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