C++实现统计代码运行时间的示例详解

目录

• 纯标准库实现
• 类似C#的实现
• 总结

本来想自己写的，一看github上面都有就不再重复造轮子了。github上的项目如下：

• StopWatch 纯标准库实现：使用std::chrono::high_resolution_clock，其实就是std::chrono::steady_clock的别名。
• StopWatch 类似C#的实现：和C#的StopWatch比较像，在Windows下使用的是QueryPerformanceCounter系统API，其它系统下使用std::chrono::steady_clock。

纯标准库实现

第一种纯标准库实现的Stopwatch.hpp内容如下：

// Copyright Ingo Proff 2017.
// https://github.com/CrikeeIP/Stopwatch
// Distributed under the MIT Software License (X11 license).
// (See accompanying file LICENSE)

#pragma once

#include <vector>
#include <string>
#include <chrono>

namespace stopwatch{

class Stopwatch{
public:
   enum TimeFormat{ NANOSECONDS, MICROSECONDS, MILLISECONDS, SECONDS };

   Stopwatch(): start_time(), laps({}) {
      start();
   }

   void start(){
      start_time = std::chrono::high_resolution_clock::now();
      laps = {start_time};
   }

   template<TimeFormat fmt = TimeFormat::MILLISECONDS>
   std::uint64_t lap(){
      const auto t = std::chrono::high_resolution_clock::now();
      const auto last_r = laps.back();
      laps.push_back( t );
      return ticks<fmt>(last_r, t);
   }

   template<TimeFormat fmt = TimeFormat::MILLISECONDS>
   std::uint64_t elapsed(){
      const auto end_time = std::chrono::high_resolution_clock::now();
      return ticks<fmt>(start_time, end_time);
   }

   template<TimeFormat fmt_total = TimeFormat::MILLISECONDS, TimeFormat fmt_lap = fmt_total>
   std::pair<std::uint64_t, std::vector<std::uint64_t>> elapsed_laps(){
      std::vector<std::uint64_t> lap_times;
      lap_times.reserve(laps.size()-1);

      for( std::size_t idx = 0; idx <= laps.size()-2; idx++){
         const auto lap_end = laps[idx+1];
         const auto lap_start = laps[idx];
         lap_times.push_back( ticks<fmt_lap>(lap_start, lap_end) );
      }

      return { ticks<fmt_total>(start_time, laps.back()), lap_times };
   }


private:
   typedef std::chrono::time_point<std::chrono::high_resolution_clock> time_pt;
   time_pt start_time;
   std::vector<time_pt> laps;

   template<TimeFormat fmt = TimeFormat::MILLISECONDS>
   static std::uint64_t ticks( const time_pt& start_time, const time_pt& end_time){
      const auto duration = end_time - start_time;
      const std::uint64_t ns_count = std::chrono::duration_cast<std::chrono::nanoseconds>(duration).count();

      switch(fmt){
      case TimeFormat::NANOSECONDS:
      {
         return ns_count;
      }
      case TimeFormat::MICROSECONDS:
      {
         std::uint64_t up = ((ns_count/100)%10 >= 5) ? 1 : 0;
         const auto mus_count = (ns_count /1000) + up;
         return mus_count;
      }
      case TimeFormat::MILLISECONDS:
      {
         std::uint64_t up = ((ns_count/100000)%10 >= 5) ? 1 : 0;
         const auto ms_count = (ns_count /1000000) + up;
         return ms_count;
      }
      case TimeFormat::SECONDS:
      {
         std::uint64_t up = ((ns_count/100000000)%10 >= 5) ? 1 : 0;
         const auto s_count = (ns_count /1000000000) + up;
         return s_count;
      }
      }
    }
};


constexpr Stopwatch::TimeFormat ns = Stopwatch::TimeFormat::NANOSECONDS;
constexpr Stopwatch::TimeFormat mus = Stopwatch::TimeFormat::MICROSECONDS;
constexpr Stopwatch::TimeFormat ms = Stopwatch::TimeFormat::MILLISECONDS;
constexpr Stopwatch::TimeFormat s = Stopwatch::TimeFormat::SECONDS;

constexpr Stopwatch::TimeFormat nanoseconds = Stopwatch::TimeFormat::NANOSECONDS;
constexpr Stopwatch::TimeFormat microseconds = Stopwatch::TimeFormat::MICROSECONDS;
constexpr Stopwatch::TimeFormat milliseconds = Stopwatch::TimeFormat::MILLISECONDS;
constexpr Stopwatch::TimeFormat seconds = Stopwatch::TimeFormat::SECONDS;


std::string show_times( const std::vector<std::uint64_t>& times ){
    std::string result("{");
    for( const auto& t : times ){
        result += std::to_string(t) + ",";
    }
    result.back() = static_cast<char>('}');
    return result;
}

