Find if a string exists in a file

//Check the chain in the file /tmp/.ipt, whether it has already existed.
// return 1 (already existed) return 0 (not find)

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


int check_ipt_existed_chain(char *find_str)
{
    FILE *fp;
    char *find;
    char buf_tmp[256] = "";
    fp = fopen("./tmp/.ipt", "r");

    if (fp == NULL)
    {
        printf("error\n");
        return 0;
    }

    while(fgets(buf_tmp, sizeof(buf_tmp), fp) != NULL)
    {
        find = strstr(buf_tmp, find_str);
        if(find  != NULL)
        {
            return 1;
        }
    }

    return 0;
}

int main()
{
    int x;
    x = check_ipt_existed_chain(":TR69_RULES");
    printf("x:%d\n",x);

    return 0;
}