how can i get a object's size

[四月份平民]

If there is a type definition锟斤拷

 

type Example struct {

a byte

b, c int32

        d,e,f float32

        g,h,i, j [1234]byte

        .......

}

what can i do  to get the size of  a object of Example quickily锟斤拷

[peterGo]

package main

import (
"fmt"
"unsafe"
)

type T struct {

a byte
b, c int32
d, e, f float32
g, h, i, j [1234]byte
}

func main() {
size := unsafe.Sizeof(T{})
fmt.Println(size)
}

Output: 4960

Peter

[Kal]

Be careful if your struct contains slices. Sizeof will include the size of the slice data type, not the underlying data ie. flatten the structure like gob encoding will.

[fango]

For those cannot use package unsafe, http://play.golang.org/p/L3q1R2E-QJ
package main
import ("fmt")

type T struct {

a byte
b, c int32
d,e,f float32
g,h,i, j [1234]byte
}

var a [2]T
func main(){
p0 := &a[0]
p1 := &a[1]
s := fmt.Sprintf("%p %p", p1, p0)
var i0, i1 int
fmt.Sscanf(s, "0x%x 0x%x", &i1, &i0)
fmt.Printf("%s = %d\n", s, i1 - i0)
}

[John Asmuth]

That seems unreliable. I don't believe there is a guarantee that the compiler won't pad the data in the array to make it align to something convenient.

[mikespook]

also, the "reflect" package can resolve this. http://play.golang.org/p/p4A_RoA6Gt

package main

import (
    "fmt"

    "reflect"
)

type T struct {

    a byte
    b, c int32
        d,e,f float32
        g,h,i, j [1234]byte   
}

var a T
func main(){
    t := reflect.TypeOf(a)
    fmt.Printf("Sizeof(T) = %d Byte", t.Size())
}