(*[1 << 30]C.YourType) 在 CGo 中究竟做了什么?

问题描述

在 Golang wiki 中的Turning C arrays into Go slices"下，有是一段代码，用于演示如何创建由 C 数组支持的 Go 切片.

导入C"导入不安全"...var theCArray *C.YourType = C.getTheArray()长度 := C.getTheArrayLength()切片 := (*[1 << 30]C.YourType)(unsafe.Pointer(theCArray))[:length:length]

谁能解释一下 (*[1 << 30]C.YourType) 到底是做什么的?它如何将 unsafe.Pointer 变成 Go 切片?

解决方案

*[1 <<30]C.YourType 本身不做任何事情，它是一个类型.具体来说，它是一个指向大小为 1 ，C.YourType 值.大小是任意的，仅表示需要在主机系统上有效的上限.

您在第三个表达式中所做的是类型转换.这会将 unsafe.Pointer 转换为 *[1 <<30]C.YourType.

然后，您将转换后的数组值转换为带有 完整切片的切片表达式(切片表达式不需要取消对数组值的引用，因此即使它是一个指针，也不需要为该值添加前缀*).>

你可以像这样扩展它:

//unsafe.Pointer to the C arrayunsafePtr := unsafe.Pointer(theCArray)//将 unsafePtr 转换为 *[1 <<30]C.你的类型arrayPtr := (*[1 << 30]C.YourType)(unsafePtr)//将数组切片为 Go 切片，具有相同的后备数组//作为CArray，确保指定容量以及//长度.切片 := arrayPtr[:length:length]

In the Golang wiki, under "Turning C arrays into Go slices", there is a block of code that demonstrates how to create a Go slice backed by a C array.

import "C"
import "unsafe"
...
        var theCArray *C.YourType = C.getTheArray()
        length := C.getTheArrayLength()
        slice := (*[1 << 30]C.YourType)(unsafe.Pointer(theCArray))[:length:length]

Can anyone explain exactly what (*[1 << 30]C.YourType) does? How does it turn an unsafe.Pointer into a Go slice?

解决方案

*[1 << 30]C.YourType doesn't do anything itself, it's a type. Specifically, it's a pointer to an array of size 1 << 30, of C.YourType values. The size is arbitrary, and only represents an upper bound that needs to be valid on the host system.

What you're doing in the third expression is a type conversion.This converts the unsafe.Pointer to a *[1 << 30]C.YourType.

Then, you're taking that converted array value, and turning it into a slice with a full slice expression (Array values don't need to be dereferenced for a slice expression, so there is no need to prefix the value with a *, even though it is a pointer).

You could expand this out a bit like so:

// unsafe.Pointer to the C array
unsafePtr := unsafe.Pointer(theCArray)

// convert unsafePtr to a pointer of the type *[1 << 30]C.YourType
arrayPtr := (*[1 << 30]C.YourType)(unsafePtr)

// slice the array into a Go slice, with the same backing array
// as theCArray, making sure to specify the capacity as well as
// the length.
slice := arrayPtr[:length:length]

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