Home | History | Annotate | Line # | Download | only in stdio
ungetc.c revision 1.7 
      1 /*	$NetBSD: ungetc.c,v 1.7 1998/02/03 18:41:22 perry Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 1990, 1993
      5  *	The Regents of the University of California.  All rights reserved.
      6  *
      7  * This code is derived from software contributed to Berkeley by
      8  * Chris Torek.
      9  *
     10  * Redistribution and use in source and binary forms, with or without
     11  * modification, are permitted provided that the following conditions
     12  * are met:
     13  * 1. Redistributions of source code must retain the above copyright
     14  *    notice, this list of conditions and the following disclaimer.
     15  * 2. Redistributions in binary form must reproduce the above copyright
     16  *    notice, this list of conditions and the following disclaimer in the
     17  *    documentation and/or other materials provided with the distribution.
     18  * 3. All advertising materials mentioning features or use of this software
     19  *    must display the following acknowledgement:
     20  *	This product includes software developed by the University of
     21  *	California, Berkeley and its contributors.
     22  * 4. Neither the name of the University nor the names of its contributors
     23  *    may be used to endorse or promote products derived from this software
     24  *    without specific prior written permission.
     25  *
     26  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     27  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     28  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     29  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     30  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     31  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     32  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     33  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     34  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     35  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     36  * SUCH DAMAGE.
     37  */
     38 
     39 #include <sys/cdefs.h>
     40 #if defined(LIBC_SCCS) && !defined(lint)
     41 #if 0
     42 static char sccsid[] = "@(#)ungetc.c	8.2 (Berkeley) 11/3/93";
     43 #else
     44 __RCSID("$NetBSD: ungetc.c,v 1.7 1998/02/03 18:41:22 perry Exp $");
     45 #endif
     46 #endif /* LIBC_SCCS and not lint */
     47 
     48 #include <stdio.h>
     49 #include <stdlib.h>
     50 #include <string.h>
     51 #include "local.h"
     52 
     53 static int __submore __P((FILE *));
     54 /*
     55  * Expand the ungetc buffer `in place'.  That is, adjust fp->_p when
     56  * the buffer moves, so that it points the same distance from the end,
     57  * and move the bytes in the buffer around as necessary so that they
     58  * are all at the end (stack-style).
     59  */
     60 static int
     61 __submore(fp)
     62 	FILE *fp;
     63 {
     64 	int i;
     65 	unsigned char *p;
     66 
     67 	if (fp->_ub._base == fp->_ubuf) {
     68 		/*
     69 		 * Get a new buffer (rather than expanding the old one).
     70 		 */
     71 		if ((p = malloc((size_t)BUFSIZ)) == NULL)
     72 			return (EOF);
     73 		fp->_ub._base = p;
     74 		fp->_ub._size = BUFSIZ;
     75 		p += BUFSIZ - sizeof(fp->_ubuf);
     76 		for (i = sizeof(fp->_ubuf); --i >= 0;)
     77 			p[i] = fp->_ubuf[i];
     78 		fp->_p = p;
     79 		return (0);
     80 	}
     81 	i = fp->_ub._size;
     82 	p = realloc(fp->_ub._base, i << 1);
     83 	if (p == NULL)
     84 		return (EOF);
     85 	/* no overlap (hence can use memcpy) because we doubled the size */
     86 	(void)memcpy((void *)(p + i), (void *)p, (size_t)i);
     87 	fp->_p = p + i;
     88 	fp->_ub._base = p;
     89 	fp->_ub._size = i << 1;
     90 	return (0);
     91 }
     92 
     93 int
     94 ungetc(c, fp)
     95 	int c;
     96 	FILE *fp;
     97 {
     98 	if (c == EOF)
     99 		return (EOF);
    100 	if (!__sdidinit)
    101 		__sinit();
    102 	if ((fp->_flags & __SRD) == 0) {
    103 		/*
    104 		 * Not already reading: no good unless reading-and-writing.
    105 		 * Otherwise, flush any current write stuff.
    106 		 */
    107 		if ((fp->_flags & __SRW) == 0)
    108 			return (EOF);
    109 		if (fp->_flags & __SWR) {
    110 			if (__sflush(fp))
    111 				return (EOF);
    112 			fp->_flags &= ~__SWR;
    113 			fp->_w = 0;
    114 			fp->_lbfsize = 0;
    115 		}
    116 		fp->_flags |= __SRD;
    117 	}
    118 	c = (unsigned char)c;
    119 
    120 	/*
    121 	 * If we are in the middle of ungetc'ing, just continue.
    122 	 * This may require expanding the current ungetc buffer.
    123 	 */
    124 	if (HASUB(fp)) {
    125 		if (fp->_r >= fp->_ub._size && __submore(fp))
    126 			return (EOF);
    127 		*--fp->_p = c;
    128 		fp->_r++;
    129 		return (c);
    130 	}
    131 	fp->_flags &= ~__SEOF;
    132 
    133 	/*
    134 	 * If we can handle this by simply backing up, do so,
    135 	 * but never replace the original character.
    136 	 * (This makes sscanf() work when scanning `const' data.)
    137 	 */
    138 	if (fp->_bf._base != NULL && fp->_p > fp->_bf._base &&
    139 	    fp->_p[-1] == c) {
    140 		fp->_p--;
    141 		fp->_r++;
    142 		return (c);
    143 	}
    144 
    145 	/*
    146 	 * Create an ungetc buffer.
    147 	 * Initially, we will use the `reserve' buffer.
    148 	 */
    149 	fp->_ur = fp->_r;
    150 	fp->_up = fp->_p;
    151 	fp->_ub._base = fp->_ubuf;
    152 	fp->_ub._size = sizeof(fp->_ubuf);
    153 	fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
    154 	fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];
    155 	fp->_r = 1;
    156 	return (c);
    157 }
    158