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ungetc.c revision 1.1 
      1 /*-
      2  * Copyright (c) 1990 The Regents of the University of California.
      3  * 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. All advertising materials mentioning features or use of this software
     17  *    must display the following acknowledgement:
     18  *	This product includes software developed by the University of
     19  *	California, Berkeley and its contributors.
     20  * 4. Neither the name of the University nor the names of its contributors
     21  *    may be used to endorse or promote products derived from this software
     22  *    without specific prior written permission.
     23  *
     24  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     25  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     26  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     27  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     28  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     29  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     30  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     31  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     32  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     33  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     34  * SUCH DAMAGE.
     35  */
     36 
     37 #if defined(LIBC_SCCS) && !defined(lint)
     38 static char sccsid[] = "@(#)ungetc.c	5.6 (Berkeley) 5/4/91";
     39 #endif /* LIBC_SCCS and not lint */
     40 
     41 #include <stdio.h>
     42 #include <stdlib.h>
     43 #include <string.h>
     44 #include "local.h"
     45 
     46 /*
     47  * Expand the ungetc buffer `in place'.  That is, adjust fp->_p when
     48  * the buffer moves, so that it points the same distance from the end,
     49  * and move the bytes in the buffer around as necessary so that they
     50  * are all at the end (stack-style).
     51  */
     52 static
     53 __submore(fp)
     54 	register FILE *fp;
     55 {
     56 	register int i;
     57 	register unsigned char *p;
     58 
     59 	if (fp->_ub._base == fp->_ubuf) {
     60 		/*
     61 		 * Get a new buffer (rather than expanding the old one).
     62 		 */
     63 		if ((p = malloc((size_t)BUFSIZ)) == NULL)
     64 			return (EOF);
     65 		fp->_ub._base = p;
     66 		fp->_ub._size = BUFSIZ;
     67 		p += BUFSIZ - sizeof(fp->_ubuf);
     68 		for (i = sizeof(fp->_ubuf); --i >= 0;)
     69 			p[i] = fp->_ubuf[i];
     70 		fp->_p = p;
     71 		return (0);
     72 	}
     73 	i = fp->_ub._size;
     74 	p = realloc(fp->_ub._base, i << 1);
     75 	if (p == NULL)
     76 		return (EOF);
     77 	(void) bcopy((void *)p, (void *)(p + i), (size_t)i);
     78 	fp->_p = p + i;
     79 	fp->_ub._base = p;
     80 	fp->_ub._size = i << 1;
     81 	return (0);
     82 }
     83 
     84 ungetc(c, fp)
     85 	int c;
     86 	register FILE *fp;
     87 {
     88 	if (c == EOF)
     89 		return (EOF);
     90 	if (!__sdidinit)
     91 		__sinit();
     92 	if ((fp->_flags & __SRD) == 0) {
     93 		/*
     94 		 * Not already reading: no good unless reading-and-writing.
     95 		 * Otherwise, flush any current write stuff.
     96 		 */
     97 		if ((fp->_flags & __SRW) == 0)
     98 			return (EOF);
     99 		if (fp->_flags & __SWR) {
    100 			if (__sflush(fp))
    101 				return (EOF);
    102 			fp->_flags &= ~__SWR;
    103 			fp->_w = 0;
    104 			fp->_lbfsize = 0;
    105 		}
    106 		fp->_flags |= __SRD;
    107 	}
    108 	c = (unsigned char)c;
    109 
    110 	/*
    111 	 * If we are in the middle of ungetc'ing, just continue.
    112 	 * This may require expanding the current ungetc buffer.
    113 	 */
    114 	if (HASUB(fp)) {
    115 		if (fp->_r >= fp->_ub._size && __submore(fp))
    116 			return (EOF);
    117 		*--fp->_p = c;
    118 		fp->_r++;
    119 		return (c);
    120 	}
    121 
    122 	/*
    123 	 * If we can handle this by simply backing up, do so,
    124 	 * but never replace the original character.
    125 	 * (This makes sscanf() work when scanning `const' data.)
    126 	 */
    127 	if (fp->_bf._base != NULL && fp->_p > fp->_bf._base &&
    128 	    fp->_p[-1] == c) {
    129 		fp->_p--;
    130 		fp->_r++;
    131 		return (c);
    132 	}
    133 
    134 	/*
    135 	 * Create an ungetc buffer.
    136 	 * Initially, we will use the `reserve' buffer.
    137 	 */
    138 	fp->_ur = fp->_r;
    139 	fp->_up = fp->_p;
    140 	fp->_ub._base = fp->_ubuf;
    141 	fp->_ub._size = sizeof(fp->_ubuf);
    142 	fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
    143 	fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];
    144 	fp->_r = 1;
    145 	return (c);
    146 }
    147