedef for double
unless Qt is configured with the -qreal float
option.
[alias, since 5.10]
qsizetype
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.
In order to print values of this type by using formatted-output facilities such as printf()
, qDebug(), QString::asprintf() and so on, you can use the PRIdQSIZETYPE
and PRIiQSIZETYPE
macros as format specifiers. They will both print the value as a base 10 number.
qsizetype s = 123; printf("The size is %" PRIdQSIZETYPE "\n", s);
This typedef was introduced in Qt 5.10.
See also qptrdiff.
Typedef for unsigned char
. This type is guaranteed to be 8-bit on all platforms supported by Qt.
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
. 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, and qulonglong.
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.
In order to print values of this type by using formatted-output facilities such as printf()
, qDebug(), QString::asprintf() and so on, you can use the following macros as format specifiers:
PRIuQUINTPTR
: prints the value as a base 10 number.PRIoQUINTPTR
: prints the value as a base 8 number.PRIxQUINTPTR
: prints the value as a base 16 number, using lowercase a-f
letters.PRIXQUINTPTR
: prints the value as a base 16 number, using uppercase A-F
letters.quintptr p = 123u; printf("The pointer value is 0x%" PRIXQUINTPTR "\n", p);
See also qptrdiff, quint32, and quint64.
Typedef for unsigned long long int
(unsigned __int64
on Windows). This is the same as quint64.
See also quint64 and qlonglong.
Convenience typedef for unsigned char
.
Convenience typedef for unsigned int
.
Convenience typedef for unsigned long
.
Convenience typedef for unsigned short
.
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:
[since 5.10]
QString qEnvironmentVariable(const char *varName)
[since 5.10]
QString qEnvironmentVariable(const char *varName, const QString &defaultValue)
These functions return the value of the environment variable, varName, as a QString. If no variable varName is found in the environment and defaultValue is provided, defaultValue is returned. Otherwise QString() is returned.
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.
The following table describes how to choose between qgetenv() and qEnvironmentVariable():
Condition | Recommendation |
---|---|
Variable contains file paths or user text | qEnvironmentVariable() |
Windows-specific code | qEnvironmentVariable() |
Unix-specific code, destination variable is not QString and/or is used to interface with non-Qt APIs | qgetenv() |
Destination variable is a QString | qEnvironmentVariable() |
Destination variable is a QByteArray or std::string | qgetenv() |
Note: on Unix systems, this function may produce data loss if the original string contains arbitrary binary data that cannot be decoded by the locale codec. Use qgetenv() instead for that case. On Windows, this function is lossless.
Note: the variable name varName must contain only US-ASCII characters.
This function was introduced in Qt 5.10.
See also qputenv(), qgetenv(), qEnvironmentVariableIsSet(), and qEnvironmentVariableIsEmpty().
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
[since 5.7]
template <typename T> typename std::add_const<T>::type &qAsConst(T &t)
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 qAsConst() 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), qAsConst() has a second, deleted, overload which binds to rvalues.
This function was introduced in Qt 5.7.
[since 5.7]
template <typename T> void qAsConst(const T &&t)
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
This function was introduced in Qt 5.7.
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
[since 5.7]
template <typename T> auto qConstOverload(T memberFunctionPointer)
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)
This function was introduced in Qt 5.7.
See also qOverload, qNonConstOverload, and Differences between String-Based and Functor-Based Connections.
[since 5.10]
QString qEnvironmentVariable(const char *varName, const QString &defaultValue)
This function was introduced in Qt 5.10.
[since 5.10]
QString qEnvironmentVariable(const char *varName)
This function was introduced in Qt 5.10.
[since 5.5]
int qEnvironmentVariableIntValue(const char *varName, bool *ok = nullptr)
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
.
This function was introduced in Qt 5.5.
See also qgetenv(), qEnvironmentVariable(), and qEnvironmentVariableIsSet().
[since 5.1]
bool qEnvironmentVariableIsEmpty(const char *varName)
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.
