CFG_START()
CFG_ADD(int, FOO, /* some more stuff */)
CFG_ADD(short, BAR, /* some more stuff */)
CFG_ADD(float, BAZ, /* some more stuff */)
CFG_END()

##</code><code>##

/* simplified */
MetaData_t metadata = {
    #define CFG_ADD(TYPE,NAME,STUFF) { .compFunc = compare_ ## TYPE; /* and some more stuff */ }
    #include "configfile.h"
    #undef CFG_ADD
}

##</code><code>##

#define CFG_ADD(TYPE,NAME,STUFF) \
    #ifndef USING_ ## TYPE /* does not work */ \
    #define USING_ ## TYPE /* does not work */ \
    #endif
#include "configfile.h"
#undef CFG_ADD

/* and later: */

#ifdef USING_int
static int compare_int(const void * a, const void * b);
#endif
#ifdef USING_double
static int compare_double(const void * a, const void * b);
#endif

/* further down */

#ifdef USING_int
static int compare_int(const void * a, const void * b)
{
    /* ... */
}
#endif

#ifdef USING_double
static int compare_double(const void * a, const void * b)
{
    /* ... */
}
#endif