是否可以在编译时获取当前时间？

Question

我正在考虑使用当前时间戳作为一个版本。我想在编译时检索该信息。所以理想情况下我想这样做：

constexpr long long currentTimestamp = getCurrentTimestamp();

C++14 可以吗？

Answer 1

使用 standard C __TIME__ 宏和 __DATE__ 宏。有关示例，请参阅 this 问题。

Answer 2

使用__DATE__和__TIME__或__TIMESTAMP__：

#include <stdio.h>

int main()
{
    printf("date: '%s'\n", __DATE__);
    printf("time: '%s'\n", __TIME__);
    printf("timestamp: '%s'\n", __TIMESTAMP__);
}

Output:

date: 'May  5 2017'
time: '00:29:26'
timestamp: 'Fri May  5 00:29:26 2017'

但是，出于显而易见的原因，您需要确保重新编译该文件。

来自 gcc online docs:

__DATE__

This macro expands to a string constant that describes the date on which the preprocessor is being run. The string constant contains eleven characters and looks like "Feb 12 1996". If the day of the month is less than 10, it is padded with a space on the left.

__TIME__

This macro expands to a string constant that describes the time at which the preprocessor is being run. The string constant contains eight characters and looks like "23:59:01".

__TIMESTAMP__

This macro expands to a string constant that describes the date and time of the last modification of the current source file. The string constant contains abbreviated day of the week, month, day of the month, time in hh:mm:ss form, year and looks like "Sun Sep 16 01:03:52 1973". If the day of the month is less than 10, it is padded with a space on the left.

请注意，__TIMESTAMP__ 不是标准的，某些编译器可能不支持它。

是否可以在编译时获取当前时间？

Is it possible to get current time at compile time?

c++

timestamp

constexpr

c++14