<QtGlobal> - Global Qt Declarations

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

• Obsolete members

Types

Functions

Macros

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

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

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

See also <QtAlgorithms> and QSysInfo.

Type Documentation

typedef QFunctionPointer

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

typedef 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().

enum QtMsgType

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.

See also QtMessageHandler and qInstallMessageHandler().

typedef qint8

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

typedef qint16

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

typedef qint32

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

typedef qint64

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, and qlonglong.

typedef qintptr

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, and qint64.

typedef qlonglong

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

See also qulonglong and qint64.

typedef qptrdiff

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, and qint64.

typedef qreal

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

typedef quint8

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

typedef quint16

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

typedef quint32

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

typedef quint64

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, and qulonglong.

typedef quintptr

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, and quint64.

typedef qulonglong

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

See also quint64 and qlonglong.

typedef uchar

Convenience typedef for unsigned char.

typedef uint

Convenience typedef for unsigned int.

typedef ulong

Convenience typedef for unsigned long.

typedef ushort

Convenience typedef for unsigned short.

Function Documentation

T qAbs(const T & value)

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

Example:

int absoluteValue;
int myValue = -4;

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

const T & qBound(const T & min, const T & value, const T & max)

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

Example:

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

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

See also qMin() and qMax().

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() and qEnvironmentVariableIsSet().

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() and qEnvironmentVariableIsEmpty().

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().

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().

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().

[static] bool qFuzzyCompare(double p1, double p2)

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. The solution to this is to compare against values greater than or equal to 1.0.

        // 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.

This function was introduced in Qt 4.4.

[static] bool qFuzzyCompare(float p1, float p2)

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.

This function was introduced in Qt 4.4.

double qInf()

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

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();
    switch (type) {
    case QtDebugMsg:
        fprintf(stderr, "Debug: %s (%s:%u, %s)\n", localMsg.constData(), context.file, context.line, context.function);
        break;
    case QtWarningMsg:
        fprintf(stderr, "Warning: %s (%s:%u, %s)\n", localMsg.constData(), context.file, context.line, context.function);
        break;
    case QtCriticalMsg:
        fprintf(stderr, "Critical: %s (%s:%u, %s)\n", localMsg.constData(), context.file, context.line, context.function);
        break;
    case QtFatalMsg:
        fprintf(stderr, "Fatal: %s (%s:%u, %s)\n", localMsg.constData(), context.file, context.line, context.function);
        abort();
    }
}

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(), qWarning(), qCritical(), qFatal(), and Debugging Techniques.

bool qIsFinite(double d)

Returns true if the double d is a finite number.

bool qIsFinite(float f)

Returns true if the float f is a finite number.

bool qIsInf(double d)

Returns true if the double d is equivalent to infinity.

bool qIsInf(float f)

Returns true if the float f is equivalent to infinity.

bool qIsNaN(double d)

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

bool qIsNaN(float f)

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

const T & qMax(const T & value1, const T & value2)

Returns the maximum of value1 and value2.

Example:

int myValue = 6;
int yourValue = 4;

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

See also qMin() and qBound().

const T & qMin(const T & value1, const T & value2)

Returns the minimum of value1 and value2.

Example:

int myValue = 6;
int yourValue = 4;

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

See also qMax() and qBound().

double qQNaN()

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

qint64 qRound64(qreal value)

Rounds value to the nearest 64-bit integer.

Example:

qreal valueA = 42949672960.3;
qreal valueB = 42949672960.7;

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

int qRound(qreal value)

Rounds value to the nearest integer.

Example:

qreal valueA = 2.3;
qreal valueB = 2.7;

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

double qSNaN()

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

void qSetMessagePattern(const QString & pattern)

Changes the output of the default message handler.

Allows to tweak the output of qDebug(), qWarning(), qCritical() and qFatal().

Following placeholders are supported:

You can also use conditionals on the type of the message using %{if-debug}, %{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-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.

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

This function was introduced in Qt 5.0.

See also qInstallMessageHandler() and Debugging Techniques.

const char * qVersion()

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.

T * q_check_ptr(T * pointer)

Uses Q_CHECK_PTR on pointer, then returns pointer.

This can be used as an inline version of Q_CHECK_PTR.

QByteArray qgetenv(const char * varName)

Returns the value of the environment variable with name varName. To get the variable string, use QByteArray::constData().

Note: qgetenv() was introduced because getenv() from the standard C library was deprecated in VC2005 (and later versions). qgetenv() uses the new replacement function in VC, and calls the standard C library's implementation on all other platforms.

See also qputenv(), qEnvironmentVariableIsSet(), and qEnvironmentVariableIsEmpty().

bool qputenv(const char * varName, const QByteArray & value)

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().

int qrand()

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.

This function was introduced in Qt 4.2.

See also qsrand().

void qsrand(uint seed)

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 calls qrand(), the threads will get the same random number sequence.

