<QtGlobal> - 全局 Qt 声明

<QtGlobal> 头文件包括基础全局声明。它被包括在大多数其它 Qt 头文件中。 更多...

Header: #include <QtGlobal>

类型

函数

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 )
QString qEnvironmentVariable (const char * varName , const QString & defaultValue )
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 )
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 )

QT_DEPRECATED_WARNINGS
QT_DISABLE_DEPRECATED_BEFORE
QT_NO_DEPRECATED_WARNINGS
QT_POINTER_SIZE
QT_REQUIRE_VERSION (int argc , char ** argv , const char * version )
QT_TRANSLATE_NOOP3 ( context , sourceText , disambiguation )
QT_TRANSLATE_NOOP ( context , sourceText )
QT_TRANSLATE_N_NOOP3 ( context , sourceText , comment )
QT_TRANSLATE_N_NOOP ( context , sourceText )
QT_TRID_NOOP ( id )
QT_TR_NOOP ( sourceText )
QT_TR_N_NOOP ( sourceText )
QT_VERSION
QT_VERSION_CHECK
QT_VERSION_STR
void Q_ASSERT (bool test )
void Q_ASSERT_X (bool test , const char * where , const char * what )
void Q_ASSUME (bool expr )
Q_BIG_ENDIAN
Q_BYTE_ORDER
Q_CC_BOR
Q_CC_CDS
Q_CC_CLANG
Q_CC_COMEAU
Q_CC_DEC
Q_CC_EDG
Q_CC_GHS
Q_CC_GNU
Q_CC_HIGHC
Q_CC_HPACC
Q_CC_INTEL
Q_CC_KAI
Q_CC_MIPS
Q_CC_MSVC
Q_CC_OC
Q_CC_PGI
Q_CC_SUN
Q_CC_SYM
Q_CC_USLC
Q_CC_WAT
void Q_CHECK_PTR (void * pointer )
Q_DECLARE_TYPEINFO ( Type , Flags )
Q_DECL_CONSTEXPR
Q_DECL_EXPORT
Q_DECL_IMPORT
Q_DECL_NOEXCEPT
Q_DECL_NOEXCEPT_EXPR ( x )
Q_DECL_NOTHROW
Q_DECL_RELAXED_CONSTEXPR
void Q_FALLTHROUGH
Q_FOREACH ( variable , container )
Q_FOREVER
Q_FORWARD_DECLARE_CF_TYPE ( type )
Q_FORWARD_DECLARE_MUTABLE_CF_TYPE ( type )
Q_FORWARD_DECLARE_OBJC_CLASS ( classname )
const char* Q_FUNC_INFO
qint64 Q_INT64_C ( literal )
Q_LIKELY ( expr )
Q_LITTLE_ENDIAN
Q_OS_AIX
Q_OS_ANDROID
Q_OS_BSD4
Q_OS_CYGWIN
Q_OS_DARWIN
Q_OS_FREEBSD
Q_OS_HPUX
Q_OS_HURD
Q_OS_IOS
Q_OS_LINUX
Q_OS_LYNX
Q_OS_MAC
Q_OS_MACOS
Q_OS_NETBSD
Q_OS_OPENBSD
Q_OS_OSX
Q_OS_QNX
Q_OS_SOLARIS
Q_OS_TVOS
Q_OS_UNIX
Q_OS_WASM
Q_OS_WATCHOS
Q_OS_WIN32
Q_OS_WIN64
Q_OS_WIN
Q_OS_WINDOWS
Q_PROCESSOR_X86
Q_PROCESSOR_S390
Q_PROCESSOR_ALPHA
Q_PROCESSOR_ARM
Q_PROCESSOR_ARM_V5
Q_PROCESSOR_ARM_V6
Q_PROCESSOR_ARM_V7
Q_PROCESSOR_AVR32
Q_PROCESSOR_BLACKFIN
Q_PROCESSOR_IA64
Q_PROCESSOR_MIPS
Q_PROCESSOR_MIPS_32
Q_PROCESSOR_MIPS_64
Q_PROCESSOR_MIPS_I
Q_PROCESSOR_MIPS_II
Q_PROCESSOR_MIPS_III
Q_PROCESSOR_MIPS_IV
Q_PROCESSOR_MIPS_V
Q_PROCESSOR_POWER
Q_PROCESSOR_POWER_32
Q_PROCESSOR_POWER_64
Q_PROCESSOR_RISCV
Q_PROCESSOR_RISCV_32
Q_PROCESSOR_RISCV_64
Q_PROCESSOR_S390_X
Q_PROCESSOR_SH
Q_PROCESSOR_SH_4A
Q_PROCESSOR_SPARC
Q_PROCESSOR_SPARC_V9
Q_PROCESSOR_X86_32
Q_PROCESSOR_X86_64
quint64 Q_UINT64_C ( literal )
Q_UNLIKELY ( expr )
void Q_UNREACHABLE
Q_UNUSED ( name )
foreach ( variable , container )
forever
qCritical (const char * message , ...)
qDebug (const char * message , ...)
qFatal (const char * message , ...)
qInfo (const char * message , ...)
const char * qPrintable (const QString & str )
const wchar_t * qUtf16Printable (const QString & str )
const char * qUtf8Printable (const QString & str )
qWarning (const char * message , ...)

