字符串查找，字符串包含，strstr

#include <stdio.h>
#include <string.h>
#include <assert.h>

char * mystrstr(char * str1, char * str2)
{
        assert(str1 && str2);

        char * main = str1, *sub = str2;
        int len1,len2;

        len2 = strlen(sub);
        if(len2 == 0)
                return NULL;

        len1 = strlen(main);

        if(len2 > len1) {
                return NULL;
        }

        while(len1 > 0) {
                len1--;
                if(len2 > len1)
                        return NULL;
                while(*main++ == *sub++) {
                        if(*sub == '\0')
                                break;
                }

                if(*sub == '\0') {
                        if(strlen(str1) < len2) {
                                return str1;
                        } else {
                                return (str1+len2);
                        }
                } else {
                        sub = str2;
                        main = ++ str1;
                }
        }
        return NULL;

}


int main() {
        char * main = "abiababdaaaefghiabgklzhaixishanabxxxx";
        char * sub = "zhaixishan";
        int count = 0;
       char * find = mystrstr(main,sub);

        while(find) {
                count ++;

                if(find) {
                        // printf("\n %s\n",find);

                }else {
                        printf("\ndonot find !!!\n");
                }
                find = mystrstr(find,sub);
        }
        printf("there is %d sub string in main string\n",count);
}



运行结果：
zhaixishan@zhaixishan-desktop:~/Desktop$ ./a.out
there is 1 count sub string in main string