Why Does std::chrono::high_resolution_clock Report Lower Resolution Than Expected in Visual Studio 2012?

Resolution Discrepancy in std::chrono::high_resolution_clock

In a test program designed to measure the time taken by std::cout, the output reveals a consistently high deviation from the expected 100 nanosecond resolution of std::chrono::high_resolution_clock. Instead, the measured duration ranges from 1 to 2 microseconds. This discrepancy raises questions about the reported resolution and the accuracy of the time measurement method.

Factors Affecting Resolution

The resolution of a clock, as reported by its period, is the smallest unit of time it can measure. While Visual Studio 2012 includes a high-resolution clock, it unfortunately falls short in precision, typically exhibiting a resolution of around 1 millisecond. This is attributed to the fact that Visual Studio 2012 redefines high_resolution_clock to system_clock, which inherently has lower precision.

Alternative High-Resolution Clock for Visual Studio 2012

To address this limitation, a more accurate high-resolution clock can be implemented using the QueryPerformanceCounter function provided by the operating system. The HighResClock class provided below addresses this issue by utilizing QueryPerformanceCounter to offer a reliable clock with microsecond-level precision:

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()
    {
        LARGE_INTEGER count;
        QueryPerformanceCounter(&amp;count);
        return time_point(duration(count.QuadPart * static_cast<rep>(period::den) / g_Frequency));
    }
};

namespace
{
    const long long g_Frequency = []() -> long long
    {
        LARGE_INTEGER frequency;
        QueryPerformanceFrequency(&amp;frequency);
        return frequency.QuadPart;
    }();
}

This alternative clock can be seamlessly integrated into existing code, allowing high-resolution time measurement even within the constraints of Visual Studio 2012.

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