This function was introduced in Qt 5.1.
See also qgetenv(), qEnvironmentVariable(), and qEnvironmentVariableIsSet().
[since 5.1]
bool qEnvironmentVariableIsSet(const char *varName)
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.
This function was introduced in Qt 5.1.
See also qgetenv(), qEnvironmentVariable(), and qEnvironmentVariableIsEmpty().
[since 5.14]
template <typename T, typename U> T qExchange(T &obj, U &&newValue)
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 qExchange() 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()/qExchange() 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 qExchange() 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 qExchange() alive for as long as the loop runs, saving the declaration of a temporary variable. Be aware, though, that qExchange() returns a non-const object, so Qt containers may detach.
This function was introduced in Qt 5.14.
[since 5.2]
quint32 qFloatDistance(float a, float b)
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 }
This function was introduced in Qt 5.2.
See also qFuzzyCompare().
[since 5.2]
quint64 qFloatDistance(double a, double b)
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.
This function was introduced in Qt 5.2.
See also qFuzzyCompare().
[since 5.4]
QString qFormatLogMessage(QtMsgType type, const QMessageLogContext &context, const QString &str)
Generates a formatted string out of the type, context, str arguments.
qFormatLogMessage 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.
This function was introduced in Qt 5.4.
See also qInstallMessageHandler() and qSetMessagePattern().
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.
Note: This function is thread-safe.
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.
Note: This function is thread-safe.
Returns true if the absolute value of d is within 0.000000000001 of 0.0.
Note: This function is thread-safe.
Returns true if the absolute value of f is within 0.00001f of 0.0.
Note: This function is thread-safe.
Returns the bit pattern for an infinite number as a double.
See also qIsInf().
[since 5.0]
QtMessageHandler qInstallMessageHandler(QtMessageHandler handler)
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(); }
This function was introduced in Qt 5.0.
See also QtMessageHandler, QtMsgType, qDebug(), qInfo(), qWarning(), qCritical(), qFatal(), and Debugging Techniques.
Returns true
if the double d is a finite number.
Returns true
if the float f is a finite number.
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 double d is not a number (NaN).
Returns true
if the float f is not a number (NaN).
Returns the maximum of a and b.
Example:
int myValue = 6; int yourValue = 4; int maxValue = qMax(myValue, yourValue); // maxValue == myValue
Returns the minimum of a and b.
Example:
int myValue = 6; int yourValue = 4; int minValue = qMin(myValue, yourValue); // minValue == yourValue
[since 5.7]
template <typename T> auto qNonConstOverload(T memberFunctionPointer)
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)
This function was introduced in Qt 5.7.
See also qOverload, qNonConstOverload, and Differences between String-Based and Functor-Based Connections.
[since 5.7]
template <typename T> auto qOverload(T functionPointer)
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.
qOverload() 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.
This function was introduced in Qt 5.7.
See also qConstOverload(), qNonConstOverload(), and Differences between String-Based and Functor-Based Connections.
Returns the bit pattern of a quiet NaN as a double.
See also qIsNaN().
Rounds d to the nearest 64-bit integer.
Rounds half away from zero (e.g. 0.5 -> 1, -0.5 -> -1).
Note: This function does not guarantee correctness for high precisions.
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 away from zero (e.g. 0.5f -> 1, -0.5f -> -1).
Note: This function does not guarantee correctness for high precisions.
Example:
float valueA = 42949672960.3; float valueB = 42949672960.7; qint64 roundedValueA = qRound64(valueA); // roundedValueA = 42949672960 qint64 roundedValueB = qRound64(valueB); // roundedValueB = 42949672961
Rounds d to the nearest integer.
Rounds half away from zero (e.g. 0.5 -> 1, -0.5 -> -1).
Note: This function does not guarantee correctness for high precisions.
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 away from zero (e.g. 0.5f -> 1, -0.5f -> -1).
Note: This function does not guarantee correctness for high precisions.
