Question

For example: If I have two .h files

process1.h and process2.h

and they contain two function with different output variables.

process1.h:

function(int var)
 {
 return 2*var;
}

process2.h:

function(int var)
 {
 return 10*var;
}

Can this be done in main.c:

int main()
{
int a = 2;
#include "process1.h"
printf("%d",function(a));    //output is 4

EXCLUDE #INCLUDE "process1.h" ?????    <----can this be done in any way??
#include "process2.h"
printf("%d",function(a));    //output is 20

}

Answer 1

No, you cannot “un-include” a file. Think of all the preprocessor directives (lines starting with #) as happening before the actual C compiler even sees the source file. They just operate on the text of the file, and the preprocessor could be implemented as a separate step that just feeds new text into the actual compiler.

The best way to modify the actions of an include depending on the caller is to use further macros inside the included files, that you can #define before including them.

Still, your overall syntax is off, you can’t (typically) nest functions in C.