glibc/stdio/vsnprintf.c

/* Copyright (C) 1991, 1992 Free Software Foundation, Inc.
This file is part of the GNU C Library.

The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version.

The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
Library General Public License for more details.

You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB.  If
not, write to the Free Software Foundation, Inc., 675 Mass Ave,
Cambridge, MA 02139, USA.  */

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


/*
 * Write formatted output to S according to the format string
 * FORMAT, using the argument list in ARG, writing no more
 * than MAXLEN characters.
 */
int
DEFUN(vsnprintf, (s, maxlen, format, arg),
	char *s AND size_t maxlen AND CONST char *format AND va_list arg)
{
  int done;
  FILE f;

  memset((PTR) &f, 0, sizeof(f));
  f.__magic = _IOMAGIC;
  f.__mode.__write = 1;
  /* The buffer size is one less than MAXLEN
     so we have space for the null terminator.  */
  f.__bufp = f.__buffer = (char *) s;
  f.__bufsize = maxlen - 1;
  f.__put_limit = f.__buffer + f.__bufsize;
  f.__get_limit = f.__buffer;
  /* After the buffer is full (MAXLEN characters have been written),
     any more characters written will go to the bit bucket.  */
  f.__room_funcs = __default_room_functions;
  f.__io_funcs.__write = NULL;
  f.__seen = 1;

  done = vfprintf(&f, format, arg);
  *f.__bufp = '\0';

  return done;
}