Example:
float valueA = 2.3; float valueB = 2.7; int roundedValueA = qRound(valueA); // roundedValueA = 2 int roundedValueB = qRound(valueB); // roundedValueB = 3
Returns the bit pattern of a signalling NaN as a double.
[since 5.0]
void qSetMessagePattern(const QString &pattern)
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} |
QCoreApplication::applicationName() |
%{category} |
Logging category |
%{file} |
Path to source file |
%{function} |
Function |
%{line} |
Line in source file |
%{message} |
The actual message |
%{pid} |
QCoreApplication::applicationPid() |
%{threadid} |
The system-wide ID of current thread (if it can be obtained) |
%{qthreadptr} |
A pointer to the current QThread (result of QThread::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 QElapsedTimer::msecsSinceReference()). |
%{time [format]} |
system time when the message occurred, formatted by passing the format to QDateTime::toString(). If the format is not specified, the format of Qt::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 information for the placeholders category
, file
, function
and line
is only recorded in debug builds. Alternatively, QT_MESSAGELOGCONTEXT
can be defined explicitly. For more information refer to the QMessageLogContext documentation.
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.
This function was introduced in Qt 5.0.
See also qInstallMessageHandler(), Debugging Techniques, QLoggingCategory, and QMessageLogContext.
[since 6.2]
template <typename Enum> std::underlying_type_t<Enum> qToUnderlying(Enum e)
Converts the enumerator e to the equivalent value expressed in its enumeration's underlying type.
This function was introduced in Qt 6.2.
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 and QLibraryInfo::version().
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 QString::fromLocal8Bit().
Note: on desktop Windows, qgetenv() 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.
Note: This function is thread-safe.
See also qputenv(), qEnvironmentVariable(), qEnvironmentVariableIsSet(), and 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: qputenv() was introduced because putenv() from the standard C library was deprecated in VC2005 (and later versions). qputenv() uses the replacement function in VC, and calls the standard C library's implementation on all other platforms.
See also qgetenv() and qEnvironmentVariable().
The qtTrId 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 QObject::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.
Note: This function is reentrant.
See also QObject::tr(), QCoreApplication::translate(), and Internationalization with Qt.
[since 5.1]
bool qunsetenv(const char *varName)
This function deletes the variable varName from the environment.
Returns true
on success.
This function was introduced in Qt 5.1.
See also qputenv(), qgetenv(), and qEnvironmentVariable().
[since 6.2]
PRIdQSIZETYPE
[since 6.2]
PRIiQSIZETYPE
See qsizetype.
This function was introduced in Qt 6.2.
[since 6.2]
PRIdQPTRDIFF
[since 6.2]
PRIiQPTRDIFF
See qptrdiff.
This function was introduced in Qt 6.2.
[since 6.2]
PRIXQUINTPTR
[since 6.2]
PRIoQUINTPTR
[since 6.2]
PRIuQUINTPTR
[since 6.2]
PRIxQUINTPTR
See quintptr.
This function was introduced in Qt 6.2.
[since 6.2]
PRIdQINTPTR
[since 6.2]
PRIiQINTPTR
See qintptr.
This function was introduced in Qt 6.2.
[since 6.2]
PRIXQUINTPTR
This function was introduced in Qt 6.2.
[since 6.2]
PRIdQINTPTR
This function was introduced in Qt 6.2.
[since 6.2]
PRIdQPTRDIFF
This function was introduced in Qt 6.2.
[since 6.2]
PRIdQSIZETYPE
This function was introduced in Qt 6.2.
[since 6.2]
PRIiQINTPTR
This function was introduced in Qt 6.2.
[since 6.2]
PRIiQPTRDIFF
This function was introduced in Qt 6.2.
[since 6.2]
PRIiQSIZETYPE
This function was introduced in Qt 6.2.
[since 6.2]
PRIoQUINTPTR
This function was introduced in Qt 6.2.
[since 6.2]
PRIuQUINTPTR
This function was introduced in Qt 6.2.
