[C/C++11]_[初级]_[实用时间库chrono]

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场景

C++11开始提供了一个实用时间库,相比C的time.h强多了,最明显的是可以精确到纳秒.
vs2010还不支持这个库,所以比较可惜,对于新开发的项目,建议用2015可以使用最新特性.
一般用这个库来转换时间或计算函数执行时间或者CPU指令周期.

例子

#include <iostream>  #include <algorithm>#include <sstream>#include <stdlib.h>  #include <string.h>  #include <string>#include <assert.h>#include <ctype.h>  #include <vector> #include <Windows.h>#include <chrono>#include <iomanip>#include <stdint.h>using namespace std;  class A{public:    int i_;};int64_t Factorial(int gene){    return (gene == 1)?1:gene*Factorial(gene-1);}void TestChrono(){    // 计算函数执行时间.    auto start = std::chrono::steady_clock::now();    std::vector<A*> v;    for (int i = 1; i <= 1000000; ++i)    {        v.push_back(new A());    }    for (auto a : v)    {        delete a;    }    auto end = std::chrono::steady_clock::now();    std::chrono::duration<double> diff = end-start;    std::cout << "=>Time Elapse " << diff.count() << " s" << std::endl;    // 获取过去24小时的时间    std::chrono::system_clock::time_point now = std::chrono::system_clock::now();    std::time_t now_c = std::chrono::system_clock::to_time_t(now - std::chrono::hours(24));    char buf[32];    strftime(buf,32,"%Y-%m-%d %H:%M:%S",std::localtime(&now_c));    std::cout << buf << std::endl;    // time_t t;    // t = time(NULL);    // std::stringstream ss;    // ss << put_time(localtime(&t),"%Y-%m-%d %H:%M:%S");    // std::string str = ss.str();    // std::cout << "str: " << str << std::endl;}int main(int argc, char const *argv[])  {      TestChrono();    return 0;  }

输出

=>Time Elapse 0.35702 s2016-05-29 14:26:52

参考

chrono
time_point
put_time

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