cin后如何删除一行？

#include <stdio.h>

int main() {
    FILE *fp = fopen("filename.txt", "r+");
    FILE *tmp = tmpfile();
    char buffer[100];
    int line_number = 1;
    
    if (fp == NULL) {
        printf("Failed to open file.\n");
        return 1;
    }
    
    while (fgets(buffer, sizeof(buffer), fp) != NULL) {
        // 判断是否需要删除该行，这里假设需要删除第3行
        if (line_number == 3) {
            line_number++;
            continue;
        }
        
        fputs(buffer, tmp);
        line_number++;
    }
    
    fclose(fp);
    fclose(tmp);
    
    if (rename("tmpfile.txt", "filename.txt") != 0) {
        printf("Failed to rename file.\n");
        return 1;
    }
    
    printf("Line deleted successfully.\n");
    
    return 0;
}