[since 6.2]
PRIxQUINTPTR
This function was introduced in Qt 6.2.
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 and 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.
[since 5.13]
QT_NO_DEPRECATED_WARNINGS
This macro can be used to suppress deprecation warnings that would otherwise be generated when using deprecated APIs.
This function was introduced in Qt 5.13.
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(); }
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(), and Internationalization with Qt.
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(), and Internationalization with Qt.
[since 5.12]
QT_TRANSLATE_N_NOOP3(context, sourceText, comment)
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); }
This function was introduced in Qt 5.12.
See also QT_TR_NOOP(), QT_TRANSLATE_NOOP(), QT_TRANSLATE_NOOP3(), and Internationalization with Qt.
[since 5.12]
QT_TRANSLATE_N_NOOP(context, sourceText)
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); }
This function was introduced in Qt 5.12.
See also QT_TRANSLATE_NOOP(), QT_TRANSLATE_N_NOOP3(), and Internationalization with Qt.
The QT_TRID_NOOP 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() and 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() and Internationalization with Qt.
[since 5.12]
QT_TR_N_NOOP(sourceText)
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); }
This function was introduced in Qt 5.12.
See also QT_TR_NOOP and 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 QT_VERSION macro will expand to 0x040102.
You can use QT_VERSION 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 and 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() and QT_VERSION.
Prints a warning message containing the source code file name and line number if test is false
.
Q_ASSERT() 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 Q_ASSERT 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(), and Debugging Techniques.
Prints the message what together with the location where, the source file name and line number if test is false
.
Q_ASSERT_X 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 Q_ASSERT_X 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(), and Debugging Techniques.
[since 5.0]
void Q_ASSUME(bool expr)
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
, Q_ASSUME 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, Q_ASSUME will tell the compiler that the current code execution cannot be reached. That is, Q_ASSUME(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. Q_ASSUME tells the compiler that it is the only possibility.
This function was introduced in Qt 5.0.
See also Q_ASSERT(), Q_UNREACHABLE(), and 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 and 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 Q_BYTE_ORDER 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 and 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 nullptr
, 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.
Q_CHECK_PTR does nothing if QT_NO_DEBUG
and QT_NO_EXCEPTIONS
were defined during compilation. Therefore you must not use Q_CHECK_PTR 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() and 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_RELOCATABLE_TYPE
specifies that Type has a constructor and/or a destructor but can be moved in memory using memcpy()
.Q_MOVABLE_TYPE
is the same as Q_RELOCATABLE_TYPE
. Prefer to use Q_RELOCATABLE_TYPE
in new code. 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 relocatable 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_RELOCATABLE_TYPE);
Qt will try to detect the class of a type using std::is_trivial_v<T> to identify primitive types and it will require both std::is_trivially_copyable_v<T> and std::is_trivially_destructible_v<T> to identify relocatable types. Use this macro to tune the behavior. For instance many types would be candidates for Q_RELOCATABLE_TYPE despite not being trivially-copyable.
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 declares a symbol to be an import from a shared library (see Creating Shared Libraries).
See also Q_DECL_EXPORT.
[since 5.0]
Q_DECL_NOEXCEPT
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.
This function was introduced in Qt 5.0.
See also Q_DECL_NOTHROW and Q_DECL_NOEXCEPT_EXPR().
[since 5.0]
Q_DECL_NOEXCEPT_EXPR(x)
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.
This function was introduced in Qt 5.0.
See also Q_DECL_NOTHROW and Q_DECL_NOEXCEPT.
[since 5.0]
Q_DECL_NOTHROW
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.
This function was introduced in Qt 5.0.
See also Q_DECL_NOEXCEPT and Q_DECL_NOEXCEPT_EXPR().
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.
[since 5.8]
void Q_FALLTHROUGH
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.
This function was introduced in Qt 5.8.
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().
