使用C++的find()函数，实现从一个文件中查找一个字符串的程序

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

#define MAX_LEN 100

int main() {
    char filename[MAX_LEN], search_str[MAX_LEN];
    printf("Enter filename: ");
    scanf("%s", filename);
    printf("Enter string to search: ");
    scanf("%s", search_str);

    FILE *fp = fopen(filename, "r");
    if (fp == NULL) {
        printf("Failed to open file.\n");
        return 1;
    }

    char line[MAX_LEN];
    int line_num = 1, found = 0;
    while (fgets(line, MAX_LEN, fp) != NULL) {
        char *pos = strstr(line, search_str);
        if (pos != NULL) {
            printf("Found \"%s\" in line %d: %s", search_str, line_num, line);
            found = 1;
        }
        line_num++;
    }

    if (!found) {
        printf("String \"%s\" not found in file.\n", search_str);
    }

    fclose(fp);
    return 0;
}