}

使用示例如下：

//创建一个stopwatch
sw::Stopwatch my_watch;
my_watch.start();

//Do something time-consuming here...

//纳秒
std::uint64_t elapsed_ns = my_watch.elapsed<sw::ns>();
//微秒
std::uint64_t elapsed_mus = my_watch.elapsed<sw::mus>();
//毫秒
std::uint64_t elapsed_ms = my_watch.elapsed();
//秒
std::uint64_t elapsed_s = my_watch.elapsed<sw::s>();

类似C#的实现

第二种类似C#的实现，StopWatch.h代码如下：

#ifndef __STOPWATCH_H__
#define __STOPWATCH_H__

#if defined(_MSC_VER) || defined(__MINGW32__) || defined(WIN32)
#include <Windows.h>
#else
#include <chrono>
#endif

class StopWatch
{
public:
	StopWatch();
	~StopWatch();

	//开启计时
	void Start();

	//暂停计时
	void Stop();

	//重新计时
	void ReStart();

	//微秒
	double Elapsed();

	//毫秒
	double ElapsedMS();

	//秒
	double ElapsedSecond();

private:
	long long elapsed_;
#if defined(_MSC_VER) || defined(__MINGW32__) || defined(WIN32)
	LARGE_INTEGER start_;
	LARGE_INTEGER stop_;
	LARGE_INTEGER frequency_;
#else
	typedef std::chrono::high_resolution_clock Clock;
	typedef std::chrono::microseconds MicroSeconds;
	std::chrono::steady_clock::time_point start_;
	std::chrono::steady_clock::time_point stop_;
#endif
	
};

#endif // __STOPWATCH_H__

StopWatch.cpp代码如下：

#include "StopWatch.h"

#if defined(_MSC_VER) || defined(__MINGW32__) || defined(WIN32)
StopWatch::StopWatch():elapsed_(0)
{
		elapsed_ = 0;
		start_.QuadPart = 0;
		stop_.QuadPart = 0;
		QueryPerformanceFrequency(&frequency_);
}
#else
StopWatch::StopWatch():elapsed_(0),start_(MicroSeconds::zero()),stop_(MicroSeconds::zero())
{
}
#endif

StopWatch::~StopWatch()
{
}

void StopWatch::Start()
{
#if defined(_MSC_VER) || defined(__MINGW32__) || defined(WIN32)
	QueryPerformanceCounter(&start_);
#else
	start_ = Clock::now();
#endif
	
}

void StopWatch::Stop()
{
#if defined(_MSC_VER) || defined(__MINGW32__) || defined(WIN32)
	QueryPerformanceCounter(&stop_);
	elapsed_ += (stop_.QuadPart - start_.QuadPart) * 1000000 / frequency_.QuadPart;
#else
	stop_ = Clock::now();
	elapsed_ = std::chrono::duration_cast<MicroSeconds>(stop_ - start_).count();
#endif
	
}

void StopWatch::ReStart()
{
	elapsed_ = 0;
	Start();
}

double StopWatch::Elapsed()
{
	return static_cast<double>(elapsed_);
}

double StopWatch::ElapsedMS()
{
	return elapsed_ / 1000.0;
}

double StopWatch::ElapsedSecond()
{
	return elapsed_ / 1000000.0;
}

使用示例如下（和C#比较像）：

StopWatch sw;
sw.Start();
//Do something time-consuming here...
sw.Stop();
std::cout << "运行时间：" << sw.ElapsedMS() << "毫秒" << std::endl;

总结

• 如果有代码洁癖的话就使用第一种，纯标准库实现、功能全面、使用方法偏向传统C++。
• 如果不介意使用系统API的话就使用第二种，功能简单、使用方法偏向传统C#。

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