In addition to define and include there are a
handful of other directives that may come in handy. The most useful
is probably the conditionals.
#ifdef SOMETHING
#else
#endif
#ifndef SOMETHING
#endif
The value in the conditional is either set up using a define
statement or can be set during compilation. Unfortunately conditionals
like this tend to require a recompilation to change the value.
Example:
#include <stdio.h>
#include <stdlib.h>
int main ( void ) {
int i = 5;
int j = i + 5;
/* The following will only execute if this program is compiled to set DEBUG
to something non-zero or if DEBUG is defined in a header */
#ifdef DEBUG
printf ( "i = %d\n", i );
#endif
printf ( "j = %d\n", j );
exit ( 0 );
}
If you want to set the DEBUG flag at compile time then you can do something
like this
cc -Wall -DDEBUG -o test test.c