详细描述

全局声明包括 types , 函数 and macros .

类型定义是基本类型的部分方便定义 (其中一些保证 Qt 支持的所有平台的某些位尺寸),部分类型有关 Qt 消息处理。函数有关生成消息、Qt 版本处理及比较/调节对象值。最后,某些声明宏使程序员能够向其应用程序添加编译器或平台特定代码,而其它的是用于更大操作的方便宏。

类型

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 在 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 类。

函数

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 () 和 qMax () respectively. All these functions return a corresponding template type; the template types can be replaced by any other type.

范例:

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 (),和 qFatal (). These functions call the message handler with the given message.

范例:

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

The remaining functions are qRound () 和 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 ,和 qVersion () function which returns the version number of Qt at run-time as a string.

<QtGlobal> 头文件提供一系列定义宏 (Q_CC_*) 若使用指定平台编译应用程序。例如, Q_CC_SUN 定义宏,若使用 Forte Developer 或 Sun Studio C++ 编译应用程序。头文件还为指定平台声明了一系列定义宏 (Q_OS_*)。例如, Q_OS_UNIX 是为基于 Unix 的系统定义的。

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 (),和 QT_TRANSLATE_NOOP3 () macros provide the possibility of marking strings for delayed translation. QT_TR_N_NOOP (), QT_TRANSLATE_N_NOOP (),和 QT_TRANSLATE_N_NOOP3 () are numerator dependent variants of these. The Q_ASSERT () 和 Q_ASSERT_X () enables warning messages of various level of refinement. The Q_FOREACH () 和 foreach () macros implement Qt's foreach loop.

Q_INT64_C () 和 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 qPrintable () 和 qUtf8Printable () macros represent an easy way of printing text.

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.

另请参阅 <QtAlgorithms> and QSysInfo .

类型文档编制

QFunctionPointer

这是 typedef 对于 void (*)() , a pointer to a function that takes no arguments and returns void.

[since 5.0] QtMessageHandler

这是采用以下签名的函数指针的 typedef:

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

该 typedef 在 Qt 5.0 引入。

另请参阅 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.

常量 描述
QtDebugMsg 0 生成的消息,由 qDebug () 函数。
QtInfoMsg 4 生成的消息,由 qInfo () 函数。
QtWarningMsg 1 生成的消息,由 qWarning () 函数。
QtCriticalMsg 2 生成的消息,由 qCritical () 函数。
QtFatalMsg 3 生成的消息,由 qFatal () 函数。
QtSystemMsg QtCriticalMsg

QtInfoMsg 在 Qt 5.5 添加。

另请参阅 QtMessageHandler and qInstallMessageHandler ().

qint8

Typedef 为 signed char 。此类型保证在 Qt 支持的所有平台为 8 位。

qint16

Typedef 为 signed short 。此类型保证在 Qt 支持的所有平台为 16 位。

qint32

Typedef 为 signed int 。此类型保证在 Qt 支持的所有平台为 32 位。

qint64

Typedef 为 long long int ( __int64 在 Windows)。此类型保证在 Qt 支持的所有平台为 64 位。

可以创建此类型的文字使用 Q_INT64_C () 宏:

qint64 value = Q_INT64_C(932838457459459);
							

另请参阅 Q_INT64_C (), quint64 ,和 qlonglong .

qintptr

用于以有符号整数表示指针的整型 (对哈希等有用)。

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.

另请参阅 qptrdiff , qint32 ,和 qint64 .

qlonglong

Typedef 为 long long int ( __int64 在 Windows)。这如同 qint64 .

