我如何使用C日期和时间函数对UNIX? [英] How do I use the C date and time functions on UNIX?
问题描述
乔恩斯基特谈到编程日期和时间的复杂性,在伦敦举行的2009年DevDays。
Jon Skeet spoke of the complexity of programming dates and times at the 2009 DevDays in London.
你能给我在UNIX上介绍了ANSI C的日期/时间函数,并指出了一些更深层次的问题,使用日期和时间时我还应该考虑?
Can you give me an introduction to the ANSI C date/time functions on UNIX and indicate some of the deeper issues I should also consider when using dates and times?
推荐答案
一个日期/时间可以在两种格式:
Terminology
A date/time can be in two formats:
- 日历时间(又名simpletime) - 时间的绝对值一般,因为一些基本的时间,通常被称为协调世界时
- 本地时间(也称为分解时间) - 由年,月,日等,其中考虑到包括夏令时(如果适用)本地时区的组件的日历时间
日期/时间函数和类型在time.h中头文件中声明。
The date/time functions and types are declared in the time.h header file.
时间可以被存储为一个整数或者作为结构的一个实例:
Time can be stored as a whole number or as an instance of a structure:
-
作为使用 time_t的算术类型的一些 - 以日历时间保存为自UNIX纪元经过1970年1月1日的秒数00:00:00
as a number using the time_t arithmetic type – to store calendar time as the number of seconds elapsed since the UNIX epoch January 1, 1970 00:00:00
使用结构的timeval - 存储日历时间从unix新纪元经过1970年1月1日秒和纳秒00:00:00
using the structure timeval – to store calendar time as the number of seconds and nanoseconds elapsed since the UNIX epoch January 1, 1970 00:00:00
使用结构 TM 存储本地时间,它包含了属性,如以下
using the structure tm to store localtime, it contains attributes such as the following:
tm_hour
tm_min
tm_isdst
在上面的tm_isdst属性是用来表示夏令时(DST)。如果该值为正它是DST,如果该值为0它没有DST
The tm_isdst attribute above is used to indicate Daylight Saving Time (DST). If the value is positive it is DST, if the value is 0 it is not DST.
#include <stdio.h>
#include <time.h>
int main ( int argc, char *argv[] )
{
time_t now;
now = time ( NULL );
printf ( "It’s %ld seconds since January 1, 1970 00:00:00", (long) now );
return 0;
}
在功能时间上面的程序读取UNIX系统时间,减去从1970年00:00:00(UNIX新纪元),并在几秒钟内返回其结果。1月1日,
In the program above the function time reads the UNIX system time, subtracts that from January 1, 1970 00:00:00 (the UNIX epoch) and returns its result in seconds.
#include <stdio.h>
#include <time.h>
int main ( int argc, char *argv[] )
{
time_t now;
struct tm *lcltime;
now = time ( NULL );
lcltime = localtime ( &now );
printf ( "The time is %d:%d\n", lcltime->tm_hour, lcltime->tm_min );
return 0;
}
在功能本地时间上面的程序转换的秒数时间从UNIX纪元到分解时间。本地时间读取UNIX环境TZ(通过向tzset函数的调用)相对于时间以返回到时区并设置tm_isdst的属性
In the program above the function localtime converts the elapsed time in seconds from the UNIX epoch into the broken-down time. localtime reads the UNIX environment TZ (through a call to the tzset function) to return the time relative to the timezone and to set the tm_isdst attribute.
在UNIX(使用bash)TZ变量的典型设置情况如下:
A typical setting of the TZ variable in UNIX (using bash) would be as follows:
export TZ=GMT
或
export TZ=US/Eastern
程序打印当前格式化格林威治时间
#include <stdio.h>
#include <time.h>
int main ( int argc, char *argv[] )
{
time_t now;
struct tm *gmt;
char formatted_gmt [50];
now = time ( NULL );
gmt = gmtime ( &now );
strftime ( formatted_gmt, sizeof(formatted_gmt), "%I:%M %p", gmt );
printf ( "The time is %s\n", formatted_gmt );
return 0;
}
在功能的strftime 上面的程序提供了专门的格式日期。
In the program above the function strftime provides specialised formatting of dates.
- Leap seconds
- What should we do to prepare for 2038?
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