I needed to implement a stop watch like class that will be used to measure running time of different functions by others. The final running time needs to be printed in 9h 3min 2s 23s 32ms 87us 78ns format. If the larger units are zero then they must be omitted. Time duration in a particular time-unit like seconds or milliseconds can be obtained from functions similar to hours. I need better ideas to improve the implementation.

#ifndef _STOP_WATCH_HPP_ #define _STOP_WATCH_HPP_  #include <chrono> #include <utility> #include <iostream>  class stop_watch {     std::chrono::high_resolution_clock::time_point last_time_point;     std::chrono::duration<double> time_duration;     bool is_running;   public:     stop_watch() :        last_time_point {std::chrono::high_resolution_clock::now()},       time_duration {std::chrono::duration<double>::zero()},       is_running {false}       {}     void start() {       assert(!is_running); // stop watch is already running       last_time_point = std::chrono::high_resolution_clock::now();       time_duration = std::chrono::duration<double>::zero();       is_running = true;     }     void stop() {       assert(is_running); // stop watch is not running       auto n = std::chrono::high_resolution_clock::now();       time_duration = n - last_time_point;       last_time_point = n;       is_running = false;     }     double hours() {       return std::chrono::duration_cast<std::chrono::hours>(           time_duration).count();     }     friend std::ostream& operator<<(std::ostream& out, stop_watch sw) {       std::chrono::hours h = std::chrono::duration_cast<           std::chrono::hours>(sw.time_duration);       if (h.count()) {out << h.count() << "h "; sw.time_duration -= h;}       std::chrono::minutes m = std::chrono::duration_cast<           std::chrono::minutes>(sw.time_duration);       if (m.count()) {out << m.count() << "min "; sw.time_duration -= m;}       std::chrono::seconds s = std::chrono::duration_cast<           std::chrono::seconds>(sw.time_duration);       if (s.count()) {out << s.count() << "s "; sw.time_duration -= s;}       std::chrono::milliseconds ms = std::chrono::duration_cast<           std::chrono::milliseconds>(sw.time_duration);       if (ms.count()) {out << ms.count() << "ms "; sw.time_duration -= ms;}       std::chrono::microseconds us = std::chrono::duration_cast<           std::chrono::microseconds>(sw.time_duration);       if (us.count()) {out << us.count() << "us "; sw.time_duration -= us;}       std::chrono::nanoseconds ns = std::chrono::duration_cast<           std::chrono::nanoseconds>(sw.time_duration);       if (ns.count()) {out << ns.count() << "ns "; sw.time_duration -= ns;}       return out;     } };  #endif 

Sample usage

stop_watch sw; sw.start(); // function(s) to measure time sw.stop(); cout << "It took " << sw << endl; 

I need some guideline on how to do this more efficiently, as my code is already too messy :(. I also have the following questions:

1. Is there a way to generate the functions for hours, seconds, etc. dynamically?
2. How can I improve the operator<< function? Is there a way to have a list of time units that I can iterate?