转到由C数组支持的切片 [英] Go slice backed by a C array

问题描述

在Golang Wiki的CGO部分中，有一个解决方案

数组大小 1<<30 ，必须大于或等于 length 变量的任何值.

 程序包主要进口 ("fmt"不安全")func main(){输入YourType字节theCArray:=& [8] YourType {}const arrayLen = 1<<30{长度:= arrayLenfmt.Println()fmt.Println(arrayLen，长度)fmt.Println()slice:=(* [arrayLen] YourType)(unsafe.Pointer(theCArray))[:length:length]fmt.Println(len(slice)，cap(slice)，slice [:8])}{长度:= arrayLen + 1fmt.Println()fmt.Println(arrayLen，长度)fmt.Println()//运行时错误:切片范围超出范围slice:=(* [arrayLen] YourType)(unsafe.Pointer(theCArray))[:length:length]fmt.Println(len(slice)，cap(slice)，slice [:8])}} 

游乐场: https://play.golang.org/p/e4jv8jfU_WI

输出:

 <代码> 1073741824 10737418241073741824 1073741824 [0 0 0 0 0 0 0 0]1073741824 1073741825紧急情况:运行时错误:切片范围超出范围goroutine 1 [运行中]:main.main()/tmp/sandbox576164402/main.go:30 + 0x320 

In the CGO section of the Golang Wiki, there is an article that explains how to create a Go slice backed by a C array. In the article there is a code snipped that details the conversion and most important statement in that snippet is the following:

slice := (*[1 << 30]C.YourType)(unsafe.Pointer(theCArray))[:length:length]

Everything in the statement makes sense to me except the [1 << 30] part. Can you please explain to me why this is needed?

解决方案

The array size, 1 << 30, must be greater than or equal to any value of the length variable.

package main

import (
    "fmt"
    "unsafe"
)

func main() {
    type YourType byte
    theCArray := &[8]YourType{}
    const arrayLen = 1 << 30

    {
        length := arrayLen

        fmt.Println()
        fmt.Println(arrayLen, length)
        fmt.Println()
        slice := (*[arrayLen]YourType)(unsafe.Pointer(theCArray))[:length:length]
        fmt.Println(len(slice), cap(slice), slice[:8])
    }

    {
        length := arrayLen + 1

        fmt.Println()
        fmt.Println(arrayLen, length)
        fmt.Println()
        // runtime error: slice bounds out of range
        slice := (*[arrayLen]YourType)(unsafe.Pointer(theCArray))[:length:length]
        fmt.Println(len(slice), cap(slice), slice[:8])
    }
}

Playground: https://play.golang.org/p/e4jv8jfU_WI

Output:

1073741824 1073741824

1073741824 1073741824 [0 0 0 0 0 0 0 0]

1073741824 1073741825

panic: runtime error: slice bounds out of range

goroutine 1 [running]:
main.main()
    /tmp/sandbox576164402/main.go:30 +0x320

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