另请参阅 qulonglong and qint64 .

qptrdiff

用于表示指针差异的整型。

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.

注意:qptrdiff 是有符号的。使用 quintptr 为无符号值。

另请参阅 quintptr , qint32 ,和 qint64 .

qreal

Typedef 为 double 除非配置 Qt 采用 -qreal float 选项。

[alias, since 5.10] qsizetype

Integral type providing Posix' ssize_t 对于所有平台。

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 对于无符号值。

该 typedef 在 Qt 5.10 引入。

另请参阅 qptrdiff .

quint8

Typedef 为 unsigned char 。此类型保证在 Qt 支持的所有平台为 8 位。

quint16

Typedef 为 unsigned short 。此类型保证在 Qt 支持的所有平台为 16 位。

quint32

Typedef 为 无符号 int 。此类型保证在 Qt 支持的所有平台为 32 位。

quint64

Typedef 为 unsigned long long int ( unsigned __int64 在 Windows)。此类型保证在 Qt 支持的所有平台为 64 位。

可以创建此类型的文字使用 Q_UINT64_C () 宏:

quint64 value = Q_UINT64_C(932838457459459);
							

另请参阅 Q_UINT64_C (), qint64 ,和 qulonglong .

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.

另请参阅 qptrdiff , quint32 ,和 quint64 .

qulonglong

Typedef 为 unsigned long long int ( unsigned __int64 在 Windows)。这如同 quint64 .

另请参阅 quint64 and qlonglong .

uchar

方便 typedef 为 unsigned char .

uint

方便 typedef 为 无符号 int .

ulong

方便 typedef 为 unsigned long .

ushort

方便 typedef 为 unsigned short .

函数文档编制

int qFpClassify ( double val )

int qFpClassify ( float val )

分类浮点值。

返回值的定义在 <cmath> : returns one of the following, determined by the floating-point class of val :

  • FP_NAN 非数字
  • FP_INFINITE 无穷大 (正值或负值)
  • FP_ZERO zero (positive or negative)
  • FP_NORMAL finite with a full mantissa
  • FP_SUBNORMAL finite with a reduced mantissa

QString qEnvironmentVariable (const char * varName )

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 () 和 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 ()

注意: 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.

注意: the variable name varName must contain only US-ASCII characters.

该函数在 Qt 5.10 引入。

另请参阅 qputenv (), qgetenv (), qEnvironmentVariableIsSet (),和 qEnvironmentVariableIsEmpty ().

template <typename T> T qAbs (const T & t )

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

范例:

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 )

返回 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.

该函数在 Qt 5.7 引入。

[since 5.7] template <typename T> void qAsConst (const T && t )

这是重载函数。

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
							

该函数在 Qt 5.7 引入。

template <typename T> const T & qBound (const T & min , const T & val , const T & max )

返回 val bounded by min and max 。这相当于 qMax ( min , qMin ( val , max )).

范例:

int myValue = 10;
int minValue = 2;
int maxValue = 6;
int boundedValue = qBound(minValue, myValue, maxValue);
// boundedValue == 6
							

另请参阅 qMin () 和 qMax ().

[since 5.7] template <typename T> auto qConstOverload ( T memberFunctionPointer )

返回 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)
							

该函数在 Qt 5.7 引入。

另请参阅 qOverload , qNonConstOverload ,和 基于字符串的连接和基于函子的连接之间的差异 .

QString qEnvironmentVariable (const char * varName )

QString qEnvironmentVariable (const char * varName , const QString & defaultValue )

[since 5.5] int qEnvironmentVariableIntValue (const char * varName , bool * ok = nullptr)

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

相当于

    qgetenv(varName).toInt(ok, 0)
							

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

注意: 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 .

该函数在 Qt 5.5 引入。

另请参阅 qgetenv (), qEnvironmentVariable (),和 qEnvironmentVariableIsSet ().

[since 5.1] bool qEnvironmentVariableIsEmpty (const char * varName )

Returns whether the environment variable varName is empty.

相当于

    qgetenv(varName).isEmpty()
							

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

该函数在 Qt 5.1 引入。

另请参阅 qgetenv (), qEnvironmentVariable (),和 qEnvironmentVariableIsSet ().

