golang编程之时间编程

本文转载于：http://blog.chinaunix.net/uid-24774106-id-4006530.html

编程离不开时间，时间管理，严格的说分成两块，一个是当前的时刻，对应的是一个点，还有是一段时间间隔。本文简单的讲讲go的时间相关的编程，比较简单，高手可以一笑而过。

golang对时间的支持，是package time做的事儿，里面有好多的函数，我就不一一举例学习，毕竟这是官方文档干的事情。我们初步的学习下常用的函数。
第一个是UNIX epoch time，确切的说就是自1970-01-01 00：00：00 GMT以来的秒数，不知道如何获取的，可以在shell下执行 date +%s

manu@manu-hacks:~/code/go/self$ date +%s
1385131172

熟悉Linux下C编程的就是time函数的返回值：

#include <time.h>
time_t now = time(NULL);

golang中一个很重要的表征时间的数据类型是Time，基本就是三个成员变量 sec ，nsec，Location，详细意思可以参看注释。

type Time struct {
// sec gives the number of seconds elapsed since
// January 1, year 1 00:00:00 UTC.
sec int64
// nsec specifies a non-negative nanosecond
// offset within the second named by Seconds.
// It must be in the range [0, 999999999].
nsec int32
// loc specifies the Location that should be used to
// determine the minute, hour, month, day, and year
// that correspond to this Time.
// Only the zero Time has a nil Location.
// In that case it is interpreted to mean UTC.
loc *Location
}

OK，如何取到UNIX epoch time.

now := time.Now()

用time package中Now()函数获取到当前的时间信息，Now()函数非常的重要，他是后面一切转换的起始点。从Now()我们获取到了Time，从Time类型我们从容的获取到UNIX epoch time ,自然获取到year ，month ，day，weekday, hour,minute,second,nanosecond.
获取UNIX epoch time：

var epoch_seconds int64 = now.Unix()

获取Year

func (t Time) Year() int
cur_year := now.Year()

获取Month

func (t Time) Month() Month
cur_month := now.Month()
if cur_month == time.November {
...
}

Month是int类型，fmt.Printf("%v") 或者fmt.Println可以打印出November来，同时Month type有String()函数，输出“November”这样的字符串

const (
January Month = 1 + iota
February
March
April
May
June
July
August
September
October
November
December
)

year mon day，这些都可以在Date函数中一并返回：

func (t Time) Date() (year int, month Month, day int)
year,mon,day = now.Date()

获取Hour

1. func (t Time) Hour() int
cur_hour := now.Hour()

Minute可以通过Minute()返回，second可以通过Second()返回。
time还提供了Clock()的同时返回 hour,minute,second = now.Clock().
在C语言中，我们用gmtime_r获取UTC时间，localtime_r获取本地时间，Golang我们也可以做到

#include<stdio.h>
#include<stdlib.h>
#include<time.h>
int main()
{
time_t now = time(NULL);
printf("elapsed %d second since 1970-01-01 00:00:00\n",now);
struct tm now_utc_tm ={0};
if (gmtime_r(&now,&now_utc_tm) != NULL)
{
printf("UTC time is %d-%02d-%02d %02d:%02d:%02d %s\n",
now_utc_tm.tm_year+1900,now_utc_tm.tm_mon,
now_utc_tm.tm_mday,now_utc_tm.tm_hour,
now_utc_tm.tm_min,now_utc_tm.tm_sec,now_utc_tm.tm_zone);
}
struct tm now_local_tm = {0} ;
if(localtime_r(&now,&now_local_tm) != NULL)
{
printf("local time is %d-%02d-%02d %02d:%02d:%02d %s\n",
now_local_tm.tm_year+1900,now_local_tm.tm_mon,
now_local_tm.tm_mday,now_local_tm.tm_hour,
now_local_tm.tm_min, now_local_tm.tm_sec,now_local_tm.tm_zone);
}
return 0;
}

golang的版本是：

package main
import "fmt"
import "time"
func main(){
now := time.Now()
year,mon,day := now.UTC().Date()
hour,min,sec := now.UTC().Clock()
zone,_ := now.UTC().Zone()
fmt.Printf("UTC time is %d-%d-%d %02d:%02d:%02d %s\n",
year,mon,day,hour,min,sec,zone)
year,mon,day = now.Date()
hour,min,sec = now.Clock()
zone,_ = now.Zone()
fmt.Printf("local time is %d-%d-%d %02d:%02d:%02d %s\n",
year,mon,day,hour,min,sec,zone)
}

输出分别是：

C版本的输出
------------------
UTC time is 2013-10-22 15:49:18 GMT
local time is 2013-10-22 23:49:18 CST
go版本的输出
---------------------
UTC time is 2013-11-22 15:51:22 UTC
local time is 2013-11-22 23:51:22 CST

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我们另一个关心的话题，是时间间隔，比如我们profile一个以非常耗时的function，我们会在函数开始前记下时刻值，函数结束后，再次记录下时刻值，然后两者的差值，就是函数运行时间。
这表明Time是可以相减的，

start_time := time.Now()
expensive_function
end_time :=time.Now()
var duration Duration = end_time.Sub(start_time)

Duration是一种数据类型，其实是个int64类型，表征的是两个时刻之间的纳秒数。

type Duration int64
const (
Nanosecond Duration = 1
Microsecond = 1000 * Nanosecond
Millisecond = 1000 * Microsecond
Second = 1000 * Millisecond
Minute = 60 * Second
Hour = 60 * Minute
)

Duration类型有Minutes()/Second()/Nanoseconds(), 将duration折算成分钟/秒/纳秒。

now := time.Now()
time.Sleep(3*time.Second);
end_time := time.Now()
var dur_time time.Duration = end_time.Sub(now)
var elapsed_min float64 = dur_time.Minutes()
var elapsed_sec float64 = dur_time.Seconds()
var elapsed_nano int64 = dur_time.Nanoseconds()
fmt.Printf("elasped %f minutes or \nelapsed %f seconds or \nelapsed %d nanoseconds\n",
elapsed_min,elapsed_sec,elapsed_nano)

输出如下：

elasped 0.050005 minutes or
elapsed 3.000292 seconds or
elapsed 3000292435 nanoseconds

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第二部分描述Duration明显用到了Sleep()函数，这个函数是以纳秒为单位的，相当于C语言中的nanosleep（）