关于库函数STRCMP的实现

[Double_Lan_2975]

我在C语言现代方法这本书里面看到了STRCMP是这样实现的，觉得有点问题，想提出来高手们讨论下
int strcmp(char *s,char *t)
{

int i;
for(i=0;s[i]==t[i];i++)
if(s[i]=='\0')
return 0;
return s[i]-t[i];
}

假设有 这两个字符串ABC ABCD 貌似这个算法不行啊
我看这么改行不：
int strcmp(char *s,char *t)
{

int i;
for(i=0;s[i]==t[i];i++)
if(s[i]=='\0'&&t[i]=='\0')
return 0;
return s[i]-t[i];
}

[jackyjkchen]

微软CRT的实现，不要去鸟那些教材，VC才是用于生产实践的

int __cdecl strcmp (
        const char * src,
        const char * dst
        )
{
        int ret = 0 ;

        while( ! (ret = *(unsigned char *)src - *(unsigned char *)dst) && *dst)
                ++src, ++dst;

        if ( ret < 0 )
                ret = -1 ;
        else if ( ret > 0 )
                ret = 1 ;

        return( ret );
}

[mstlq]

glibc的……

/* Copyright (C) 1991, 1996, 1997, 2003 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 Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 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
   Lesser General Public License for more details.

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

#include <string.h>
#include <memcopy.h>

#undef strcmp

/* Compare S1 and S2, returning less than, equal to or
   greater than zero if S1 is lexicographically less than,
   equal to or greater than S2. */
int
strcmp (p1, p2)
     const char *p1;
     const char *p2;
{
register const unsigned char *s1 = (const unsigned char *) p1;
register const unsigned char *s2 = (const unsigned char *) p2;
unsigned reg_char c1, c2;

do
    {
      c1 = (unsigned char) *s1++;
      c2 = (unsigned char) *s2++;
      if (c1 == '\0')
return c1 - c2;
    }
while (c1 == c2);

return c1 - c2;
}
libc_hidden_builtin_def (strcmp)

[muyiyj]

我觉得没必要添加，
你for中已经做了s[i]==t[i];判断
你if中就没必要添加&&t[i]=='\0'了

[mymtom]

#include <string.h>

/*
 * Compare strings.
 */
int
strcmp(const char *s1, const char *s2)
{
        while (*s1 == *s2++)
                if (*s1++ == 0)
                        return (0);
        return (*(const unsigned char *)s1 - *(const unsigned char *)(s2 - 1));
}

[huanmie_09]

问下楼主，你觉得这个程序怎么有问题了。我倒是觉得楼主添加的那个判断有点画蛇添足了.
注意for循环里的条件表达式为：s[i]==t[i];
if(s[i]=='\0') {
return 0;
}
是判断等长且各字符相等的两个字符串的时候.
其他不等的情况均可以由s[i]==t[i]来判断，若不成立，跳出for循环.
返回值为不相等的两个字符的差。

int strcmp(char *s,char *t)
{
  int i;
  for(i=0;s[i]==t[i];i++) {
    if(s[i]=='\0') {
      return 0;
    }
  }
  return s[i]-t[i];
}

[ypb362148418]

int __cdecl strcmp (
        const char * src,
        const char * dst
        )
{
        int ret = 0 ;

        while( ! (ret = *(unsigned char *)src - *(unsigned char *)dst) && *dst)
                ++src, ++dst;

        if ( ret < 0 )
                ret = -1 ;
        else if ( ret > 0 )
                ret = 1 ;

        return( ret );
}
//这个代码才是王道

[mymtom]

[Quote=引用 6 楼 ypb362148418 的回复:]

C/C++ code

int __cdecl strcmp (
const char * src,
const char * dst
)
{
int ret = 0 ;

while( ! (ret = *(unsigned char *)src - *(unsigned char *)dst) &&am……
[/Quote]
不觉得呀。

[JeffShen]

楼主，在你所列的程序中可能少写了一组“{}”
int strcmp(char *s ,char *t)
{
int i=0;
for(i=0;s[i]==t[i];i++)
{
if(s[i]=='\0')
return 0;
}
return s[i]-t[i];
}