[since 5.1] bool qEnvironmentVariableIsSet (const char * varName )

Returns whether the environment variable varName 有设置。

相当于

    !qgetenv(varName).isNull()
							

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

该函数在 Qt 5.1 引入。

另请参阅 qgetenv (), qEnvironmentVariable (),和 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.

该函数在 Qt 5.14 引入。

[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
    }
							

该函数在 Qt 5.2 引入。

另请参阅 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.

该函数在 Qt 5.2 引入。

另请参阅 qFuzzyCompare ().

[since 5.4] QString qFormatLogMessage ( QtMsgType type , const QMessageLogContext & context , const QString & str )

Generates a formatted string out of the type , context , str 自变量。

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.

该函数在 Qt 5.4 引入。

另请参阅 qInstallMessageHandler () 和 qSetMessagePattern ().

int qFpClassify ( double val )

int qFpClassify ( float val )

bool qFuzzyCompare ( double p1 , double p2 )

比较浮点值 p1 and p2 并返回 true 若它们被认为相等,否则 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.

注意: 此函数是 thread-safe .

bool qFuzzyCompare ( float p1 , float p2 )

比较浮点值 p1 and p2 并返回 true 若它们被认为相等,否则 false .

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

注意: 此函数是 thread-safe .

bool qFuzzyIsNull ( double d )

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

注意: 此函数是 thread-safe .

bool qFuzzyIsNull ( float f )

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

注意: 此函数是 thread-safe .

double qInf ()

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

另请参阅 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) .

范例:

#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();
}
							

该函数在 Qt 5.0 引入。

另请参阅 QtMessageHandler , QtMsgType , qDebug (), qInfo (), qWarning (), qCritical (), qFatal (),和 调试技术 .

bool qIsFinite ( double d )

返回 true if the double d 是有限数。

bool qIsFinite ( float f )

返回 true if the float f 是有限数。

bool qIsInf ( double d )

返回 true if the double d 相当于无穷大。

另请参阅 qInf ().

bool qIsInf ( float f )

返回 true if the float f 相当于无穷大。

另请参阅 qInf ().

bool qIsNaN ( double d )

返回 true if the double d 是 NaN (非数字)。

bool qIsNaN ( float f )

返回 true if the float f 是 NaN (非数字)。

template <typename T> const T & qMax (const T & a , const T & b )

Returns the maximum of a and b .

范例:

int myValue = 6;
int yourValue = 4;
int maxValue = qMax(myValue, yourValue);
// maxValue == myValue
							

另请参阅 qMin () 和 qBound ().

template <typename T> const T & qMin (const T & a , const T & b )

Returns the minimum of a and b .

范例:

int myValue = 6;
int yourValue = 4;
int minValue = qMin(myValue, yourValue);
// minValue == yourValue
							

另请参阅 qMax () 和 qBound ().

[since 5.7] template <typename T> auto qNonConstOverload ( T memberFunctionPointer )

返回 memberFunctionPointer 指针指向非常量成员函数:

    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)
							

该函数在 Qt 5.7 引入。

另请参阅 qOverload ,qNonConstOverload,和 基于字符串的连接和基于函子的连接之间的差异 .

[since 5.7] template <typename T> auto qOverload ( T functionPointer )

返回重载函数指针。 模板参数是函数的自变量类型列表。 functionPointer 是指针指向 (成员) 函数:

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

若成员函数也是重载常量 qConstOverload and qNonConstOverload 需要用到。

qOverload() 要求启用 C++14。在仅 C++11 代码中,可以直接使用帮手类 QOverload、QConstOverload 及 QNonConstOverload:

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

注意: Qt 检测必要 C++ 14 编译器支持,通过特征测试推荐从 C++ 委员会标准文档 6 .

该函数在 Qt 5.7 引入。

另请参阅 qConstOverload (), qNonConstOverload (),和 基于字符串的连接和基于函子的连接之间的差异 .

double qQNaN ()

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

另请参阅 qIsNaN ().

qint64 qRound64 ( double d )

圆整 d 到最近 64 位整数。

Rounds half away from zero (e.g. 0.5 -> 1, -0.5 -> -1).

注意: This function does not guarantee correctness for high precisions.

范例:

double valueA = 42949672960.3;
double valueB = 42949672960.7;
qint64 roundedValueA = qRound64(valueA);
// roundedValueA = 42949672960
qint64 roundedValueB = qRound64(valueB);
// roundedValueB = 42949672961
							

qint64 qRound64 ( float d )

圆整 d 到最近 64 位整数。

Rounds half away from zero (e.g. 0.5f -> 1, -0.5f -> -1).

