切片和指针的范围

Question

I have the following range over a slice of a specific struct:

var t1, t2 *time.Time
for _, d := range entries {
    if d.EntryType == print {
        t1 = &d.LogTime
    }
    if d.EntryType == saw {
        t2 = &d.LogTime
    }
}

In my example I have two objects in my struct and I know that they are different. But when I Println both Time pointers with String or when I make some calculations, I can see that both have the same value of the second one.

When I change the assignment to

tmp := d.LogTime
t1 = &tmp

i can make my calculations, because both pointers are pointing to different objects.

Answer 1

The application is taking the address of the variable d, not the address of a slice element. The variable d is scoped outside the loop and has the same address on each iteration of the loop.

The code

tmp := d.LogTime
t1 = &tmp

works because tmp is scoped inside the loop.

Perhaps you intended to take the address of the slice element. If so, use this code:

for i:= range entries {
    if d.EntryType == print {
        t1 = &entries[i].LogTime
    }
    if d.EntryType == saw {
        t2 = &entries[i].LogTime
    }
}

There may be a reason to use *time.Time values here, but typically applications work with time.Time. This code may do what you need:

var t1, t2 time.Time
for _, d := range entries {
    if d.EntryType == print {
        t1 = d.LogTime
    }
    if d.EntryType == saw {
        t2 = d.LogTime
    }
}