为什么地址大小不同？ （0x206a10-0x104382e0）

Question

http://play.golang.org/p/BgnHN-GikU

var p1 = new(int)
var p2 *int = new(int)
var p3 = 0
var p4 *int

func main() {
    fmt.Println(*p1, &p1, p1)
    fmt.Println()
    fmt.Println(*p2, &p2, p2)
    fmt.Println()
    fmt.Println(p3, &p3)
    fmt.Println()
    fmt.Println(p4, &p4)
}

0 0x206a10 0x104382e0

0 0x206a14 0x104382f0

0 0x21ccc0

<nil> 0x206a18

Answer 1

It's not the address size what is different, it's the size (length) of the hexadecimal representation as you printed it.

All addresses you print on the Go Playground are 4 bytes, but if the first bytes (or bits) are zero, they are not printed.

Also if you take a closer look, addresses of your global vars have 6 hexa digits, pointers allocated and returned by new() have 8 hexa digits. This is because those ints (returned by new()) are allocated on the heap with bigger offset (and thus "bigger" memory address).

For example:

var i, j int32 = 123, 123000
fmt.Printf("%x %x
", i, j)

Prints 7b 1e078 even though both numbers are 4 bytes long (32 bits). You may use a format string to add padding 0s like this:

fmt.Printf("%08x %08x
", i, j)

Which results in 0000007b 0001e078 but this will always pad to 8 digits even if i or j would be "less" than 4 bytes (e.g. int16), so this padding won't tell you if they are of different sizes.