将mcl中与系统相关的函数用c++标准库替代

1、判断文件是否存在，存在则删除

#include<stdio.h>#include<iostream>int main(void){    char *filename = "who.txt";    FILE * f;    f = fopen(filename,"r");    if (f == 0)        printf("file not exist");    else        {        remove(filename);        printf("file exist");        }    system("pause");    return 0;}

2、gettimeofday

#include<chrono>#include<iostream>int main(){    std::chrono::high_resolution_clock::time_point tm_now = std::chrono::high_resolution_clock::now();    std::chrono::steady_clock::duration tm_s =tm_now.time_since_epoch();    std::cout << tm_s.count() << std::endl;    time_t t_sec = (tm_s.count() / 1000000000);    int t_msec = (tm_s.count() - tm_s.count() / 1000000000 * 1000000000) / 1000000;    std::cout << t_sec << std::endl;    std::cout << t_msec << std::endl;    system("pause");    return 0;}