simple fgets source code

/*-
 * Copyright (c) 1990, 1993
 * 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.
 * 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 8.2 (Berkeley) 12/22/93";
#endif /* LIBC_SCCS and not lint */
#include <sys/cdefs.h>
__FBSDID("$FreeBSD: src/lib/libc/stdio/fgets.c,v 1.14 2007/01/09 00:28:06 imp Exp $");

#include "namespace.h"
#include <stdio.h>
#include <string.h>
#include "un-namespace.h"
#include "local.h"
#include "libc_private.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;
 int n;
 FILE *fp;
{
 size_t len;
 char *s;
 unsigned char *p, *t;

 if (n <= 0)  /* sanity check */
  return (NULL);

 FLOCKFILE(fp);
 ORIENT(fp, -1);
 s = buf;
 n--;   /* leave space for NUL */
 while (n != 0) {
  /*
   * 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) {
     FUNLOCKFILE(fp);
     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)memcpy((void *)s, (void *)p, len);
   s[len] = 0;
   FUNLOCKFILE(fp);
   return (buf);
  }
  fp->_r -= len;
  fp->_p += len;
  (void)memcpy((void *)s, (void *)p, len);
  s += len;
  n -= len;
 }
 *s = 0;
 FUNLOCKFILE(fp);
 return (buf);
}