stdio/ungetc.c

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