英文:
Subtracting time.Duration from time in Go
问题
我有一个从time.Now()获取的time.Time值，我想得到一个正好是一个月前的时间。
我知道可以使用time.Sub()进行减法运算（需要另一个time.Time值），但这将得到一个time.Duration类型的结果，而我需要得到一个时间值。
英文:
I have a time.Time value obtained from time.Now() and I want to get another time which is exactly 1 month ago.
I know subtracting is possible with time.Sub() (which wants another time.Time), but that will result in a time.Duration and I need it the other way around.
答案1
得分: 209
根据Thomas Browne的评论，因为lnmx的答案只适用于从日期中减去日期，所以这里是对他的代码进行修改，可以从time.Time类型中减去时间。
package main
import (
"fmt"
"time"
)
func main() {
now := time.Now()
fmt.Println("now:", now)
count := 10
then := now.Add(time.Duration(-count) * time.Minute)
// 如果我们要减去固定数量的单位，可以使用下面的一行代码代替上面的两行代码。它会自动进行类型转换。
// then := now.Add(-10 * time.Minute)
fmt.Println("10 minutes ago:", then)
}
输出结果为：
now: 2009-11-10 23:00:00 +0000 UTC
10 minutes ago: 2009-11-10 22:50:00 +0000 UTC
此外，根据需要，您还可以使用time.Hour或time.Second代替time.Minute。
英文:
In response to Thomas Browne's comment, because lnmx's answer only works for subtracting a date, here is a modification of his code that works for subtracting time from a time.Time type.
package main
import (
"fmt"
"time"
)
func main() {
now := time.Now()
fmt.Println("now:", now)
count := 10
then := now.Add(time.Duration(-count) * time.Minute)
// if we had fix number of units to subtract, we can use following line instead fo above 2 lines. It does type convertion automatically.
// then := now.Add(-10 * time.Minute)
fmt.Println("10 minutes ago:", then)
}
Produces:
now: 2009-11-10 23:00:00 +0000 UTC
10 minutes ago: 2009-11-10 22:50:00 +0000 UTC
Not to mention, you can also use time.Hour or time.Second instead of time.Minute as per your needs.
Playground: https://play.golang.org/p/DzzH4SA3izp
答案2
得分: 171
尝试使用AddDate函数：
package main
import (
"fmt"
"time"
)
func main() {
now := time.Now()
fmt.Println("now:", now)
then := now.AddDate(0, -1, 0)
fmt.Println("then:", then)
}
输出结果为：
now: 2009-11-10 23:00:00 +0000 UTC
then: 2009-10-10 23:00:00 +0000 UTC
Playground链接：http://play.golang.org/p/QChq02kisT
英文:
Try AddDate:
package main
import (
"fmt"
"time"
)
func main() {
now := time.Now()
fmt.Println("now:", now)
then := now.AddDate(0, -1, 0)
fmt.Println("then:", then)
}
Produces:
now: 2009-11-10 23:00:00 +0000 UTC
then: 2009-10-10 23:00:00 +0000 UTC
Playground: http://play.golang.org/p/QChq02kisT
答案3
得分: 75
你可以对 time.Duration 进行否定操作：
then := now.Add(-dur)
你甚至可以将 time.Duration 与 0 进行比较：
if dur > 0 {
dur = -dur
}
then := now.Add(dur)
你可以在 http://play.golang.org/p/ml7svlL4eW 上看到一个可运行的示例。
英文:
You can negate a time.Duration:
then := now.Add(- dur)
You can even compare a time.Duration against 0:
if dur > 0 {
dur = - dur
}
then := now.Add(dur)
You can see a working example at http://play.golang.org/p/ml7svlL4eW
答案4
得分: 4
有一个time.ParseDuration函数可以接受负数的持续时间，具体请参考官方文档。换句话说，如果你可以直接得到一个准确的持续时间，就没有必要对持续时间取反。
例如，当你需要减去一个小时半的时间时，可以这样做：
package main
import (
"fmt"
"time"
)
func main() {
now := time.Now()
fmt.Println("now:", now)
duration, _ := time.ParseDuration("-1.5h")
then := now.Add(duration)
fmt.Println("then:", then)
}
https://play.golang.org/p/63p-T9uFcZo
英文:
There's time.ParseDuration which will happily accept negative durations, as per manual. Otherwise put, there's no need to negate a duration where you can get an exact duration in the first place.
E.g. when you need to substract an hour and a half, you can do that like so:
package main
import (
"fmt"
"time"
)
func main() {
now := time.Now()
fmt.Println("now:", now)
duration, _ := time.ParseDuration("-1.5h")
then := now.Add(duration)
fmt.Println("then:", then)
}
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