A stopwatch accurate to milliseconds.

stopwatch.cc

// Author: keyou
// https://github.com/keyou

// A stopwatch accurate to milliseconds.
// compile command: g++ -std=c++11 -O3 stopwatch.cc -o stopwatch

#include <iostream>
#include <numeric>
#include <chrono>
#include <thread>
#include <iomanip>

int main() {
    auto start_time = std::chrono::steady_clock::now();
    while(true) {
        auto time = std::chrono::steady_clock::now()-start_time;
        auto millseconds = std::chrono::duration_cast<std::chrono::milliseconds>(time).count();
        std::cout << std::setfill('0') << std::setw(2) << millseconds/1000/60/60 << ":"
                  << std::setfill('0') << std::setw(2) << millseconds/1000/60%60 << ":"
                  << std::setfill('0') << std::setw(2) << millseconds/1000%60 << "."
                  << std::setfill('0') << std::setw(3) << millseconds%1000 << "\r";
        std::cout.flush();
        std::this_thread::sleep_for(std::chrono::milliseconds(1));
    }
    return 0;
}