SetTimer.cpp

#include <chrono>
#include <string>
#include <fstream>
#include <iomanip>
#include <sstream>
#include <iostream>
#include <filesystem>
using namespace std;
using namespace chrono;
using namespace filesystem;

string getNewTime();
void overwriteFile(const string& path, const string& text);

int main(int, char** argv) {
    const path loc{path{argv[0]}.parent_path() / "Alerm.txt"};
    const string newTime{getNewTime()};
    overwriteFile(loc.string(), newTime);
    return 0;
}

string getNewTime() {
    time_point nowt{system_clock::now()};
    minutes m{30};
    system_clock::duration d{m};
    nowt += d;

    const time_t nowc{system_clock::to_time_t(nowt)};
    stringstream ss;
    ss << put_time(localtime(&nowc), "%H:%M:%S");
    return ss.str();
}

void overwriteFile(const string& path, const string& text) {
    ofstream ofs{path, ios_base::out};
    ofs << text << '\n';
}