cpp measure elapsed time

measure_elapsed.cpp

// c++11 is required

#include <chrono>
#include <string>
#include <iostream>

class Instant {
    std::string description;
    std::chrono::time_point<std::chrono::steady_clock> start;

public:
    Instant() {
        new (this)Instant("");
    }
    Instant(std::string desc): description(desc) {
        start = std::chrono::steady_clock::now();
    }

    std::chrono::milliseconds elapsed_ms() {
        std::chrono::steady_clock::time_point now = std::chrono::steady_clock::now();

        return std::chrono::duration_cast<std::chrono::milliseconds> (now - start);
    }

    void print_elapsed_ms() {
        auto elapsed = elapsed_ms();
        std::string sep = description.empty()? "" : ",";
        std::cout<< description << sep << "elapsed: " << elapsed.count() <<  "[ms]" << std::endl;
    }
};

int main() {
    auto instant = Instant();
    instant.print_elapsed_ms();
    return 0;
}