C++ 宏中的“#ifdef”
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"#ifdef" inside a macro
提问by JasonGenX
Possible Duplicate:
#ifdef inside #define
可能重复：
#ifdef 内 #define
How do I use the character "#" successfully inside a Macro? It screams when I do something like that:
如何在宏中成功使用字符“#”？当我做这样的事情时它会尖叫：
#define DO(WHAT) \
#ifdef DEBUG \
MyObj->WHAT() \
#endif \
回答by Roger Lipscombe
You can't do that. You have to do something like this:
你不能那样做。你必须做这样的事情：
#ifdef DEBUG
#define DO(WHAT) MyObj->WHAT()
#else
#define DO(WHAT) do { } while(0)
#endif
The do { } while(0)avoids empty statements. See this question, for example.
在do { } while(0)避免了空语句。例如，请参阅此问题。
回答by Oliver Charlesworth
It screams because you can't do that.
它尖叫是因为你不能那样做。
I suggest the following as an alternative:
我建议以下作为替代方案：
#ifdef DEBUG
#define DO(WHAT) MyObj->WHAT()
#else
#define DO(WHAT)
#endif
回答by Paul Manta
It seems that what you want to do can be achieved like this, without running into any problems:
看来你想做的事情可以这样实现，不会遇到任何问题：
#ifdef DEBUG
# define DO(WHAT) MyObj->WHAT()
#else
# define DO(WHAT) while(false)
#endif
Btw, better use the NDEBUGmacro, unless you have a more specific reason not to. NDEBUGis more widely used as a macro that means no-debugging. For example the standard assertmacro can be disabled by defining NDEBUG. Your code would become:
顺便说一句，最好使用NDEBUG宏，除非您有更具体的理由不这样做。NDEBUG更广泛地用作宏，这意味着无需调试。例如，assert可以通过定义来禁用标准宏NDEBUG。你的代码会变成：
#ifndef NDEBUG
# define DO(WHAT) MyObj->WHAT()
#else
# define DO(WHAT) while(false)
#endif
回答by antlersoft
You can do the same thing like this:
你可以做同样的事情：
#ifdef DEBUG
#define DO(WHAT) MyObj->WHAT()
#else
#define DO(WHAT)
#endif
回答by Miguel
How about:
怎么样：
#ifdef DEBUG
#define DO(WHAT) MyObj->WHAT()
#else
#define DO(WHAT)
#endif
