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server-api-memcmp

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原型

The memcmp() function compares the first n bytes (each interpreted as unsigned char) of the memory areas s1 and s2.

用来比较s1和s2所指的内存区间前n个字符,进行比较操作时，假定两个不等的字节均为无符号字符(unsigned char)

函数原型
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// s1
//      要比较内存区域1
// s2
//      要比较内存区域2
// n
//      要比较的字节数
//
// return:
//      The memcmp() function returns an integer less than, equal to, or  greater  than  zero  if  the first  n bytes of s1 is found, respectively, to be less than, to match, or be greater than the first n bytes of s2.
//      若参数s1和s2所指的内存内容都完全相同则返回0值。s1若大于s2则返回大于0的值。s1若小于s2则返回小于0的值。
//
//
int memcmp(const void *s1, const void *s2, size_t n);

使用参考

简单的比较操作
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#include <string.h>
#include <strings.h>
#include <stdio.h>

int main()
{
    char *a = "aBcDeF";
    char *b = "AbCdEf";
    char *c = "aacdef";
    char *d = "aBcDeF";

    printf("memcmp(a,b):%d\n",memcmp((void*)a, (void*) b, 6));
    printf("memcmp(a,c):%d\n",memcmp((void*)a, (void*) c, 6));
    printf("memcmp(a,d):%d\n",memcmp((void*)a, (void*) d, 6));

    printf("bcmp(a,b):%d\n",bcmp((void*)a, (void*) b, 6));
    printf("bcmp(a,c):%d\n",bcmp((void*)a, (void*) c, 6));
    printf("bcmp(a,d):%d\n",bcmp((void*)a, (void*) d, 6));

    return 0;
}