如何测试代码执行耗时？

#include <chrono>
#include <ctime>
class Timer
{
public:
	Timer() :running_(false),
		has_run_at_least_once_(false)
	{

	}
	virtual ~Timer()
	{

	}
	virtual void Start()
	{
		if (!running())
		{
			start_cpu_ = std::chrono::high_resolution_clock::now();
			running_ = true;
			has_run_at_least_once_ = true;
		}
	}
	virtual void Stop()
	{
		if (running())
		{
			stop_cpu_ = std::chrono::high_resolution_clock::now();
			running_ = false;
		}
	}
	virtual float Nanoseconds()
	{
		if (!has_run_at_least_once())
		{
			printf("Timer has never been run before reading time.");
			return 0;
		}
		return std::chrono::duration_cast<std::chrono::nanoseconds>(stop_cpu_ - start_cpu_).count();
	}
	virtual float MilliSeconds()
	{
		if (!has_run_at_least_once())
		{
			printf("Timer has never been run before reading time.");
			return 0;
		}
		return std::chrono::duration_cast<std::chrono::milliseconds>(stop_cpu_ - start_cpu_).count();
	}
	virtual float MicroSeconds()
	{
		if (!has_run_at_least_once())
		{
			printf("Timer has never been run before reading time.");
			return 0;
		}
		return std::chrono::duration_cast<std::chrono::microseconds>(stop_cpu_ - start_cpu_).count();
	}
	virtual float Seconds()
	{
		return MilliSeconds() / 1000.0;
	}
	inline bool running() { return running_; }
	inline bool has_run_at_least_once() { return has_run_at_least_once_; }
private:
	bool running_;
	bool has_run_at_least_once_;
	std::chrono::high_resolution_clock::time_point start_cpu_;
	std::chrono::high_resolution_clock::time_point stop_cpu_;
};