c++学习笔记4：chrono 计时

要获取代码运行的时间，一个比较好的方式是使用chrono。

看例子，在两次获取时间的代码中间，休眠1s

#include 
#include 
#include 

int main() {
	using namespace std::literals::chrono_literals;

	auto start = std::chrono::high_resolution_clock::now();

	std::this_thread::sleep_for(1s);

	auto end = std::chrono::high_resolution_clock::now();

	std::chrono::duration duration = end - start;

	std::cout << duration.count() << "s" << std::endl;

	std::cin.get();
}

输出大致为1秒：

1.00451s

再看forloop打印100次的时间：

#include 
#include 
#include 

struct Timer {
	std::chrono::time_point start, end;
	std::chrono::duration duration;

	Timer(){
		start = std::chrono::high_resolution_clock::now();
	}

	~Timer() {
		end = std::chrono::high_resolution_clock::now();
		duration = end - start;
		float ms = duration.count()*1000.0f;
		std::cout << "Timer took " << ms << "ms" << std::endl;
	}
};

void func() {
	Timer timer;

	for (int i = 0;i < 100;i++)
		std::cout << "hello" << std::endl;
}

int main() {
	func();

	std::cin.get();
}

代码做了结构化调整，将相关功能都提取到一个结构中，然后在func函数中创建一个Timer，当func执行完毕，Timer自动析构。输出为：

hello
hello
hello
hello
hello
hello
hello
hello
hello
hello
hello
hello
hello
hello
hello
hello
hello
hello
hello
hello
hello
hello
hello
hello
Timer took 105.268ms

如果去掉std::cout << "hello" << std::endl; 语句的std::endl，再看执行时间：

lohelloTimer took 4.839ms