glibc/stdio/fmemopen.c

/* Copyright (C) 1991, 1992, 1993, 1996, 1997 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 Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#include <errno.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>


/* Defined in fopen.c.  */
extern int __getmode __P ((const char *mode, __io_mode *mptr));

/* Open a new stream that will read and/or write from the buffer in
   S, which is of LEN bytes.  If the mode indicates appending, the
   buffer pointer is set to point to the first '\0' in the buffer.
   If S is NULL, the buffer is allocated by malloc and will be freed
   when the stream is closed.  The only purpose of this is to write
   things and then read what's been written.  If LEN is zero, writes will
   always return errors and reads will always return end-of-file.

   The stream is set up such that seeks and tells will always fail and
   once the buffer is full of written characters or empty of characters
   to read, attempted writes always return an output error and attempted
   reads always return end-of-file.  */
FILE *
fmemopen (s, len, mode)
     void *s;
     size_t len;
     const char *mode;
{
  __io_mode m;
  register FILE *stream;

  if (!__getmode (mode, &m))
    return NULL;

  stream = __newstream ();
  if (stream == NULL)
    return NULL;

  stream->__mode = m;

  /* Input gets EOF.  */
  stream->__room_funcs.__input = NULL;
  /* Output gets error.  */
  stream->__room_funcs.__output = NULL;

  /* Do nothing for close.  */
  stream->__io_funcs.__close = NULL;
  /* Can't seek outside the buffer.  */
  stream->__io_funcs.__seek = NULL;
  /* There is no associated file descriptor to fetch.  */
  stream->__io_funcs.__fileno = NULL;

  stream->__seen = 1;

  stream->__userbuf = s != NULL && len > 0;
  if (s == NULL)
    {
      s = malloc (len);
      if (s == NULL)
	{
	  int save = errno;
	  (void) fclose (stream);
	  __set_errno (save);
	  return NULL;
	}
    }

  stream->__buffer = (char *) s;
  stream->__bufsize = len;

  stream->__bufp = stream->__buffer;
  stream->__get_limit = (stream->__buffer +
			 (stream->__mode.__read ? stream->__bufsize : 0));
  stream->__put_limit = (stream->__buffer +
			 (stream->__mode.__write ? stream->__bufsize : 0));
  stream->__cookie = NULL;

  if (stream->__mode.__append)
    {
      char *p = memchr (stream->__bufp, '\0',
			stream->__get_limit - stream->__bufp);
      if (p == NULL)
	stream->__bufp = stream->__get_limit;
      else
	stream->__bufp = p;
    }
  else if (stream->__mode.__truncate)
    memset ((void *) stream->__buffer, 0, len);

  return stream;
}