xref: /src/lib/libc/stdio/fgets.c

/*-
 * Copyright (c) 1990 The Regents of the University of California.
 * All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Chris Torek.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)fgets.c	5.4 (Berkeley) 5/4/91";
#endif /* LIBC_SCCS and not lint */

#include <stdio.h>
#include <string.h>

/*
 * Read at most n-1 characters from the given file.
 * Stop when a newline has been read, or the count runs out.
 * Return first argument, or NULL if no characters were read.
 */
char *
fgets(buf, n, fp)
	char *buf;
	register size_t n;
	register FILE *fp;
{
	register size_t len;
	register char *s;
	register unsigned char *p, *t;

	if (n < 2)		/* sanity check */
		return (NULL);

	s = buf;
	n--;			/* leave space for NUL */
	do {
		/*
		 * If the buffer is empty, refill it.
		 */
		if ((len = fp->_r) <= 0) {
			if (__srefill(fp)) {
				/* EOF/error: stop with partial or no line */
				if (s == buf)
					return (NULL);
				break;
			}
			len = fp->_r;
		}
		p = fp->_p;

		/*
		 * Scan through at most n bytes of the current buffer,
		 * looking for '\n'.  If found, copy up to and including
		 * newline, and stop.  Otherwise, copy entire chunk
		 * and loop.
		 */
		if (len > n)
			len = n;
		t = memchr((void *)p, '\n', len);
		if (t != NULL) {
			len = ++t - p;
			fp->_r -= len;
			fp->_p = t;
			(void) bcopy((void *)p, (void *)s, len);
			s[len] = 0;
			return (buf);
		}
		fp->_r -= len;
		fp->_p += len;
		(void) bcopy((void *)p, (void *)s, len);
		s += len;
	} while ((n -= len) != 0);
	*s = 0;
	return (buf);
}