恰当的C preprocessor宏观空操作 [英] Proper C preprocessor macro no-op

问题描述

有关调试日志记录，我经常看到并使用类似

For debug logging, I have often seen and used something like

#ifdef DEBUG
    #define DLOG(fmt, args...) printf("%s:%d "fmt,__FILE__,__LINE__,args)
#else
    #define DLOG(fmt, args...)
#endif

但在一些地方，我看到了第二个的#define 与

#define DLOG(fmt, args...) do {} while (0)

在特定的，有这个答案和上的这对方的回答以同样的问题表明，这个问题将在一个类似的情况。

In particular, there's this answer, and the comment on this other answer to the same question suggests that the problem would be in a situation like

if (condition)
    DLOG("foo");

虽然我的快速测试表明，本身就行所产生的分号将作为条件内无操作的语句。

though my quick test suggests that the resulting semicolon on the line by itself will serve as the no-op statement inside the conditional.

是一个或其他的的任何和做{}而（0）更好？如果是这样，为什么？有没有别的东西，甚至更好？

Is one or the other of nothing and do {} while (0) better? If so, why? Is there something else that's even better?

推荐答案

请参阅C ＃定义宏调试印刷了解为什么需要不同形式的无操作的解释。你想拥有，当你不使用它的编译器解析调试印刷code即便这样的错误不蠕变

See C #define macro for debug printing for an explanation of why you want a different form of no-op. You want to have the compiler parse the debug printing code even when you aren't using it so that errors do not creep in.

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