[since 5.2]
Q_FORWARD_DECLARE_CF_TYPE(type)
Forward-declares a Core Foundation type. This includes the actual type and the ref type. For example, Q_FORWARD_DECLARE_CF_TYPE(CFString) declares __CFString and CFStringRef.
This function was introduced in Qt 5.2.
[since 5.2]
Q_FORWARD_DECLARE_MUTABLE_CF_TYPE(type)
Forward-declares a mutable Core Foundation type. This includes the actual type and the ref type. For example, Q_FORWARD_DECLARE_MUTABLE_CF_TYPE(CFMutableString) declares __CFMutableString and CFMutableStringRef.
This function was introduced in Qt 5.2.
[since 5.2]
Q_FORWARD_DECLARE_OBJC_CLASS(classname)
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.
This function was introduced in Qt 5.2.
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.
Q_FUNC_INFO 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 and 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 and 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 32-bit and 64-bit versions of Windows.
Defined on 64-bit versions of Windows.
Defined on all supported versions of Windows. That is, if Q_OS_WIN32 or Q_OS_WIN64 is defined.
This is a synonym for Q_OS_WIN.
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 QSysInfo::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 QSysInfo::buildCpuArchitecture().
Defined if the application is compiled for Alpha processors.
See also QSysInfo::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 QSysInfo::buildCpuArchitecture().
Defined if the application is compiled for ARMv5 processors. The Q_PROCESSOR_ARM macro is also defined when Q_PROCESSOR_ARM_V5 is defined.
See also QSysInfo::buildCpuArchitecture().
Defined if the application is compiled for ARMv6 processors. The Q_PROCESSOR_ARM and Q_PROCESSOR_ARM_V5 macros are also defined when Q_PROCESSOR_ARM_V6 is defined.
See also QSysInfo::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 Q_PROCESSOR_ARM_V7 is defined.
See also QSysInfo::buildCpuArchitecture().
Defined if the application is compiled for AVR32 processors.
See also QSysInfo::buildCpuArchitecture().
Defined if the application is compiled for Blackfin processors.
See also QSysInfo::buildCpuArchitecture().
Defined if the application is compiled for IA-64 processors. This includes all Itanium and Itanium 2 processors.
See also QSysInfo::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 QSysInfo::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 Q_PROCESSOR_MIPS_32 is defined.
See also QSysInfo::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 Q_PROCESSOR_MIPS_64 is defined.
See also QSysInfo::buildCpuArchitecture().
Defined if the application is compiled for MIPS-I processors. The Q_PROCESSOR_MIPS macro is also defined when Q_PROCESSOR_MIPS_I is defined.
See also QSysInfo::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 Q_PROCESSOR_MIPS_II is defined.
See also QSysInfo::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 Q_PROCESSOR_MIPS_III is defined.
See also QSysInfo::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 Q_PROCESSOR_MIPS_IV is defined.
See also QSysInfo::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 Q_PROCESSOR_MIPS_V is defined.
See also QSysInfo::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 QSysInfo::buildCpuArchitecture().
Defined if the application is compiled for 32-bit Power processors. The Q_PROCESSOR_POWER macro is also defined when Q_PROCESSOR_POWER_32 is defined.
See also QSysInfo::buildCpuArchitecture().
Defined if the application is compiled for 64-bit Power processors. The Q_PROCESSOR_POWER macro is also defined when Q_PROCESSOR_POWER_64 is defined.
See also QSysInfo::buildCpuArchitecture().
[since 5.13]
Q_PROCESSOR_RISCV
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.
This function was introduced in Qt 5.13.
See also QSysInfo::buildCpuArchitecture().
[since 5.13]
Q_PROCESSOR_RISCV_32
Defined if the application is compiled for 32-bit RISC-V processors. The Q_PROCESSOR_RISCV macro is also defined when Q_PROCESSOR_RISCV_32 is defined.
This function was introduced in Qt 5.13.
See also QSysInfo::buildCpuArchitecture().
