golang指標的使用,類似C語言
阿新 • • 發佈：2019-01-21
src\model\model.go
package model
import "strconv"
type User struct {
username string
password string
age int32
}
func (this *User) String() string {
return "username: " + this.username + " password: " + this.password + " age:" + strconv.Itoa(int(this.age))
}
注意,User的所有屬性都是私有的
當我們建立 u := &User{}的時候,有沒有辦法將其屬性賦值?
src\main\main.go
package main import ( "fmt" . "model" "unsafe" "reflect" ) //type SliceHeader struct { // Data uintptr // Len int // Cap int //} func main() { var size int var str string size = int(unsafe.Sizeof(str)) fmt.Println(size) // 16 u := &User{} // User的所有成員變數都是private fmt.Println("u :", u) size= int(unsafe.Sizeof(*u)) fmt.Println(size) // 可以將其理解為，指想固定地址，並有長度的[]byte header := &reflect.SliceHeader { Data : uintptr(unsafe.Pointer(u)), Len : size, Cap : size, } b := *(*[]byte)(unsafe.Pointer(header)) println(len(b)) //12 fmt.Println(b) //[0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0] age := 27 size = int(unsafe.Sizeof(&age)) header = &reflect.SliceHeader { Data : uintptr(unsafe.Pointer(&age)), Len : size, Cap : size, } b2 := *(*[]byte)(unsafe.Pointer(header)) fmt.Println(b2) b[16 + 16] = b2[0] b[16 + 16 + 1] = b2[1] b[16 + 16 + 2] = b2[2] b[16 + 16 + 3] = b2[3] b[16 + 16 + 4] = b2[4] b[16 + 16 + 5] = b2[5] b[16 + 16 + 5] = b2[6] b[16 + 16 + 7] = b2[7] fmt.Println(b) fmt.Println("u :", u) }
進入src同級目錄
export GOPATH=`pwd`
go install main
./bin/main
輸出
16
u : username: password: age:0
40
40
[0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0]
[27 0 0 0 0 0 0 0]
[0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 27 0 0 0 0 0 0 0]
u : username: password: age:27
不建議,修改string屬性,如果非要修改,建議將User中的username和password string型別,修改為 [32]byte.
理解思路同,C語言.尤其是C++中對共享記憶體資料的處理.