不用已有的系统调用和库函数实现strstr()

#include<stdio.h>
#include<unistd.h>


char *my_strstr(char *,char *);

int
main(int argc,char *argv[])
{

        char *presult;
        if(3!=argc){
                printf("Usage:%s \n",argv[0]);
                exit(1);
        }
        presult=my_strstr(argv[1],argv[2]);
        printf("%s\n",presult);
        exit(0);
}

char *my_strstr(char *str,char *sub_str)
{
        int i=0,j=0;
        while(str[i]!='\0'&&sub_str[j]!='\0') {
                if(str[i]==sub_str[j]) {
                        i++;
                        j++;
                }
                else {
                        i=i-j+1;
                        j=0;
                }
        }
        if(sub_str[j]=='\0')
                return (char *)(str+i-j);
        return NULL;
}


上面的主程序是zhozj0222（cuID）实现的，他利用了指针的下标形式，来解决循环比较问题。。