C语言，比较2个日期的大小

//盗墓者是个丑奴儿，原

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

 

//结构体转为毫秒，返回time_t 类型

time_t Transformation(struct tm t){
        return mktime(&t);
}

int main(void){


        struct tm t1={0};
        struct tm t2={0};

        t1.tm_year=2018;
        t1.tm_mon=7;
        t1.tm_mday=21;

        t2.tm_year=2019;
        t2.tm_mon=7;
        t2.tm_mday=21;

        time_t t1_l=Transformation(t1);
        time_t