Greenspun's Tenth Rule


#include <stdio.h>
#include <stdlib.h>

void *apply(void *callee, int argc, void *argv) {
void **as = (void**)argv;
void *(*f)(void *a,...) = (void *(*)(void *a, ...))callee;

switch(argc) {
case 0: return ((void* (*)())f)();
case 1: return f(as[0]);
case 2: return f(as[0], as[1]);
case 3: return f(as[0], as[1], as[2]);
case 4: return f(as[0], as[1], as[2], as[3]);
default:
printf("apply: number of arguments limit reached\n");
abort();
}
}

int main(int argc, char **argv) {
char *as[] = {"hello %s\n" , "world"};
apply(printf, 2, as);
return 0;
}


>>12
POSIX requires that this be possible (e.g. for dlsym) even though DA STANDARD itself does not. So in practice you can assume this will work.