xref: /netbsd/lib/libc/stdio/fgets.c (revision bf9ec67e)
1 /*	$NetBSD: fgets.c,v 1.14 2001/12/07 11:47:41 yamt 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[] = "@(#)fgets.c	8.2 (Berkeley) 12/22/93";
43 #else
44 __RCSID("$NetBSD: fgets.c,v 1.14 2001/12/07 11:47:41 yamt Exp $");
45 #endif
46 #endif /* LIBC_SCCS and not lint */
47 
48 #include <assert.h>
49 #include <stdio.h>
50 #include <string.h>
51 #include "local.h"
52 #include "reentrant.h"
53 
54 /*
55  * Read at most n-1 characters from the given file.
56  * Stop when a newline has been read, or the count runs out.
57  * Return first argument, or NULL if no characters were read.
58  */
59 char *
60 fgets(buf, n, fp)
61 	char *buf;
62 	int n;
63 	FILE *fp;
64 {
65 	int len;
66 	char *s;
67 	unsigned char *p, *t;
68 
69 	_DIAGASSERT(buf != NULL);
70 	_DIAGASSERT(fp != NULL);
71 	if (n <= 0)					/* sanity check */
72 		return (NULL);
73 
74 	FLOCKFILE(fp);
75 	_SET_ORIENTATION(fp, -1);
76 	s = buf;
77 	n--;			/* leave space for NUL */
78 	while (n != 0) {
79 		/*
80 		 * If the buffer is empty, refill it.
81 		 */
82 		if ((len = fp->_r) <= 0) {
83 			if (__srefill(fp)) {
84 				/* EOF/error: stop with partial or no line */
85 				if (s == buf) {
86 					FUNLOCKFILE(fp);
87 					return (NULL);
88 				}
89 				break;
90 			}
91 			len = fp->_r;
92 		}
93 		p = fp->_p;
94 
95 		/*
96 		 * Scan through at most n bytes of the current buffer,
97 		 * looking for '\n'.  If found, copy up to and including
98 		 * newline, and stop.  Otherwise, copy entire chunk
99 		 * and loop.
100 		 */
101 		if (len > n)
102 			len = n;
103 		t = memchr((void *)p, '\n', (size_t)len);
104 		if (t != NULL) {
105 			len = ++t - p;
106 			fp->_r -= len;
107 			fp->_p = t;
108 			(void)memcpy((void *)s, (void *)p, (size_t)len);
109 			s[len] = 0;
110 			FUNLOCKFILE(fp);
111 			return (buf);
112 		}
113 		fp->_r -= len;
114 		fp->_p += len;
115 		(void)memcpy((void *)s, (void *)p, (size_t)len);
116 		s += len;
117 		n -= len;
118 	}
119 	*s = 0;
120 	FUNLOCKFILE(fp);
121 	return (buf);
122 }
123