C预处理器中的宏评估 [英] Macro evaluation in c preprocessor

问题描述

我想做这样的事情：

#define NUM_ARGS() 2
#define MYMACRO0(...) "no args"
#define MYMACRO1(...) "one arg"
#define MYMACRO2(...) "two args"
#define MYMACRO(num,...) MYMACRO##num(__VA_ARGS__)
#define GENERATE(...) MYMACRO(NUM_ARGS(),__VA_ARGS__)

我希望它的计算结果为两个参数。
但是我有

And I expected it to evaluate to "two args". But instead I have

MYMACRONUM_ARGS()(1,1)

有没有一种方法可以做我想要的事情（使用Visual C ++）？

Is there a way to do what I want (using visual c++) ?

PS
最后，我想实现转储所有变量的记录器。下一个代码

P.S. Eventually I want to implement logger that dumps all of variables. The next code

int myInt = 7;
string myStr("Hello Galaxy!");
DUMP_VARS(myInt, myStr);

将生成日志记录 myInt = 7; myStr = Hello Galaxy！

推荐答案

您需要另一个宏，因为宏扩展不会在附近进行＃或 ## ：

You need another macro because macro expansion does not take place near # or ##:

#define NUM_ARGS() 2
#define MYMACRO0(...) "no args"
#define MYMACRO1(...) "one arg"
#define MYMACRO2(...) "two args"
#define MYMACRO_AUX(num,...) MYMACRO##num(__VA_ARGS__)
#define MYMACRO(num,...) MYMACRO_AUX(num, __VA_ARGS__)
#define GENERATE(...) MYMACRO(NUM_ARGS(),__VA_ARGS__)

#include <stdio.h>

int main(void)
{
    puts(GENERATE(0, 1));

    return 0;
}

如果这是您要尝试执行的操作，但复杂的预处理器技巧是就像别人已经说过的那样，不是很安全，除非确实需要，否则不要这样做。

If this is what you're trying to do, but complicated preprocessor tricks are not really safe, as others already said, don't do it unless you really have to.

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