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root/usr/lib/libc/stdio/ungetc.c

DEFINITIONS

1. ungetc

   1 /*-
   2  * Copyright (c) 1990, 1993
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * This code is derived from software contributed to Berkeley by
   6  * Chris Torek.
   7  *
   8  * Redistribution and use in source and binary forms, with or without
   9  * modification, are permitted provided that the following conditions
  10  * are met:
  11  * 1. Redistributions of source code must retain the above copyright
  12  *    notice, this list of conditions and the following disclaimer.
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in the
  15  *    documentation and/or other materials provided with the distribution.
  16  * 3. Neither the name of the University nor the names of its contributors
  17  *    may be used to endorse or promote products derived from this software
  18  *    without specific prior written permission.
  19  *
  20  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  30  * SUCH DAMAGE.
  31  */
  33 #include <stdio.h>
  34 #include <stdlib.h>
  35 #include <string.h>
  36 #include "local.h"
  38 int
ungetc(c, fp)
  40         int c;
FILE *fp;
  42 {
  43         if (c == EOF)
  44                 return (EOF);
  45         if (!__sdidinit)
__sinit();
  47         if ((fp->_flags & __SRD) == 0) {
  48                 /*
  49                  * Not already reading: no good unless reading-and-writing.
  50                  * Otherwise, flush any current write stuff.
  51                  */
  52                 if ((fp->_flags & __SRW) == 0)
  53                         return (EOF);
  54                 if (fp->_flags & __SWR) {
  55                         if (__sflush(fp))
  56                                 return (EOF);
fp->_flags &= ~__SWR;
fp->_w = 0;
  59                 }
fp->_flags |= __SRD;
  61         }
c = (unsigned char)c;
  64         /*
  65          * If we are in the middle of ungetc'ing, just continue.
  66          */
  67         if (HASUB(fp)) {
  68                 if (fp->_r >= fp->_ub._size)
  69                         return (EOF);
  70                 *--fp->_p = c;
fp->_r++;
  72                 return (c);
  73         }
fp->_flags &= ~__SEOF;
  76         /*
  77          * If we can handle this by simply backing up, do so,
  78          * but never replace the original character.
  79          * (This makes sscanf() work when scanning `const' data.)
  80          */
  81         if (fp->_bf._base != NULL && fp->_p > fp->_bf._base &&
fp->_p[-1] == c) {
fp->_p--;
fp->_r++;
  85                 return (c);
  86         }
  88         /*
  89          * Create an ungetc buffer.
  90          * we will use the `reserve' buffer.
  91          */
fp->_ur = fp->_r;
fp->_up = fp->_p;
fp->_ub._base = fp->_ubuf;
fp->_ub._size = sizeof(fp->_ubuf);
fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];
fp->_r = 1;
  99         return (c);
 100 }