C语言之memcmp函数

来源：互联网发布：网络监测基础与实战编辑：程序博客网时间：2024/06/05 06:19

【FROM MSDN && 百科】

原型：　int memcmp(const void *buf1, const void *buf2, unsigned int count);

#include<string.h>

比较内存区域buf1和buf2的前count个字节。此函数是按字节比较。

Compares the first num bytes of the block of memory pointed by ptr1 to the first num bytes pointed by ptr2, returning zero if they all match or a value different from zero representing which is greater if they do not。

Notice that, unlike strcmp, the function does not stop comparing after finding a null character.

对于memcmp()，如果两个字符串相同而且count大于字符串长度的话，memcmp不会在\0处停下来，会继续比较\0后面的内存单元，如果想使用memcmp比较字符串，要保证count不能超过最短字符串的长度，否则结果有可能是错误的。

DEMO:

//#define FIRST_DEMO#define MYMEMCMP#ifdef FIRST_DEMO#include <stdio.h>#include <conio.h>#include <string.h>int main(void){char *s1="Hello, Programmers!";char *s2="Hello, Programmers!";int r;r=memcmp(s1,s2,50/*strlen(s1)*/);if (!r){printf("s1 and s2 are identical!\n");}else if (r<0){printf("s1 less than s2\n");}else{printf("s1 greater than s2\n");}getch();return 0;}#elif defined MYMEMCMP#include <stdio.h>#include <conio.h>#include <string.h>int mymemcmp(const void *buffer1,const void *buffer2,int ccount);void Print(char *str1,char *str2,int t);int main(void){    char *str1="hel";char *str2="hello";Print(str1,str2,mymemcmp(str1,str2,3));Print(str2,str1,mymemcmp(str2,str1,3));Print(str2,str2,mymemcmp(str2,str2,3));getch();return 0;}/*FROM:http://blog.chinaunix.net/uid-20480343-id-1941630.html */int mymemcmp(const void *buffer1,const void *buffer2,int count){if (!count){return 0;}while(count && *(char *)buffer1==*(char *)buffer2){count--;buffer1=(char *)buffer1-1;buffer2=(char *)buffer2-1;}return (*((unsigned char *)buffer1)- *((unsigned char *)buffer2));}void Print(char *str1,char *str2,int t){if (t>0){printf("\n%s Upper than %s \n",str1,str2);}else if(t<0){printf("\n%s Lower than %s \n",str1,str2);}else{printf("\n%s equal %s \n",str1,str2);}}#endif