[英]Macro evaluation in c preprocessor
I'd like to do something like this: 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__)
And I expected it to evaluate to "two args". 我期望它评估为“两个参数”。 But instead I have
但相反,我有
MYMACRONUM_ARGS()(1,1)
Is there a way to do what I want (using visual c++) ? 有没有办法做我想要的(使用visual c ++)?
PS Eventually I want to implement logger that dumps all of variables. PS最终我想实现转储所有变量的记录器。 The next code
下一个代码
int myInt = 7;
string myStr("Hello Galaxy!");
DUMP_VARS(myInt, myStr);
will produce log record "myInt = 7; myStr = Hello Galaxy!"
将产生日志记录
"myInt = 7; myStr = Hello Galaxy!"
You need another macro because macro expansion does not take place near #
or ##
: 您需要另一个宏,因为宏扩展不会发生在
#
或##
附近:
#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;
}
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. 如果你正在尝试这样做,但复杂的预处理技巧并不像其他人已经说过的那样真正安全,除非你真的需要,否则不要这样做。
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