This function was introduced in Qt 4.2.

See also qrand().

QString qtTrId(const char * id, int n = -1)

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.

This function was introduced in Qt 4.6.

See also QObject::tr(), QCoreApplication::translate(), and Internationalization with Qt.

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() and qgetenv().

Macro Documentation

QT_DISABLE_DEPRECATED_BEFORE

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.

Examples: 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 any functions, including the ones deprecated in Qt 5.0

QT_POINTER_SIZE

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.

QT_REQUIRE_VERSION(int argc, char ** argv, const char * version)

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();
}

QT_TRANSLATE_NOOP3( context, sourceText, comment)

Marks the string literal sourceText for dynamic translation in the given context and with comment, i.e the stored sourceText will not be altered. The context is typically a class and also needs to be specified as string literal. The string literal comment will be available for translators using e.g. Qt Linguist.

The macro expands to anonymous struct of the two string literals passed as sourceText and comment.

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);
}

This function was introduced in Qt 4.4.

See also QT_TR_NOOP(), QT_TRANSLATE_NOOP(), and Internationalization with Qt.

QT_TRANSLATE_NOOP( context, sourceText)

Marks the string literal sourceText for dynamic translation in the given context; i.e, the stored sourceText will not be altered. The context is typically a class and also needs to be specified as string literal.

The macro expands to sourceText.

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.

QT_TRID_NOOP( id)

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);
}

This function was introduced in Qt 4.6.

See also qtTrId() and Internationalization with Qt.

QT_TR_NOOP( sourceText)

Marks the string literal sourceText for dynamic translation in the current context (class), i.e the stored sourceText will not be altered.

The macro expands to sourceText.

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 except that it tells lupdate that the source string is encoded in UTF-8. Corresponding variants exist in the QT_TRANSLATE_NOOP() family of macros, too.

See also QT_TRANSLATE_NOOP() and Internationalization with Qt.

QT_VERSION

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().

QT_VERSION_CHECK

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.

QT_VERSION_STR

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.

void Q_ASSERT(bool test)

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.

void Q_ASSERT_X(bool test, const char * where, const char * what)

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.

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().

Q_BIG_ENDIAN

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.

Q_BYTE_ORDER

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.

Q_CC_BOR

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

Q_CC_CDS

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

Q_CC_COMEAU

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

Q_CC_DEC

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

Q_CC_EDG

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

Q_CC_GHS

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

Q_CC_GNU

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

Q_CC_HIGHC

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

Q_CC_HPACC

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

Q_CC_INTEL

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

Q_CC_KAI

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

Q_CC_MIPS

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

Q_CC_MSVC

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

Q_CC_OC

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

Q_CC_PGI

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

Q_CC_SUN

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

Q_CC_SYM

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

Q_CC_USLC

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

Q_CC_WAT

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

void Q_CHECK_PTR(void * pointer)

If pointer is 0, prints a warning message containing the source code's file name and line number, saying that the program ran out of memory.

Q_CHECK_PTR does nothing if QT_NO_DEBUG was defined during compilation.

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.

Q_DECLARE_TYPEINFO( Type, Flags)

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, or else a type where every bit pattern is a valid object and memcpy() 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().
• 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);

Q_DECL_CONSTEXPR

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.

Q_DECL_EXPORT

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

See also Q_DECL_IMPORT.

Q_DECL_FINAL

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" if your compiler supports that C++11 contextual keyword, or something non-standard if your compiler supports something close enough to the C++11 semantics, or to nothing otherwise.

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*) Q_DECL_FINAL;

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

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

This function was introduced in Qt 5.0.

See also Q_DECL_OVERRIDE.

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.

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().

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.

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().

Q_DECL_OVERRIDE

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" if your compiler supports that C++11 contextual keyword, or to nothing otherwise.

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*) Q_DECL_OVERRIDE;

This function was introduced in Qt 5.0.

See also Q_DECL_FINAL.

Q_FOREACH( variable, container)

Same as foreach(variable, container).

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

See also foreach().

Q_FOREVER

Same as forever.

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

See also foreach().

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.

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.

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.

const char * Q_FUNC_INFO()

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.

qint64 Q_INT64_C( literal)

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().

Q_LIKELY( expr)

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))) {
            ...
        }
        ...
    }

This function was introduced in Qt 4.8.

See also Q_UNLIKELY().

Q_LITTLE_ENDIAN

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.

Q_OS_AIX

Defined on AIX.

Q_OS_ANDROID

Defined on Android.

Q_OS_BSD4

Defined on Any BSD 4.4 system.

Q_OS_BSDI

Defined on BSD/OS.

Q_OS_CYGWIN

Defined on Cygwin.

Q_OS_DARWIN

Defined on Darwin-based operating systems such as OS X and iOS, including any open source version(s) of Darwin.

Q_OS_DGUX

Defined on DG/UX.

