Question

That may be really simple but I’m unable to find a good answer.
How can I make a macro representing first a certain value and then a different one?

I know that’s nasty but I need it to implicitly declare a variable the first time and then do nothing.
This variable is required by other macros that I’m implementing.

Should I leverage “argument prescan”?

The thing you need to know is the fact I’m generating the code:

#define INC_X x++ //should be declared if needed to
#define PRINT_X printf("VALUE OF X: %d\n", x)

int func() {
[...]
INC_X;
[...]
INC_X;
[...]
PRINT_X;
[...]
}

Answer 1

As far as I know, this is impossible. I know of no way for the expansion of a macro to control the way another macro — or itself — will be expanded after. C99 introduced _Pragma so that #pragma things can be done in macros, but there is no equivalent for #define or #undef.