注意: This function does not guarantee correctness for high precisions.

范例:

float valueA = 42949672960.3;
float valueB = 42949672960.7;
qint64 roundedValueA = qRound64(valueA);
// roundedValueA = 42949672960
qint64 roundedValueB = qRound64(valueB);
// roundedValueB = 42949672961
							

int qRound ( double d )

圆整 d 到最近整数。

Rounds half away from zero (e.g. 0.5 -> 1, -0.5 -> -1).

注意: This function does not guarantee correctness for high precisions.

范例:

double valueA = 2.3;
double valueB = 2.7;
int roundedValueA = qRound(valueA);
// roundedValueA = 2
int roundedValueB = qRound(valueB);
// roundedValueB = 3
							

int qRound ( float d )

圆整 d 到最近整数。

Rounds half away from zero (e.g. 0.5f -> 1, -0.5f -> -1).

注意: This function does not guarantee correctness for high precisions.

范例:

float valueA = 2.3;
float 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.

[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 (),和 qFatal (). The category logging output of qCDebug (), qCInfo (), qCWarning (),和 qCCritical () is formatted, too.

Following placeholders are supported:

Placeholder 描述
%{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 被使用。
%{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.

范例:

    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}"
							

默认 pattern is "%{if-category}%{category}: %{endif}%{message}".

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.

注意: 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.

该函数在 Qt 5.0 引入。

另请参阅 qInstallMessageHandler (), 调试技术 ,和 QLoggingCategory .

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.

另请参阅 QT_VERSION_STR and QLibraryInfo::version ().

template <typename T> T * q_check_ptr ( T * p )

Uses Q_CHECK_PTR on p , then returns p .

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 作为 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 ().

注意: 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.

注意: 此函数是 thread-safe .

另请参阅 qputenv (), qEnvironmentVariable (), qEnvironmentVariableIsSet (),和 qEnvironmentVariableIsEmpty ().

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

此函数设置 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.

注意: 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.

另请参阅 qgetenv () 和 qEnvironmentVariable ().

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.

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

范例:

    //% "%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 工具。

警告: 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.

注意: 此函数是 可重入 .

另请参阅 QObject::tr (), QCoreApplication::translate (),和 Qt 国际化 .

[since 5.1] bool qunsetenv (const char * varName )

This function deletes the variable varName from the environment.

返回 true 当成功时。

该函数在 Qt 5.1 引入。

另请参阅 qputenv (), qgetenv (),和 qEnvironmentVariable ().

宏文档编制

QT_DEPRECATED_WARNINGS

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.

另请参阅 QT_DISABLE_DEPRECATED_BEFORE and QT_NO_DEPRECATED_WARNINGS .

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.

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.

另请参阅 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.

该函数在 Qt 5.13 引入。

另请参阅 QT_DISABLE_DEPRECATED_BEFORE .

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).

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").

范例:

#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 , disambiguation )

Marks the UTF-8 encoded string literal sourceText for delayed translation in the given context 采用给定 disambiguation 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 .

范例:

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);
}
							

另请参阅 QT_TR_NOOP (), QT_TRANSLATE_NOOP (),和 Qt 国际化 .

QT_TRANSLATE_NOOP ( context , sourceText )

Marks the UTF-8 encoded string literal sourceText for delayed translation in the given context 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 本身。

范例:

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]);
}
							

另请参阅 QT_TR_NOOP (), QT_TRANSLATE_NOOP3 (),和 Qt 国际化 .

[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 采用给定 comment 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 .

范例:

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);
}
							

该函数在 Qt 5.12 引入。

另请参阅 QT_TR_NOOP (), QT_TRANSLATE_NOOP (), QT_TRANSLATE_NOOP3 (),和 Qt 国际化 .

[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 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 本身。

范例:

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);
}
							

该函数在 Qt 5.12 引入。

另请参阅 QT_TRANSLATE_NOOP (), QT_TRANSLATE_N_NOOP3 (),和 Qt 国际化 .

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 .

范例:

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);
}
							

另请参阅 qtTrId () 和 Qt 国际化 .

QT_TR_NOOP ( sourceText )

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 本身。

范例:

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.

另请参阅 QT_TRANSLATE_NOOP () 和 Qt 国际化 .

[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 本身。

The macro expands to sourceText .