[since 5.13]
Q_PROCESSOR_RISCV_64
Defined if the application is compiled for 64-bit RISC-V processors. The Q_PROCESSOR_RISCV macro is also defined when Q_PROCESSOR_RISCV_64 is defined.
This function was introduced in Qt 5.13.
See also QSysInfo::buildCpuArchitecture().
Defined if the application is compiled for S/390x processors. The Q_PROCESSOR_S390 macro is also defined when Q_PROCESSOR_S390_X is defined.
See also QSysInfo::buildCpuArchitecture().
Defined if the application is compiled for SuperH processors. Qt currently supports one SuperH revision: Q_PROCESSOR_SH_4A.
See also QSysInfo::buildCpuArchitecture().
Defined if the application is compiled for SuperH 4A processors. The Q_PROCESSOR_SH macro is also defined when Q_PROCESSOR_SH_4A is defined.
See also QSysInfo::buildCpuArchitecture().
Defined if the application is compiled for SPARC processors. Qt currently supports one optional SPARC revision: Q_PROCESSOR_SPARC_V9.
See also QSysInfo::buildCpuArchitecture().
Defined if the application is compiled for SPARC V9 processors. The Q_PROCESSOR_SPARC macro is also defined when Q_PROCESSOR_SPARC_V9 is defined.
See also QSysInfo::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 Q_PROCESSOR_X86_32 is defined.
See also QSysInfo::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 Q_PROCESSOR_X86_64 is defined.
See also QSysInfo::buildCpuArchitecture().
Wraps the unsigned 64-bit integer literal in a platform-independent way.
Example:
quint64 value = Q_UINT64_C(932838457459459);
See also quint64 and 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().
[since 5.0]
void Q_UNREACHABLE
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 Q_UNREACHABLE() 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.
This function was introduced in Qt 5.0.
See also Q_ASSERT(), Q_ASSUME(), and 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.
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().
Note: This function is thread-safe.
See also qDebug(), qInfo(), qWarning(), qFatal(), qInstallMessageHandler(), and 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().
Note: This function is thread-safe.
See also qInfo(), qWarning(), qCritical(), qFatal(), qInstallMessageHandler(), and Debugging Techniques.
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(), and Debugging Techniques.
[since 5.5]
qInfo(const char *message, ...)
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().
Note: This function is thread-safe.
This function was introduced in Qt 5.5.
See also qDebug(), qWarning(), qCritical(), qFatal(), qInstallMessageHandler(), and Debugging Techniques.
Returns str as a const char *
. This is equivalent to str.toLocal8Bit().constData().
The char pointer will be invalid after the statement in which qPrintable() is used. This is because the array returned by QString::toLocal8Bit() will fall out of scope.
Note: qDebug(), qInfo(), qWarning(), qCritical(), qFatal() expect %s arguments to be UTF-8 encoded, while qPrintable() converts to local 8-bit encoding. Therefore qUtf8Printable() should be used for logging strings instead of qPrintable().
See also qUtf8Printable().
[since 5.7]
const wchar_t *qUtf16Printable(const QString &str)
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 QString::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 qUtf16Printable() 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));
This function was introduced in Qt 5.7.
See also qPrintable(), qDebug(), qInfo(), qWarning(), qCritical(), and qFatal().
[since 5.4]
const char *qUtf8Printable(const QString &str)
Returns str as a const char *
. This is equivalent to str.toUtf8().constData().
The char pointer will be invalid after the statement in which qUtf8Printable() is used. This is because the array returned by QString::toUtf8() will fall out of scope.
Example:
qWarning("%s: %s", qUtf8Printable(key), qUtf8Printable(value));
This function was introduced in Qt 5.4.
See also qPrintable(), qDebug(), qInfo(), qWarning(), qCritical(), and qFatal().
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().
Note: This function is thread-safe.
See also qDebug(), qInfo(), qCritical(), qFatal(), qInstallMessageHandler(), and Debugging Techniques.
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Licensed under the GNU Free Documentation License, Version 1.3.
https://doc.qt.io/qt-6.2/qtglobal.html