C arg stuff

gistfile1.c

#include <stdio.h>
#include <string.h>
#include <stdarg.h>

#ifndef __COUNTER__
#error "Your C compiler doesn't support __COUNTER__. Try GCC >= 4.3 or Clang"
#endif

#define __GENSYM2(x,y) x ## y
#define __GENSYM1(x,y) __GENSYM2(x,y)
#define __GENSYM(x) __GENSYM1(x ## __gensym__, __COUNTER__)

#define __extract__2(ary, last, atype_t, args, ary_c, args_c) \
  atype_t *ary_c;                                  \
  atype_t args_c;                                  \
  va_list args;                                    \
  va_start(args, last);                            \
  ary_c = ary;                                     \
  while ((args_c = va_arg(args, atype_t)))         \
    *ary_c++ = args_c;                             \
  *ary_c = NULL;                                   \
  va_end(args)

#define __extract(ary, last, atype_t) \
  __extract__2(ary, last, atype_t, __GENSYM(args), __GENSYM(ary_c), __GENSYM(args_c))

char * join_ary(char * dest, char * sep, char ** ary) {
  char ** s = ary;  
  while (*s) {
    strcat(dest, *s);
    if (*++s) strcat(dest, sep);
  }
  return dest;
}

char * join_args(char * dest, char * sep, ...) {
  char *ary[128];
  __extract(ary, sep, char*);
  
  return join_ary(dest, sep, ary);
}

char * jstrcat(char * dest, ...) {
  char *ary[128];
  __extract(ary, dest, char*);
  return join_ary(dest, "", ary);
}

int main(int argc, char * argv[]) {

  if (argc < 2) {
    fprintf(stderr, "NEEDS ARG!\n");
    return 1;
  }

  char buf[512] = { '\0' };
  char *ary[] = { "First", "Second", "Third", NULL };

  join_ary(buf, argv[1], ary);
  printf("join_ary:  %s\n", buf);
  buf[0] = '\0';
  join_args(buf, argv[1], "Hitotsu", "Futatsu", "Mittsu", NULL);
  printf("join_args: %s\n", buf);
  buf[0] = '\0';
  jstrcat(buf, "foo", "bar", "baz", NULL);
  printf("jstrcat:   %s\n", buf);

  return 0;
}