C++ 高精度时钟获取当前时间 std::chrono::high_resolution_clock::now

C++ 高精度时钟获取当前时间 std::chrono::high_resolution_clock::now

• 1. `std::chrono::high_resolution_clock::now`
• • 1.1. Parameters
  • 1.2. Return value
  • 1.3. Example
• 2. `std::chrono::milliseconds`
• 3. `std::chrono::microseconds`
• • 3.1. Example
• References

1. std::chrono::high_resolution_clock::now

Get current time
https://cplusplus.com/reference/chrono/high_resolution_clock/now/

// public static member function static time_point now() noexcept; 

Returns the current time_point in the frame of the high_resolution_clock.

1.1. Parameters

none

1.2. Return value

The time_point representing the current time.

time_point is a member type, defined as an alias of time_point<high_resolution_clock>.

1.3. Example

#include <iostream> #include <ctime> #include <ratio> #include <chrono>  int main() { 	using namespace std::chrono;  	high_resolution_clock::time_point begin = high_resolution_clock::now();  	std::cout << "Printing out 1000 stars...\n"; 	for (int i = 0; i < 1000; ++i) { std::cout << "*"; } 	std::cout << std::endl;  	high_resolution_clock::time_point end = high_resolution_clock::now();  	duration<double> time_span = duration_cast<duration<double>>(end - begin);  	std::cout << "It took me " << time_span.count() << " seconds."; 	std::cout << std::endl;  	return 0; }  

Printing out 1000 stars... **************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************** It took me 0.0411305 seconds. 请按任意键继续. . . 

time_point is a member type, defined as an alias of time_point<high_resolution_clock>.

#include <iostream> #include <ctime> #include <ratio> #include <chrono>  int main() { 	using namespace std::chrono;  	time_point<high_resolution_clock> begin = high_resolution_clock::now();  	std::cout << "Printing out 1000 stars...\n"; 	for (int i = 0; i < 1000; ++i) { std::cout << "*"; } 	std::cout << std::endl;  	time_point<high_resolution_clock> end = high_resolution_clock::now();  	duration<double> time_span = duration_cast<duration<double>>(end - begin);  	std::cout << "It took me " << time_span.count() << " seconds."; 	std::cout << std::endl;  	return 0; } 

Printing out 1000 stars... **************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************** It took me 0.033101 seconds. 请按任意键继续. . . 

2. std::chrono::milliseconds

Duration in milliseconds

// class typedef duration < /* see rep below */, milli > milliseconds; 

Instantiation of duration to represent milliseconds.

A millisecond (from milli- and second; symbol: ms) is a unit of time in the International System of Units equal to one thousandth (0.001 or $10^{-3}$ or 1/1000) of a second or 1000 microseconds.

1 millisecond (1 ms)

3. std::chrono::microseconds

Duration in microseconds

// class typedef duration < /* see rep below */, micro > microseconds; 

Instantiation of duration to represent microseconds.

A microsecond is a unit of time in the International System of Units (SI) equal to one millionth (0.000001 or $10^{-6}$ or 1/1,000,000) of a second. Its symbol is μs, sometimes simplified to us when Unicode is not available.

1 microsecond (1 μs)

3.1. Example

#include <iostream> #include <ctime> #include <ratio> #include <chrono>  int main() { 	std::chrono::time_point<std::chrono::high_resolution_clock> begin = std::chrono::high_resolution_clock::now();  	std::cout << "Printing out 1000 stars...\n"; 	for (int i = 0; i < 1000; ++i) { std::cout << "*"; } 	std::cout << std::endl;  	std::chrono::time_point<std::chrono::high_resolution_clock> end = std::chrono::high_resolution_clock::now();  	std::chrono::milliseconds time_span_ms = std::chrono::duration_cast<std::chrono::milliseconds>(end - begin); 	std::chrono::microseconds time_span_us = std::chrono::duration_cast<std::chrono::microseconds>(end - begin);  	std::cout << "It took me " << time_span_ms.count() << " milliseconds (ms).\n"; 	std::cout << "It took me " << time_span_us.count() << " microseconds (us).\n"; 	std::cout << std::endl;  	return 0; }  

Printing out 1000 stars... **************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************** It took me 33 milliseconds (ms). It took me 33908 microseconds (us).  请按任意键继续. . . 

References

[1] Yongqiang Cheng, https://yongqiang.blog.csdn.net/