自Linux时代以来获得秒数 [英] Get seconds since epoch in Linux

问题描述

对于我使用的Windows，是否存在跨平台解决方案以获取自时代以来的秒数

Is there cross-platform solution to get seconds since epoch, for windows i use

long long NativesGetTimeInSeconds()
{
    return time (NULL);
}

但是如何在Linux上运行?

But how to get on Linux?

推荐答案

您已经在使用它: :std :: time(0) (不要忘记 #include< ctime> ).但是， std :: time 是否实际返回时间，因为标准中未指定纪元(

You're already using it: std::time(0) (don't forget to #include <ctime>). However, whether std::time actually returns the time since epoch isn't specified in the standard (C11, referenced by the C++ standard):

7.27.2.4 time 函数

简介

#include <time.h>
time_t time(time_t *timer);

说明

时间功能确定当前日历时间. 值的编码未指定. [强调我的]

Description

The time function determines the current calendar time. The encoding of the value is unspecified. [emphasis mine]

对于C ++，C ++ 11和更高版本提供 time_since_epoch .但是，仅在C ++ 20和更高版本中， std :: chrono的纪元::system_clock 被指定为Unix Time，并且未指定，因此在以前的标准中可能不可移植.

For C++, C++11 and later provide time_since_epoch. However, only in C++20 and later the epoch of std::chrono::system_clock was specified to be Unix Time, and it is unspecified and therefore possibly non-portable in previous standards.

仍然，在Linux上，即使在C ++ 11，C ++ 14和C ++ 17中， std :: chrono :: system_clock 通常也将使用Unix Time，因此您可以使用以下代码代码:

Still, on Linux the std::chrono::system_clock will usually use Unix Time even in C++11, C++14 and C++17, so you can use the following code:

#include <chrono>

// make the decltype slightly easier to the eye
using seconds_t = std::chrono::seconds;

// return the same type as seconds.count() below does.
// note: C++14 makes this a lot easier.
decltype(seconds_t().count()) get_seconds_since_epoch()
{
    // get the current time
    const auto now     = std::chrono::system_clock::now();

    // transform the time into a duration since the epoch
    const auto epoch   = now.time_since_epoch();

    // cast the duration into seconds
    const auto seconds = std::chrono::duration_cast<std::chrono::seconds>(epoch);

    // return the number of seconds
    return seconds.count();
}

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