c语言如何判断一个字符串是不是一个字符串的字串

#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int find(char *buf, char* sub) {
    int len = strlen(buf);
    char *p = (char*)malloc(len * 2 + 1);
    memset(p, 0x00, len * 2 + 1);

    strcpy(p, buf);
    strcat(p, buf);

    if (strstr(p, sub) == NULL)
        return 0;
    else
        return 1;
}

int main(void) {
    char  buf[] = "abcdefg";
    if (find(buf, "bcdefga") == 1)
        printf("是子串\n");
    else
        printf("不是子串\n");
    system("pause");
}