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【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 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);
- 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;
- }
-
- 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
memcmp按字节比较,可以设置比较的位数
strcmp按字符比较,只能比较整个字符串
都是用ASCII码进行比较,效率在数量级上不会相差太大的
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