sysdeps/posix/stdio_init.c

   1 /* Copyright (C) 1991, 1992, 1993, 1995 Free Software Foundation, Inc.
   2 This file is part of the GNU C Library.
   3
   4 The GNU C Library is free software; you can redistribute it and/or
   5 modify it under the terms of the GNU Library General Public License as
   6 published by the Free Software Foundation; either version 2 of the
   7 License, or (at your option) any later version.
   8
   9 The GNU C Library is distributed in the hope that it will be useful,
  10 but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12 Library General Public License for more details.
  13
  14 You should have received a copy of the GNU Library General Public
  15 License along with the GNU C Library; see the file COPYING.LIB.  If
  16 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  17 Cambridge, MA 02139, USA.  */
  18
  19 #include <ansidecl.h>
  20 #include <stdio.h>
  21 #include <sys/types.h>
  22 #include <sys/stat.h>
  23 #include <unistd.h>
  24
  25 /* Initialize STREAM as necessary.
  26    This may change I/O functions, give a buffer, etc.
  27    If no buffer is allocated, but the bufsize is set,
  28    the bufsize will be used to allocate the buffer.  */
  29 void
  30 DEFUN(__stdio_init_stream, (stream), FILE *stream)
  31 {
  32   register CONST int fd = (int) stream->__cookie;
  33   struct stat statb;
  34
  35   if (stream->__buffer != NULL || stream->__userbuf)
  36     /* If's unbuffered by request, we can't do anything useful.  */
  37     return;
  38
  39   /* Find out what sort of file this is.  */
  40   if (__fstat (fd, &statb) < 0)
  41       return;
  42
  43   if (S_ISCHR (statb.st_mode))
  44     {
  45       /* It's a character device.
  46          Make it line-buffered if it's a terminal.  */
  47       if (__isatty (fd))
  48         {
  49           stream->__linebuf = 1;
  50
  51           /* Unix terminal devices have the bad habit of claiming to be
  52              seekable.  On systems I have tried, seeking on a terminal
  53              device seems to set its file position as specified, such that
  54              a later tell says the same thing.  This is in no way related
  55              to actual seekability--the ability to seek back and read old
  56              data.  Unix terminal devices will let you "seek back", and
  57              then read more new data from the terminal.  I can think of
  58              nothing to do about this lossage except to preemptively disable
  59              seeking on terminal devices.  */
  60
  61           stream->__io_funcs.__seek = NULL; /* Seeks get ESPIPE.  */
  62         }
  63     }
  64
  65 #ifdef  _STATBUF_ST_BLKSIZE
  66   /* Use the block-size field to determine
  67      the system's optimal buffering size.  */
  68   stream->__bufsize = statb.st_blksize;
  69 #endif
  70 }