Unable to create a folder with todays date in c++ - c++

Question

Im trying to create a folder with todays date in c++. WHile in python its very easy , in c++ im finding it challenging.
I tried this code where first I tried to print the date and then use the date values to create a folder. I even tried inserting unix commands but even those didnt work.
I simply want to create a directory like : DD_MM_YYYY or DD_MM_YY
#include <bits/stdc++.h>
#include <iostream>
#include <sys/stat.h>
#include <sys/types.h>
#include "time.h"
//#include "date/tz.h"
using namespace std;
using namespace std::chrono;
int main()
{ //option 1
time_t my_time =time(NULL);
cout << ctime(&my_time)<<endl;
///option 2
time_t t = time(NULL);
struct tm tm = *localtime(&t);
printf("now: %d-%d-%d %d:%d:%d\n", tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday, tm.tm_hour, tm.tm_min, tm.tm_sec);
printf("Date: %d_%d_%d\n", tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday);
// EXPERIMENT SECTION : ALL OF THESE THROWING ERRORS
//sub_fol=(tm.tm_year+1900).ToString()+"."+tm.tm_mon.ToString();
//sub_fol=tm.tm_mon;
string str="date +'%d_%m_%y'";
//str="mkdir "+ str;
const char *command=str.c_str();
//string dr=system(command);
//printf(string(tm.tm_mon));
// THIS ONES WORKING
if (mkdir("test_", 0777) == -1)
cerr << "Error : " << strerror(errno) << endl;
else
cout << "Directory created";
// THIS ONE ISNT WORKING
if (mkdir(system(command), 0777) == -1)
cerr << "Error : " << strerror(errno) << endl;
else
cout << "Directory created";
}

Answer 1

You can make use of std::localtime and std::puttime to get a formatted date.
For example:
#include <iostream>
#include <chrono>
#include <sstream>
#include <iomanip>
int main()
{
auto const now = std::chrono::system_clock::now();
auto const in_time_t = std::chrono::system_clock::to_time_t(now);
std::stringstream ss;
ss << std::put_time(std::localtime(&in_time_t), "%d_%m_%Y");
std::cout << ss.str() << std::endl;
}
Will get you:
14_01_2021
You can see https://en.cppreference.com/w/cpp/io/manip/put_time for more formatting options.
Then you can use mkdir or make use of std::filesystem if you are using C++17 or above.
#include <filesystem>
...
std::filesystem::create_directory("abc");
See https://en.cppreference.com/w/cpp/filesystem/create_directory
For mkdir it expects a const char *path rather than a std::string but you can get a char pointer via c_str() e.g.:
mkdir(ss.str().c_str(), 0700);