miss-1.c

this is a gcc file, you can download it and learn its usetility, for further detail please look at t

/* Test for warnings for missing format attributes.  */
/* Origin: Joseph Myers <[e-mail]> */
/* { dg-do compile } */
/* { dg-options "-std=gnu99 -Wformat -Wmissing-format-attribute" } */

#include "format.h"

void
foo (const char *fmt, ...)
{
  va_list ap;
  va_start (ap, fmt);
  vprintf (fmt, ap); /* { dg-warning "candidate" "printf attribute warning" } */
  va_end (ap);
}

void
bar (const char *fmt, ...)
{
  va_list ap;
  va_start (ap, fmt);
  vscanf (fmt, ap); /* { dg-warning "candidate" "scanf attribute warning" } */
  va_end (ap);
}

__attribute__((__format__(__printf__, 1, 2))) void
foo2 (const char *fmt, ...)
{
  va_list ap;
  va_start (ap, fmt);
  vprintf (fmt, ap);
  va_end (ap);
}

void
vfoo (const char *fmt, va_list arg)
{
  vprintf (fmt, arg); /* { dg-warning "candidate" "printf attribute warning 2" } */
}