gopl-zh.github.com/vendor/gopl.io/ch13/unsafeptr/main.go

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2015-12-09 07:57:17 +00:00
// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
// See page 357.
// Package unsafeptr demonstrates basic use of unsafe.Pointer.
package main
import (
"fmt"
"unsafe"
)
func main() {
//!+main
var x struct {
a bool
b int16
c []int
}
// equivalent to pb := &x.b
pb := (*int16)(unsafe.Pointer(
uintptr(unsafe.Pointer(&x)) + unsafe.Offsetof(x.b)))
*pb = 42
fmt.Println(x.b) // "42"
//!-main
}
/*
//!+wrong
// NOTE: subtly incorrect!
tmp := uintptr(unsafe.Pointer(&x)) + unsafe.Offsetof(x.b)
pb := (*int16)(unsafe.Pointer(tmp))
*pb = 42
//!-wrong
*/