Q_OS_DYNIX

Defined on DYNIX/ptx.

Q_OS_FREEBSD

Defined on FreeBSD.

Q_OS_HPUX

Defined on HP-UX.

Q_OS_HURD

Defined on GNU Hurd.

Q_OS_IOS

Defined on iOS.

Q_OS_IRIX

Defined on SGI Irix.

Q_OS_LINUX

Defined on Linux.

Q_OS_LYNX

Defined on LynxOS.

Q_OS_MAC

Defined on Darwin-based operating systems distributed by Apple, which currently includes OS X and iOS, but not the open source version.

Q_OS_NETBSD

Defined on NetBSD.

Q_OS_OPENBSD

Defined on OpenBSD.

Q_OS_OSF

Defined on HP Tru64 UNIX.

Q_OS_OSX

Defined on OS X.

Q_OS_QNX

Defined on QNX Neutrino.

Q_OS_RELIANT

Defined on Reliant UNIX.

Q_OS_SCO

Defined on SCO OpenServer 5.

Q_OS_SOLARIS

Defined on Sun Solaris.

Q_OS_ULTRIX

Defined on DEC Ultrix.

Q_OS_UNIX

Defined on Any UNIX BSD/SYSV system.

Q_OS_UNIXWARE

Defined on UnixWare 7, Open UNIX 8.

Q_OS_WIN32

Defined on 32-bit and 64-bit versions of Windows (not on Windows CE).

Q_OS_WIN64

Defined on 64-bit versions of Windows.

Q_OS_WIN

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

Q_OS_WINCE

Defined on Windows CE.

Q_OS_WINPHONE

Defined on Windows Phone 8.

Q_OS_WINRT

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

Q_PROCESSOR_X86

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().

Q_PROCESSOR_S390

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().

Q_PROCESSOR_ALPHA

Defined if the application is compiled for Alpha processors.

See also QSysInfo::buildCpuArchitecture().

Q_PROCESSOR_ARM

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().

Q_PROCESSOR_ARM_V5

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().

Q_PROCESSOR_ARM_V6

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().

Q_PROCESSOR_ARM_V7

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().

Q_PROCESSOR_AVR32

Defined if the application is compiled for AVR32 processors.

See also QSysInfo::buildCpuArchitecture().

Q_PROCESSOR_BLACKFIN

Defined if the application is compiled for Blackfin processors.

See also QSysInfo::buildCpuArchitecture().

Q_PROCESSOR_IA64

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

See also QSysInfo::buildCpuArchitecture().

Q_PROCESSOR_MIPS

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().

Q_PROCESSOR_MIPS_32

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().

Q_PROCESSOR_MIPS_64

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().

Q_PROCESSOR_MIPS_I

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().

Q_PROCESSOR_MIPS_II

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().

Q_PROCESSOR_MIPS_III

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().

Q_PROCESSOR_MIPS_IV

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().

Q_PROCESSOR_MIPS_V

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().

Q_PROCESSOR_POWER

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().

Q_PROCESSOR_POWER_32

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().

Q_PROCESSOR_POWER_64

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().

Q_PROCESSOR_S390_X

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().

Q_PROCESSOR_SH

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

See also QSysInfo::buildCpuArchitecture().

Q_PROCESSOR_SH_4A

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().

Q_PROCESSOR_SPARC

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

See also QSysInfo::buildCpuArchitecture().

Q_PROCESSOR_SPARC_V9

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().

Q_PROCESSOR_X86_32

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().

Q_PROCESSOR_X86_64

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().

quint64 Q_UINT64_C( literal)

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().

Q_UNLIKELY( expr)

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;
}

This function was introduced in Qt 4.8.

See also Q_LIKELY().

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().

Q_UNUSED( name)

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.

foreach( variable, container)

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

See also Q_FOREACH().

forever

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.

qCritical(const char * message, ...)

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 Blackberry 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(), qWarning(), qFatal(), qInstallMessageHandler(), and Debugging Techniques.

qDebug(const char * message, ...)

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 Blackberry 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 qWarning(), qCritical(), qFatal(), qInstallMessageHandler(), and Debugging Techniques.

qFatal(const char * message, ...)

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 Blackberry the message is sent to slogger2.

If you are using the default message handler this function will abort on Unix systems 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(), qCritical(), qWarning(), qInstallMessageHandler(), and Debugging Techniques.

qMove( x)

It expands to "std::move" if your compiler supports that C++11 function, or to nothing otherwise.

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

const char * qPrintable(const QString & str)

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(), 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().

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(), qWarning(), qCritical(), and qFatal().

qWarning(const char * message, ...)

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 Blackberry the message is sent to slogger2. This function does nothing if QT_NO_WARNING_OUTPUT was defined during compilation; it exits if the environment variable QT_FATAL_WARNINGS 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 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(), qCritical(), qFatal(), qInstallMessageHandler(), and Debugging Techniques.