c++判断文件是否存在

#include <string>
#include <unistd.h>
#include <string.h>
#include <iostream>
#include <vector>
using namespace std;

int main(){

    string filename_1 = "/home/cai/CLionProjects/socket_demo/file_test/get_file_create_time.cpp";
    string filename_3 = filename_1.append("");
    char filename_4[filename_3.size()];
    strcpy(filename_4 , filename_3.c_str());
    if (access(filename_4, 0) == -1) {
        std::cout<<"dddddd" <<std::endl;
    } else{
        std::cout<<"DDDDDD" <<std::endl;
    }

}