Question

考虑以下代码，它将始终显示某些代码的最慢执行时间：

std::chrono::steady_clock::time_point begin, end
std::chrono::duration_cast<std::chrono::microseconds> lastElapsed;

begin = std::chrono::steady_clock::now();

... some processing to be measured ...

end = std::chrono::steady_clock::now();
auto elapsed = std::chrono::duration_cast<std::chrono::microseconds>(end - begin).count();

if (elapsed > lastElapsed)
{
    std::cout << "The slowest execution interval is now at  " << elapsed << "us" << std::endl;
    lastElapsed = elapsed;
}

我无法编译：

/home/user/dev/MyThread.cpp:104:59: error: expected ‘;’ before ‘lastElapsed’
     std::chrono::duration_cast<std::chrono::microseconds> lastElapsed;
                                                           ^
/home/user/dev/MyThread.cpp:104:70: error: statement cannot resolve address of overloaded function
     std::chrono::duration_cast<std::chrono::microseconds> lastElapsed;
                                                                      ^
/home/user/dev/MyThread.cpp:114:19: error: ‘lastElapsed’ was not declared in this scope
     if (elapsed > lastElapsed)

如何修复此间隔比较器并相应地设置lastElapsed变量类型？

Answer 1

首先，std::chrono::duration_cast不是类型，它的函数返回持续时间，因此lastElapsed的声明无效。你可以像这样解决它：

auto lastElapsed = std::chrono::duration_cast<std::chrono::microseconds>(end - begin);

基本上使用值0初始化lastElapsed。

然后当你计算elapsed时使用相同的类型：

auto elapsed = std::chrono::duration_cast<std::chrono::microseconds>(end - begin);

不要打扰count()成员函数，直到您需要输出值：

    std::cout << "The slowest execution interval is now at  " << elapsed.count() << " us" << std::endl;

Answer 2

检查一下：

    std::chrono::steady_clock::time_point begin, end;
    std::chrono::microseconds lastElapsed;

    begin = std::chrono::steady_clock::now();

    //... some processing to be measured ...

    end = std::chrono::steady_clock::now();
    auto elapsed = std::chrono::duration_cast<std::chrono::microseconds>(end - begin);

    if (elapsed > lastElapsed)
    {
        std::cout << "The slowest execution interval is now at  " << elapsed.count() << "us" << std::endl;          
    }

    lastElapsed = elapsed;

如何比较两次经过的时间？

2 个答案: