Using defined(MACRO) inside the C if statement

Question

I would like to write code in C something like this:

if(defined(MACRO))
  ...
else
  ...

but I could not find any way to do this in

Answer 1

Ok, based on the previous post I got this idea, which seems to work:

#define DEFINEDX(NAME) ((#NAME)[0] == 0)
#define DEFINED(NAME) DEFINEDX(NAME)

This will check if NAME is defined and therefore it expands to the empty string with 0 at its first character, or it is undefined in which case it is not the empty string. This works with GCC, so one can write

if( DEFINED(MACRO) )
  ...