在将Qt5应用程序返回到Qt4时替换Q_NULLPTR ?

My application may be used on systems that are still defaulting to Qt4.x rather than Qt5.x and I was trying to do a "quick and dirty" port of a version that would compile/link and run with either major version of the libraries. I was wondering what would be the best way to get around the absence of Q_NULLPTR in Qt4.x? I saw the link mentioned in this SO answer which indicated the definition as:

我的应用程序可以在仍然默认为Qt4的系统上使用。而不是Qt5 x。我和x试图做一个“快速而肮脏”的版本端口，该版本将编译/链接并运行于库的任何一个主要版本。我想知道在Qt4.x中绕过Q_NULLPTR的最好方法是什么?我看到了这个答案中提到的联系它表明了定义是:

#ifdef Q_COMPILER_NULLPTR
# define Q_NULLPTR         nullptr
#else
# define Q_NULLPTR         NULL
#endif

So should I just use a:

我应该用a:

contains(QT_MAJOR_VERSION, 4) {
DEFINES += Q_NULLPTR=NULL
}

in my qmake project file?

在我的qmake项目文件中?

1 个解决方案

#1

Q_NULLPTR is Qt’s way to support both C++11 capable compilers as well as older C++98/03 ones. Do you actually need that level of sophistication? If not, then just use NULL, 0 or nullptr directly, depending on your compiler.

Q_NULLPTR是Qt的方法，它既支持c++ 11的编译器，也支持旧的c++ 98/03的编译器。你真的需要那种复杂的程度吗?如果不是，那么直接使用NULL, 0或nullptr，这取决于您的编译器。

Otherwise things get more complicated because you need to detect the currently active C++ version. See edit below.

否则事情会变得更复杂，因为您需要检测当前活动的c++版本。请参阅下面的编辑。

Of course you can always choose the easy way and use NULL or 0 which works in all versions of C++.

当然，您可以选择简单的方法并使用NULL或0，这在c++的所有版本中都适用。

Edit

编辑

To mimic Qt5’s behaviour you could use this:

要模仿Qt5的行为，您可以使用以下方法:

#if __cplusplus >= 201103L
    #define Q_NULLPTR nullptr
#else
    // not NULL to stay consistent with Qt’s convention
    #define Q_NULLPTR 0
#endif

Including a header just to have access to Q_NULLPTR isn’t terribly great, so you’ll probably want to define that macro in a .pro file. However, I don’t know how to detect the active C++ version with Qt4’s QMake.

包括一个仅能访问Q_NULLPTR的头并不太好，因此您可能需要在.pro文件中定义该宏。但是，我不知道如何使用Qt4的QMake检测活动c++版本。

#1