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std::chrono::steady_clock:: now

From cppreference.net

C++
Date and time library
std::chrono::steady_clock
Member functions
steady_clock::now
(C++11 起)

返回表示当前时间点的时间点。

返回值

表示当前时间的时间点。

示例

运行此代码 
#include <chrono>
#include <cstddef>
#include <iomanip>
#include <iostream>
#include <numeric>
#include <vector>
volatile int sink; // 防止优化
void do_some_work(std::size_t size)
{
    std::vector<int> v(size, 42);
    sink = std::accumulate(v.begin(), v.end(), 0); // 确保副作用
}
int main()
{
    std::cout << std::fixed << std::setprecision(9) << std::left;
    for (auto size{1ull}; size < 1000'000'000ull; size *= 100)
    {
        const auto start = std::chrono::steady_clock::now();
        do_some_work(size);
        const auto end = std::chrono::steady_clock::now();
        const std::chrono::duration<double> diff = end - start;
        std::cout << "diff = " << diff << "; size = " << size << '\n';
    }
}

可能的输出： 

diff = 0.000005415s; size = 1
diff = 0.000001986s; size = 100
diff = 0.000051633s; size = 10000
diff = 0.006043920s; size = 1000000
diff = 0.636128648s; size = 100000000