在 Linux 中获取自 epoch 以来的秒数
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/14032865/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Get seconds since epoch in Linux
提问by Boris
Is there cross-platform solution to get seconds since epoch, for windows i use
对于我使用的 Windows，是否有跨平台解决方案来获得自纪元以来的秒数
long long NativesGetTimeInSeconds()
{
return time (NULL);
}
But how to get on Linux?
但是如何进入 Linux 呢？
采纳答案by Zeta
You're already using it: std::time(0)(don't forget to #include <ctime>). However, whether std::timeactually returns the time since epoch isn't specified in the standard (C11, referenced by the C++ standard):
您已经在使用它了：（std::time(0)不要忘记#include <ctime>）。但是，std::time标准（C11，由 C++ 标准引用）中未指定是否实际返回自纪元以来的时间：
7.27.2.4 The
timefunctionSynopsis
#include <time.h> time_t time(time_t *timer);Description
The time function determines the current calendar time. The encoding of the value is unspecified.[emphasis mine]
7.27.2.4
time函数概要
#include <time.h> time_t time(time_t *timer);描述
时间功能确定当前日历时间。 未指定值的编码。[强调我的]
For C++, C++11 and later provide time_since_epoch. However, only in C++20 and later the epoch of std::chrono::system_clockwas specified to be Unix Time, and it is unspecified and therefore possibly non-portable in previous standards.
对于 C++，C++11 及更高版本提供time_since_epoch. 然而，只有在 C++20 和更高版本中， 的时代std::chrono::system_clock才被指定为 Unix 时间，并且它是未指定的，因此在以前的标准中可能是不可移植的。
Still, on Linux the std::chrono::system_clockwill usually use Unix Time even in C++11, C++14 and C++17, so you can use the following code:
尽管如此，在 Linux 上，std::chrono::system_clock即使在 C++11、C++14 和 C++17 中，通常也会使用 Unix Time，因此您可以使用以下代码：
#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();
}
回答by Mats Petersson
The native Linux function for getting time is gettimeofday()[there are some other flavours too], but that gets you the time in seconds and nanoseconds, which is more than you need, so I would suggest that you continue to use time(). [Of course, time()is implemented by calling gettimeofday()somewhere down the line - but I don't see the benefit of having two different pieces of code that does exactly the same thing - and if you wanted that, you'd be using GetSystemTime()or some such on Windows [not sure that's the right name, it's been a while since I programmed on Windows]
用于获取时间的本机 Linux 函数是gettimeofday()[还有其他一些风格]，但这可以为您提供以秒和纳秒为单位的时间，这超出了您的需要，因此我建议您继续使用time(). [当然，time()是通过调用gettimeofday()某处来实现的- 但我没有看到让两段不同的代码做完全相同的事情的好处 - 如果你想要那样，你会使用GetSystemTime()或类似的Windows [不确定那是正确的名字，我已经有一段时间没有在 Windows 上编程了]
回答by Quentin Perez
In C.
在 C.
time(NULL);
In C++.
在 C++ 中。
std::time(0);
And the return value of time is : time_tnot long long
而时间的返回值为：time_tnot long long
