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std::chrono::system_clock::now

STD：：时间：：系统[医]时钟：：现在

static std::chrono::time_point now(​(since C++11)

返回表示当前时间点的时间点。

参数

%280%29

返回值

表示当前时间的时间点。

例外

noexcept规格：

noexcept

例

二次

#include <iostream>
#include <vector>
#include <numeric>
#include <chrono>
 
volatile int sink;
int main()
{
    for (auto size = 1ull; size < 1000000000ull; size *= 100) {
        // record start time
        auto start = std::chrono::system_clock::now(
        // do some work
        std::vector<int> v(size, 42
        sink = std::accumulate(v.begin(), v.end(), 0u // make sure it's a side effect
        // record end time
        auto end = std::chrono::system_clock::now(
        std::chrono::duration<double> diff = end-start;
        std::cout << "Time to fill and iterate a vector of " 
                  << size << " ints : " << diff.count() << " s\n";
    }
}

二次

可能的产出：

二次

Time to fill and iterate a vector of 1 ints : 2.43e-07 s
Time to fill and iterate a vector of 100 ints : 4.1e-07 s
Time to fill and iterate a vector of 10000 ints : 2.519e-05 s
Time to fill and iterate a vector of 1000000 ints : 0.00207669 s
Time to fill and iterate a vector of 100000000 ints : 0.423087 s

二次

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