glibc/sysdeps/posix/stdio_init.c

/* Copyright (C) 1991, 1992, 1993, 1995, 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 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., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>

/* Initialize STREAM as necessary.
   This may change I/O functions, give a buffer, etc.
   If no buffer is allocated, but the bufsize is set,
   the bufsize will be used to allocate the buffer.  */
void
__stdio_init_stream (FILE *stream)
{
  const int fd = (int) stream->__cookie;
  struct stat statb;

  if (stream->__buffer != NULL || stream->__userbuf)
    /* If's unbuffered by request, we can't do anything useful.  */
    return;

  /* Find out what sort of file this is.  */
  if (__fstat (fd, &statb) < 0)
      return;

  if (S_ISCHR (statb.st_mode))
    {
      /* It's a character device.
	 Make it line-buffered if it's a terminal.  */
      if (__isatty (fd))
	{
	  stream->__linebuf = 1;

	  /* Unix terminal devices have the bad habit of claiming to be
	     seekable.  On systems I have tried, seeking on a terminal
	     device seems to set its file position as specified, such that
	     a later tell says the same thing.  This is in no way related
	     to actual seekability--the ability to seek back and read old
	     data.  Unix terminal devices will let you "seek back", and
	     then read more new data from the terminal.  I can think of
	     nothing to do about this lossage except to preemptively disable
	     seeking on terminal devices.  */

	  stream->__io_funcs.__seek = NULL; /* Seeks get ESPIPE.  */
	}
    }

#ifdef	_STATBUF_ST_BLKSIZE
  /* Use the block-size field to determine
     the system's optimal buffering size.  */
  stream->__bufsize = statb.st_blksize;
#endif
}