通过结构指针定义结构

Question

I can't understand why after defining a struct (sp) with a struct pointer (&s), the initial struct (s) keeps being modified while mutating the latter (sp).

http://play.golang.org/p/TdcL_QJqfB

type person struct {
    name string
    age int
}

func main() {
    s := person{name: "Sean", age: 50}
    fmt.Printf("%p : %g
", &s, s.age)

    sp := &s
    fmt.Printf("%p : %g
", &sp, sp.age)

    sp.age = 51
    fmt.Printf("%p : %g
", &sp, sp.age) // yield 51
    fmt.Printf("%p : %g
", &s, s.age) // yields 51, but why not 50 ???
}

Output:

0xc0100360a0 : %!g(int=50)
0xc010000000 : %!g(int=50)
0xc010000000 : %!g(int=51)
0xc0100360a0 : %!g(int=51) // why not 50 ???

I'm new to C family language, Go and pointers, so any pointer ( :) ) to the right concept or error would be very kind of you. thanks in advance !

Answer 1

You have an object s. And a pointer sp that points to s. So when you set age through sp, you're actually modifying s.

Remember, sp is not a separate object. It's like an alias.