QT common macro definitions

This article mainly accumulates some commonly used macros Definition , Some definitions are in the header file QtGlobal in

1. QT_VERSION ,QT_VERSION_CHECK

// It is mainly used for conditional compilation settings , according to Qt Different versions compile different code 
// I used it here Qt The version is 5.7.1, So the branch of software is cc = 10000
 Sample code ：
#if QT_VERSION >= QT_VERSION_CHECK(5,7,2) 
    int cc = 0;
#else
    int cc = 10000;
#endif

2. QT_VERSION_STR

qDebug() << QT_VERSION_STR << endl;

3. Q_BYTE_ORDER,Q_BIG_ENDIAN,Q_LITTLE_ENDIAN
System memory data byte order , Indicates the size end

#if Q_BYTE_ORDER == Q_LITTLE_ENDIAN // My platform is small end 
    qDebug() << "Q_LITTLE_ENDIAN" << endl;
#else

#endif

4. debug Output Disable setting macro QT_NO_DEBUG_OUTPUT, stay pro Add the following code to the file , All in the software QDebug Will fail

 DEFINES += QT_NO_DEBUG_OUTPUT

5. Q_UNUSED(valuename) Used for variables not used in functions , Tell the compiler that this variable does not require an alarm
   Special , It can also be in pro Add the following code to the file to shield unused alarms

QMAKE_CXXFLAGS += -Wno-unused-parameter

7. Q_DECL_OVERRIDE After the function declaration for the class , Overloading a virtual function , If this macro is used , No overload operation was performed , The compiler will report an error

8. Q_DECL_FINAL Used to define a virtual function as the final level , Can no longer be overloaded , Or define a class that can no longer be inherited

class QPushButton Q_DECL_FINAL {
      //QPushButton  Can no longer be inherited 
	//...
};

9. Q_SIGNAL： Unwanted signals Keyword can specify a function as singal function

10. Q_SLOT： Unwanted slots Keyword can specify a function as slot function

11. qChecksum： The calculation is based on CRC-16-CCITT Algorithm CRC-16 Check code

12. qCompress/qUncompress： be based on zlib The algorithm compresses the byte buffer / decompression , You can customize the compression ratio

13. qDeleteAll： Each object in a container or iterator is delete operation

14. qRound/qRound64： Round floating point numbers , rounding

15. qFuzzyCompare： Fuzzy comparison of thread safe floating point numbers , The problem of floating-point precision error is solved

16. qVersion： Get the currently running Qt Version number of

17. QSysInfo： Get the current running system information , Including version number, etc ,Mac/Symbian/Windows All apply

18. QtEndian： Handle the problem of different byte storage order under different architectures

19. QObject::findChildren<>： Find hidden sub objects

20. qobject_cast： No compiler needed RTTI With the support of C++ Standard library dynamic_cast The function of

21. QObject::deleteLater： Call... In the event handling loop , Delete yourself at the end of the event processing cycle ; Call... Outside the event handling loop , Delete yourself at the beginning of the next event processing cycle

22. qPrintable： similar QString::toLocal8Bit()::constData(), But it's better to remember

23. connect(SomeObj, SIGNAL(foo()), SIGNAL(bar())： Through one signal Automatically trigger another signal.