stdio/ungetc.c

   1 /* Copyright (C) 1991, 1993, 1996 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 <errno.h>
  20 #include <stdio.h>
  21
  22
  23 /* Push the character C back onto the input stream of STREAM.  */
  24 int
  25 ungetc (c, stream)
  26      register int c;
  27      register FILE *stream;
  28 {
  29   if (!__validfp (stream) || !stream->__mode.__read)
  30     {
  31       __set_errno (EINVAL);
  32       return EOF;
  33     }
  34
  35   if (c == EOF)
  36     return EOF;
  37
  38   if (stream->__pushed_back)
  39     /* There is already a char pushed back.  */
  40     return EOF;
  41
  42   if ((stream->__linebuf_active || stream->__put_limit > stream->__buffer) &&
  43       /* This is a read-write stream with something in its buffer.
  44          Flush the stream.  */
  45       __flshfp (stream, EOF) == EOF)
  46     return EOF;
  47
  48   stream->__pushback = (unsigned char) c;
  49   /* Tell __fillbf we've pushed back a char.  */
  50   stream->__pushed_back = 1;
  51   stream->__pushback_bufp = stream->__bufp;
  52   /* Make the next getc call __fillbf.  It will return C.  */
  53   stream->__bufp = stream->__get_limit;
  54
  55   /* We just gave it another character to read, so it's not at EOF.  */
  56   stream->__eof = 0;
  57
  58   return stream->__pushback;
  59 }