引用:

---

      gets()  and fgets() return s on success, and NULL on error or when end of file occurs while no characters have been read.

---

代码:

---

/* Copyright (C) 1991, 92, 95, 96, 97, 98 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Library General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  If not,
   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

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

/* Reads characters from STREAM into S, until either a newline character
   is read, N - 1 characters have been read, or EOF is seen.  Returns
   the newline, unlike gets.  Finishes by appending a null character and
   returning S.  If EOF is seen before any characters have been written
   to S, the function returns NULL without appending the null character.
   If there is a file error, always return NULL.  */
char *
fgets (s, n, stream)
     char *s;
     int n;
     FILE *stream;
{
	register char *p = s;
	
	if (!__validfp (stream) || s == NULL || n <= 0)
	{
		__set_errno (EINVAL);
		return NULL;
	}
	
	if (ferror (stream))
		return NULL;
	
	if (stream->__buffer == NULL && stream->__userbuf)
	{
		/* Unbuffered stream.  Not much optimization to do.  */
		register int c = 0;
		while (--n > 0 && (c = getc (stream)) != EOF)
			if ((*p++ = c) == '\n')
				break;
		if (c == EOF && (p == s || ferror (stream)))
			return NULL;
		*p = '\0';
		return s;
	}
	
	/* Leave space for the null.  */
	--n;
	
	if (n > 0 &&
	(!stream->__seen || stream->__buffer == NULL || stream->__pushed_back))
	{
		/* Do one with getc to allocate a buffer.  */
		int c = getc (stream);
		if (c == EOF)
			return NULL;
		*p++ = c;
		if (c == '\n')
		{
			*p = '\0';
			return s;
		}
		else
			--n;
	}
	
	while (n > 0)
	{
		size_t i;
		char *found;
		
		i = stream->__get_limit - stream->__bufp;
		if (i == 0)
		{
			/* Refill the buffer.  */
			int c = __fillbf (stream);
			if (c == EOF)
			break;
			*p++ = c;
			--n;
			if (c == '\n')
			{
				*p = '\0';
				return s;
			}
			i = stream->__get_limit - stream->__bufp;
		}
		
		if (i > (size_t) n)
			i = n;
		
		found = (char *) __memccpy ((void *) p, stream->__bufp, '\n', i);
		
		if (found != NULL)
		{
			stream->__bufp += found - p;
			p = found;
			break;
		}
		
		stream->__bufp += i;
		n -= i;
		p += i;
	}
	
	if (p == s)
		return NULL;
	
	*p = '\0';
	return ferror (stream) ? NULL : s;
}

weak_alias (fgets, fgets_unlocked)

---

代码:

---

char *p = (char*) malloc(3);
memcpy(p,"abcd",4);
if(p)
  free(p);

---

引用:

---

回复人： Kert_t8() ( ) 信誉：100  2005-1-31 13:26:36  得分: 0 


 
由于成功的时候就会返回s，所以我一直使用的是
s=fgets(s, size, FileStream);

但是如果照楼上说得那样，我就需要重新声明一个变量，似乎觉得有点不爽。
你们做的程序都是用的: v1=fgets(v2, size, FileStream) 吗？

我没用过c，所以....

---

代码:

---

if(NULL == fget(s,n,stream))
 return;//这里不用想s肯定是空的
else
 printf("%s\n",s);//不用判断也知道s成功取回

---