范例:

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);
}
							

该函数在 Qt 5.12 引入。

另请参阅 QT_TR_NOOP and Qt 国际化 .

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.

范例:

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

另请参阅 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.

范例:

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

另请参阅 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.

另请参阅 qVersion () 和 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.

范例:

// File: div.cpp
#include <QtGlobal>
int divide(int a, int b)
{
    Q_ASSERT(b != 0);
    return a / b;
}
							

b is zero, the Q_ASSERT statement will output the following message using the qFatal () 函数:

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

另请参阅 Q_ASSERT_X (), qFatal (),和 调试技术 .

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.

范例:

// File: div.cpp
#include <QtGlobal>
int divide(int a, int b)
{
    Q_ASSERT_X(b != 0, "divide", "division by zero");
    return a / b;
}
							

b is zero, the Q_ASSERT_X statement will output the following message using the qFatal () 函数:

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

另请参阅 Q_ASSERT (), qFatal (),和 调试技术 .

[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.

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.

注意: 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.

该函数在 Qt 5.0 引入。

另请参阅 Q_ASSERT (), Q_UNREACHABLE (),和 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
							

另请参阅 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
							

另请参阅 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_CLANG

Defined if the application is compiled using Clang.

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 )

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.

范例:

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

另请参阅 qWarning () 和 调试技术 .

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, 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 如同 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 对象。

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 indentify 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.

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.

另请参阅 Q_DECL_RELAXED_CONSTEXPR .

Q_DECL_EXPORT

This macro marks a symbol for shared library export (see 创建共享库 ).

另请参阅 Q_DECL_IMPORT .

Q_DECL_IMPORT

This macro declares a symbol to be an import from a shared library (see 创建共享库 ).

另请参阅 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 代替。

该函数在 Qt 5.0 引入。

另请参阅 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 代替。

该函数在 Qt 5.0 引入。

另请参阅 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 代替。

该函数在 Qt 5.0 引入。

另请参阅 Q_DECL_NOEXCEPT and Q_DECL_NOEXCEPT_EXPR ().

Q_DECL_RELAXED_CONSTEXPR

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.

另请参阅 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.

该函数在 Qt 5.8 引入。

另请参阅 Q_UNREACHABLE ().

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 变量。

注意: 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.

另请参阅 qAsConst ().

Q_FOREVER

如同 forever .

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

另请参阅 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.

该函数在 Qt 5.2 引入。

[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.

该函数在 Qt 5.2 引入。

[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.

该函数在 Qt 5.2 引入。

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.

范例:

qint64 value = Q_INT64_C(932838457459459);
							

另请参阅 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.

范例:

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

另请参阅 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
							

另请参阅 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_CYGWIN

Defined on Cygwin.

Q_OS_DARWIN

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

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_LINUX

Defined on Linux.

Q_OS_LYNX

Defined on LynxOS.

Q_OS_MAC

Deprecated synonym for Q_OS_DARWIN . Do not use.

Q_OS_MACOS

Defined on macOS.

Q_OS_NETBSD

Defined on NetBSD.

Q_OS_OPENBSD

Defined on OpenBSD.

Q_OS_OSX

Deprecated synonym for Q_OS_MACOS . Do not use.

Q_OS_QNX

Defined on QNX Neutrino.

Q_OS_SOLARIS

Defined on Sun Solaris.

Q_OS_TVOS

Defined on tvOS.

Q_OS_UNIX

Defined on Any UNIX BSD/SYSV system.

Q_OS_WASM

Defined on Web Assembly.

Q_OS_WATCHOS

Defined on watchOS.

Q_OS_WIN32

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

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 or Q_OS_WIN64 is defined.

Q_OS_WINDOWS

This is a synonym for Q_OS_WIN .

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 .

另请参阅 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 .

另请参阅 QSysInfo::buildCpuArchitecture ().

Q_PROCESSOR_ALPHA

Defined if the application is compiled for Alpha processors.

另请参阅 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 ,和 Q_PROCESSOR_ARM_V7 .

另请参阅 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.

另请参阅 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.

另请参阅 QSysInfo::buildCpuArchitecture ().

Q_PROCESSOR_ARM_V7

Defined if the application is compiled for ARMv7 processors. The Q_PROCESSOR_ARM , Q_PROCESSOR_ARM_V5 ,和 Q_PROCESSOR_ARM_V6 macros are also defined when Q_PROCESSOR_ARM_V7 is defined.

