在golang中结合时间和日期？

Question

Suppose I have

t := time.Parse("15:04:05.000", "12:16:54.016")

This returns a time.Time which prints out as:

0000-01-01 12:16:54.016 +0000 UTC

But I know what the actual date is and have it stored as a variable called timestamp which is a time.Time struct already. How do I combine them?

e.g. suppose the date is 2019-06-17. I need the output to be:

2019-06-17 12:16:54.016 +0000 UTC

// this doesn't compile
ts.AddDate(timestamp.Year(), timestamp.Month(), timestamp.Day())


cannot use timestamp.Month() (type time.Month) as type int in argument to ts.AddDate 

This should be trivial right? well it is in C which is what I'm most used to. But I haven't found the answer easily for golang. The docs don't tell me the actual underlying field names, just functions. :-/

Answer 1

If you already have the Date in string format, combine the entire date-time into a single string and call time.Parse once:

func datePlusTime(date, timeOfDay string) (time.Time, error) {
    return time.Parse("2006-01-02 15:04:05.000", date+" "+timeOfDay)
}

func main() {
    t, err := datePlusTime("2019-06-17", "12:16:54.016")
    if err != nil {
        panic(err)
    }
    fmt.Println(t)
}

Output:

2019-06-17 12:16:54.016 +0000 UTC

https://play.golang.org/p/kbor6NBMFLl

---

If the date is not in a string format - but you have it in a time.Time, simply coerce to the desired string format, like so:

mydate.Format("2006-01-02") // e.g. mydate:= time.Now()