C++ Macro containing #ifdef

Question

I am trying to define a C++ macro that contains an #ifdef. However, the preprocessor complains that it expects an expression when I use PRINT_PRETTY_FUNCTION.

#define PRINT_PRETTY_FUNCTION \
    #ifdef PRINT_FUNC_NAMES \
    printf("%s\n", __PRETTY_FUNCTION__); \
    #endif

Does C++ allow for such a macro definition?

littleadv · Answer 1 · 2022-01-10T06:05:39.763

0

#ifdef should be first in its line. It is not in your case.

These are directives to the pre-processor which only does one pass evaluating the macro (once expanded the preprocessor won't look at it again), so you just can't do what you're trying to do.

Also see this nice answer.

edited Jan 10 '22 at 06:05

answered Jan 10 '22 at 05:58

littleadv

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I wanted the compiler to just replace `PRINT_PRETTY_FUNCTION` with the `#ifdef`. – afp_2008 Jan 10 '22 at 06:02
1

That's the thing - it's not the compiler that's doing the replacing, it's the preprocessor. – littleadv Jan 10 '22 at 06:03
I am so sorry, you're absolutely right. I meant the preprocessor. – afp_2008 Jan 10 '22 at 06:04
1

So preprocessor directives have to be on their own lines, you can't have two different directives on the same line. – littleadv Jan 10 '22 at 06:05

C++ Macro containing #ifdef

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