Defining and undefining #defines from command line

[John (Eljay) Love-Jensen]

Hi José,

The -UAGE will not undefine #define's in your source code.

The -UAGE will undefine predefines by GCC.  (Or undefine -DAGE that occurred earlier in the command line.)

This is what you are trying to do:

#include<stdio.h>
#ifndef AGE
#define AGE 29
#endif
int main()
{
  printf("Hello, I'm %d years old\n",AGE);
  return 0;
}

gcc -DAGE=30 hello.c -o hello

HTH,
--Eljay