stdio.c

#include <stdio.h>
#include <ctype.h>
#include <inttypes.h>
#include <round.h>
#include <stdint.h>
#include <string.h>

/* Auxiliary data for vsnprintf_helper(). */
struct vsnprintf_aux 
  {
    char *p;            /* Current output position. */
    int length;         /* Length of output string. */
    int max_length;     /* Max length of output string. */
  };

static void vsnprintf_helper (char, void *);

/* Like vprintf(), except that output is stored into BUFFER,
   which must have space for BUF_SIZE characters.  Writes at most
   BUF_SIZE - 1 characters to BUFFER, followed by a null
   terminator.  BUFFER will always be null-terminated unless
   BUF_SIZE is zero.  Returns the number of characters that would
   have been written to BUFFER, not including a null terminator,
   had there been enough room. */
int
vsnprintf (char *buffer, size_t buf_size, const char *format, va_list args) 
{
  /* Set up aux data for vsnprintf_helper(). */
  struct vsnprintf_aux aux;
  aux.p = buffer;
  aux.length = 0;
  aux.max_length = buf_size > 0 ? buf_size - 1 : 0;

  /* Do most of the work. */
  __vprintf (format, args, vsnprintf_helper, &aux);

  /* Add null terminator. */
  if (buf_size > 0)
    *aux.p = '\0';

  return aux.length;
}

/* Helper function for vsnprintf(). */
static void
vsnprintf_helper (char ch, void *aux_)
{
  struct vsnprintf_aux *aux = aux_;

  if (aux->length++ < aux->max_length)
    *aux->p++ = ch;
}

/* Like printf(), except that output is stored into BUFFER,
   which must have space for BUF_SIZE characters.  Writes at most
   BUF_SIZE - 1 characters to BUFFER, followed by a null
   terminator.  BUFFER will always be null-terminated unless
   BUF_SIZE is zero.  Returns the number of characters that would
   have been written to BUFFER, not including a null terminator,
   had there been enough room. */
int
snprintf (char *buffer, size_t buf_size, const char *format, ...) 
{
  va_list args;
  int retval;

  va_start (args, format);
  retval = vsnprintf (buffer, buf_size, format, args);
  va_end (args);