Given this:

#define NUM 100

I was to use a CPP macro like:

char *p = MACRO(NUM);

and have MACRO defined such that it would expand to:

char *p = "100";

I tried:

#define MACRO(X) #X

but, for MACRO(NUM), that expands to:

char *p = "NUM";

How can I get CPP to expand NUM first?

- Paul

On May 9, 10:26pm, "Paul J. Lucas" <paul-nos...@nospam.lucasmail.org>
wrote:
> Given this:
>
> #define NUM 100
>
> I was to use a CPP macro like:
>
> char *p = MACRO(NUM);
>
> and have MACRO defined such that it would expand to:
>
> char *p = "100";
>
> I tried:
>
> #define MACRO(X) #X
>
> but, for MACRO(NUM), that expands to:
>
> char *p = "NUM";
>
> How can I get CPP to expand NUM first?
>
> - Paul

The preprocessor will expand the macro parameters first, unless
they appear next to a # (or ##).
So try this:

#define NUM 100
#define MACRO(X) #X
#define GOODMACRO(X) MACRO(X)

char *p=GOODMACRO(NUM);

GOODMACRO's argument is not following an #, so it is expanded, prior
to
looking at MACRO's meaning.

Szabolcs

On May 10, 12:26 am, "Paul J. Lucas" <paul-
nos...@nospam.lucasmail.org> wrote:
> Given this:
>
> #define NUM 100
>
> I was to use a CPP macro like:
>
> char *p = MACRO(NUM);
>
> and have MACRO defined such that it would expand to:
>
> char *p = "100";
>
> I tried:
>
> #define MACRO(X) #X
>
> but, for MACRO(NUM), that expands to:
>
> char *p = "NUM";
>
Question 11.17 of the C-faq.
<http://c-faq.com/>