variable datatype arguments in variadic functions

Can开发者_运维知识库 we pass arguments of different datatypes to same variadic function at the same time?

sure, look at common usages of printf:

printf("Error %d: %s", errNum, errTxt);

so ross$ expand < variadic.c && cc -Wall -Wextra variadic.c 
#include <stdio.h>
#include <stdarg.h>

void f(int, ...);
struct x { int a, b; } y = { 5, 6 };

int main(void) {
  float q = 9.4;
  f(0, 1.234, &q, "how now", 123, &y);
  return 0;
}

void f(int nothing, ...) {
  va_list ap;

  va_start(ap, nothing);
  double f = va_arg(ap, double);
  float *f2 = va_arg(ap, float *);
  char  *s   = va_arg(ap, char *);
  int    i    = va_arg(ap, int);
  struct x *sx = va_arg(ap, struct x *);
  va_end(ap);

  printf("%5.3f %3.1f %s %d %d/%d\n", f, *f2, s, i, sx->a, sx->b);
}
so ross$ ./a.out
1.234 9.4 how now 123 5/6

Here's a printf-free example ( old version: http://codepad.org/vnjFj7Uh )

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

/* return the maximum of n values. if n < 1 returns 0 */
/* lying to the compiler is not supported in this version, eg:         **
**    va_max(4, 8, 8, 8, 8, 8, 8, 8, 8)                                **
** or                                                                  **
**    va_max(4, 2, 2)                                                  **
/* is a bad way to call the function (and invokes Undefined Behaviour) */
int va_max(int n, ...) {
  int res;
  va_list arg;

  if (n < 1) return 0;

  va_start(arg, n);
  n--;
  res = va_arg(arg, int);
  while (n--) {
    int cur = va_arg(arg, int);
    if (cur > res) res = cur;
  }
  return res;
}

int main(void) {
  int test6 = va_max(6, 1, 2, 3, 4, 5, 6);
  int test3 = va_max(3, 56, 34, 12);
  if (test6 == 6) puts("6");
  if (test3 == 56) puts("56");
  return 0;
}

I made a function to unpack binary data using a varadic function,it takes different types based on what you want "encoded/decoded".

You'd use it like:

uint32_t a;
uint16_t b;
uint16_t c;
uint8_t *buf = ....;

depickle(buf,"sis",&a,&b,&c);

where 's' expects an uint16_t* and decodes 2 bytes from buf into a as little endian, 'i' says to decode 4 bytes as little endian into 'b'

Or to e.g. decode 4 bytes as big endian into a uint32_t:

uint32_t a;
uint8_t buf[] = {0x12,0x34,0x56,0x78};
depickle(buf,"I",&a);

There's still an early version around here.