另请参阅 QSysInfo::buildCpuArchitecture ().

Q_PROCESSOR_AVR32

Defined if the application is compiled for AVR32 processors.

另请参阅 QSysInfo::buildCpuArchitecture ().

Q_PROCESSOR_BLACKFIN

Defined if the application is compiled for Blackfin processors.

另请参阅 QSysInfo::buildCpuArchitecture ().

Q_PROCESSOR_IA64

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

另请参阅 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 ,和 Q_PROCESSOR_MIPS_64 .

另请参阅 QSysInfo::buildCpuArchitecture ().

Q_PROCESSOR_MIPS_32

Defined if the application is compiled for MIPS32 processors. The Q_PROCESSOR_MIPS , Q_PROCESSOR_MIPS_I ,和 Q_PROCESSOR_MIPS_II macros are also defined when Q_PROCESSOR_MIPS_32 is defined.

另请参阅 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 ,和 Q_PROCESSOR_MIPS_V macros are also defined when Q_PROCESSOR_MIPS_64 is defined.

另请参阅 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.

另请参阅 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.

另请参阅 QSysInfo::buildCpuArchitecture ().

Q_PROCESSOR_MIPS_III

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

另请参阅 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 ,和 Q_PROCESSOR_MIPS_III macros are also defined when Q_PROCESSOR_MIPS_IV is defined.

另请参阅 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 ,和 Q_PROCESSOR_MIPS_IV macros are also defined when Q_PROCESSOR_MIPS_V is defined.

另请参阅 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 .

另请参阅 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.

另请参阅 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.

另请参阅 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 .

该函数在 Qt 5.13 引入。

另请参阅 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.

该函数在 Qt 5.13 引入。

另请参阅 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.

该函数在 Qt 5.13 引入。

另请参阅 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.

另请参阅 QSysInfo::buildCpuArchitecture ().

Q_PROCESSOR_SH

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

另请参阅 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.

另请参阅 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 .

另请参阅 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.

另请参阅 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.

另请参阅 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.

另请参阅 QSysInfo::buildCpuArchitecture ().

quint64 Q_UINT64_C ( literal )

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

范例:

quint64 value = Q_UINT64_C(932838457459459);
							

另请参阅 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.

范例:

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;
}
							

另请参阅 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.

该函数在 Qt 5.0 引入。

另请参阅 Q_ASSERT (), Q_ASSUME (),和 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 foreach 关键字 了解细节。

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

CONFIG += no_keywords
							

注意: 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.

另请参阅 qAsConst ().

forever

This macro is provided for convenience for writing infinite loops.

范例:

forever {
    ...
}
							

它相当于 for (;;) .

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

CONFIG += no_keywords
							

另请参阅 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 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.

范例:

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 ().

注意: 此函数是 thread-safe .

另请参阅 qDebug (), qInfo (), qWarning (), qFatal (), qInstallMessageHandler (),和 调试技术 .

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 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.

范例:

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 ().

注意: 此函数是 thread-safe .

另请参阅 qInfo (), qWarning (), qCritical (), qFatal (), qInstallMessageHandler (),和 调试技术 .

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 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.

范例:

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 ().

另请参阅 qDebug (), qInfo (), qWarning (), qCritical (), qInstallMessageHandler (),和 调试技术 .

[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.

范例:

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 ().

注意: 此函数是 thread-safe .

该函数在 Qt 5.5 引入。

另请参阅 qDebug (), qWarning (), qCritical (), qFatal (), qInstallMessageHandler (),和 调试技术 .

const char * qPrintable (const QString & str )

返回 str 作为 const char * 。这相当于 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.

注意: 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().

另请参阅 qUtf8Printable ().

[since 5.7] const wchar_t * qUtf16Printable (const QString & str )

返回 str 作为 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.

范例:

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

该函数在 Qt 5.7 引入。

另请参阅 qPrintable (), qDebug (), qInfo (), qWarning (), qCritical (),和 qFatal ().

[since 5.4] const char * qUtf8Printable (const QString & str )

返回 str 作为 const char * 。这相当于 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.

范例:

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

该函数在 Qt 5.4 引入。

另请参阅 qPrintable (), qDebug (), qInfo (), qWarning (), qCritical (),和 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 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.

范例:

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 ().

注意: 此函数是 thread-safe .

另请参阅 qDebug (), qInfo (), qCritical (), qFatal (), qInstallMessageHandler (),和 调试技术 .