strcmp函数
【摘要】 #include <stdio.h>#include <assert.h> int strcmp(char const *str1, char const *str2){ int ret = 0; assert(str1 != NULL && str2 != NULL); while ( ! (ret = *(unsigned ch...
-
#include <stdio.h>
-
#include <assert.h>
-
-
-
int strcmp(char const *str1, char const *str2)
-
{
-
int ret = 0;
-
assert(str1 != NULL && str2 != NULL);
-
-
while ( ! (ret = *(unsigned char*)str1 - *(unsigned char*)str2) && *str1)
-
{//如果当前字符相等，且前面一个指针不为空，则指针后移;
-
//判断指针是否为空是为了防止两个字串相等时的负作用
-
str1++;
-
str2++;
-
}
-
-
return ((ret>0)-(-ret>0));
-
}
-
-
-
int main()
-
{
-
char s[100];
-
char p[100];
-
gets(s);
-
gets(p);
-
-
if (strcmp(s,p) > 0)
-
{
-
printf("s is bigger than p\n");
-
}
-
else if (strcmp(s,p) < 0)
-
{
-
printf("s is smaller than p\n");
-
}
-
else
-
{
-
printf("s is equal to p\n");
-
}
-
-
return 0;
-
}
//linux源码
-
/**
-
* strcmp - Compare two strings
-
* @cs: One string
-
* @ct: Another string
-
*/
-
#undef strcmp
-
int strcmp(const char *cs, const char *ct)
-
{
-
unsigned char c1, c2;
-
-
while (1) {
-
c1 = *cs++; //这里包含一个强制类型转换
-
c2 = *ct++;
-
if (c1 != c2)
-
return c1 < c2 ? -1 : 1;
-
if (!c1)
-
break;
-
}
-
return 0;
-
}
-
/***
-
*strcmp - compare two strings, returning less than, equal to, or greater than
-
*
-
*Purpose:
-
* STRCMP compares two strings and returns an integer
-
* to indicate whether the first is less than the second, the two are
-
* equal, or whether the first is greater than the second.
-
*
-
* Comparison is done byte by byte on an UNSIGNED basis, which is to
-
* say that Null (0) is less than any other character (1-255).
-
*
-
*Entry:
-
* const char * src - string for left-hand side of comparison
-
* const char * dst - string for right-hand side of comparison
-
*
-
*Exit:
-
* returns -1 if src < dst
-
* returns 0 if src == dst
-
* returns +1 if src > dst
-
*
-
*Exceptions:
-
*
-
*******************************************************************************/
-
-
int __cdecl strcmp (
-
const char * src,
-
const char * dst
-
)
-
{
-
int ret = 0 ;
-
-
while( ! (ret = *(unsigned char *)src - *(unsigned char *)dst) && *dst) //直到src和dst当前数值不相等且dst不为\0时退出while
-
++src, ++dst;
-
-
if ( ret < 0 )
-
ret = -1 ;
-
else if ( ret > 0 )
-
ret = 1 ;
-
-
return( ret );
-
}
//汇编源码
-
int strcmp(const char *str1, const char *str2)
-
{
-
__asm //内联汇编开始
-
{
-
mov eax ,str1 //str1 是指针，在内嵌汇编中，会自动转成 " mov eax , dword ptr [str1] "
-
mov ebx ,str2
-
xor ecx, ecx
-
_loop:
-
push eax
-
push ebx
-
movsx eax ,[eax]
-
movsx ebx ,[ebx]
-
cmp eax ,ecx
-
je eqends
-
cmp eax , ebx
-
jne neq
-
pop ebx
-
pop eax
-
inc eax
-
inc ebx
-
jmp _loop
-
eqends:
-
cmp ecx ,ebx //也就是0与ebx比较
-
jne neq
-
jmp _eq
-
-
neq:
-
mov eax , 1
-
jl small
-
jmp exit
-
small: neg eax
-
jmp exit
-
_eq:
-
xor eax ,eax
-
exit:
-
add esp , 8
-
}
-
}
文章来源: blog.csdn.net，作者：悦来客栈的老板，版权归原作者所有，如需转载，请联系作者。
原文链接：blog.csdn.net/qq523176585/article/details/11890661
【版权声明】本文为华为云社区用户转载文章，如果您发现本社区中有涉嫌抄袭的内容，欢迎发送邮件进行举报，并提供相关证据，一经查实，本社区将立刻删除涉嫌侵权内容，举报邮箱：
cloudbbs@huaweicloud.com
- 点赞
- 收藏
- 关注作者
评论（0）