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#define not working

Started by CodeZero Dec 7, 2011 at 11:45 PM 2 replies 1.1k views

Original Post

Dec 7, 2011 at 11:45 PM

I have 3 files:

main.cpp


 #define TESTING123
 #include "other.h"
 
 int main ( ) {
 
 x++;
 
 return 0;
 }

other.h


 #ifndef OTHER_H
 #define OTHER_H
 
 #ifdef TESTING123
 extern int x;
 #endif
 
 #endif

other.cpp


 
 #include "other.h"
 
 #ifdef TESTING123
 int x= 0;
 #endif

I get a linker error for x being unresolved. Why?

Thanks,
Jake

Dec 7, 2011 at 11:48 PM

"TESTING123" is not defined in other.cpp or any header included by it.

Dec 8, 2011 at 12:01 AM

#include just means "copy and paste this file here", so if you do the C&P manually, you get:
main.cpp

#define TESTING123
 #ifndef OTHER_H
 # define OTHER_H
 # ifdef TESTING123
 extern int x;
 # endif
 #endif
 int main ( ) {
 x++;
 return 0;
 }

other.cpp

#ifndef OTHER_H
 # define OTHER_H
 # ifdef TESTING123
 extern int x;
 # endif
 #endif
 #ifdef TESTING123
 int x= 0;
 #endif

And if you then resolve the #if conditions manually, you get:
main.cpp

extern int x;
 int main ( ) {
 x++;
 return 0;
 }

other.cpp

Dec 8, 2011 at 10:46 AM

Typically such a situation would be handled by setting up the #define across the whole project, e.g. in your toolchain/project settings.

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