问题描述
让我通过这个测试程序提出我的问题：
Let me ask my question by this test program:
#include <iostream>
#include <chrono>
using std::chrono::nanoseconds;
using std::chrono::duration_cast;
int main(int argc, char* argv[])
{
std::cout << "resolution (nano) = " << (double) std::chrono::high_resolution_clock::period::num
/ std::chrono::high_resolution_clock::period::den * 1000 * 1000 * 1000 << std::endl;
auto t1 = std::chrono::high_resolution_clock::now();
std::cout << "how much nanoseconds std::cout takes?" << std::endl;
auto t2 = std::chrono::high_resolution_clock::now();
auto diff = t2-t1;
nanoseconds ns = duration_cast<nanoseconds>(diff);
std::cout << "std::cout takes " << ns.count() << " nanoseconds" << std::endl;
return 0;
}
在我的机器上输出：
分辨率（纳米）= 100
多少纳秒std :: cout需要多少？
how much nanoseconds std::cout takes?
std :: cout需要1000200纳秒
std::cout takes 1000200 nanoseconds
我收到 1000200 或 1000300 或 1000400 或 1000500 code> 1000600 或 2000600 （= 1或2微秒）。显然， std :: chrono 的解析度为不 100纳秒或 std :: cout 错误。 （为什么我从来没有收到介于1到2微秒之间的东西，例如 1500000 ？）
I receive either 1000200 or 1000300 or 1000400 or 1000500 or 1000600 or 2000600 as a result (= 1 or 2 microsecond). Obviously either the resolution of std::chrono is not 100 nano-seconds or the way I measure the time of std::cout is wrong. (why I never receive something between 1 and 2 microseconds, for example 1500000?)
分辨率定时器在C ++。操作系统本身提供了一个高分辨率的定时器，因为我可以在同一台机器上使用C＃ Stopwatch 类来测量微秒精度。所以我只需要正确使用操作系统的高分辨率定时器！
I need a high-resolution timer in C++. The OS itself provides a high-resolution timer because I'm able to measure things with microsecond-precision using C# Stopwatch class on the same machine. So I would just need to correctly use the high-resolution timer that the OS has!
如何修复我的程序产生预期的结果？
How do I fix my program to produce the expected results?
推荐答案
我猜你在使用VS2012;如果没有，忽略这个答案。 VS2012 typedef 的 high_resolution_clock 到 system_clock 。可悲的是，这意味着它有精确的精度（大约1ms）。我写了一个更好的高res时钟，使用 QueryPerformanceCounter 在VS2012 ...
I'm going to guess you are using VS2012; If not, disregard this answer. VS2012 typedef's high_resolution_clock to system_clock. Sadly, this means it has crappy precision (around 1ms). I wrote a better high res clock which uses QueryPerformanceCounter for use in VS2012...
HighResClock。 h：
struct HighResClock
{
typedef long long rep;
typedef std::nano period;
typedef std::chrono::duration<rep, period> duration;
typedef std::chrono::time_point<HighResClock> time_point;
static const bool is_steady = true;
static time_point now();
};
HighResClock.cpp：
namespace
{
const long long g_Frequency = []() -> long long
{
LARGE_INTEGER frequency;
QueryPerformanceFrequency(&frequency);
return frequency.QuadPart;
}();
}
HighResClock::time_point HighResClock::now()
{
LARGE_INTEGER count;
QueryPerformanceCounter(&count);
return time_point(duration(count.QuadPart * static_cast<rep>(period::den) / g_Frequency));
}
（我省略了一个断言和#ifs看看是否被编译2012从上述代码）
(I left out an assert and #ifs to see if it's being compiled on 2012 from the above code)
您可以在任何地方使用此时钟，与标准时钟一样。
You can use this clock anywhere and in the same way as standard clocks.
这篇关于分辨率std :: chrono :: high_resolution_clock不对应测量的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！