（* [1 <30] C.YourType）在CGo中做了什么？ [英] What does (*[1 &lt;&lt; 30]C.YourType) do exactly in CGo?

问题描述

在 Golang wiki 中的将C数组转换为Go片下，有一段代码演示了如何创建一个由C数组支持的Go slice。

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]

任何人都可以准确解释（* [1 <30] C.YourType）的含义吗？它如何将一个 unsafe.Pointer 变成一个Go切片？

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

推荐答案

* [1 << 30] C.YourType 本身不做任何事情，它是一种类型。具体来说，它是一个指向大小 1 <<<< 30 ， C.YourType 值。

*[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.

您在第三个表达式是类型转换。
这将 unsafe.Pointer 转换为 * [1<< 30] C.YourType 。

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

然后，您将转换后的数组值，并将其转换为带有完整切片表达式（数组值不需要对切片表达式进行取消引用，所以没有必要以 * 作为前缀，即使它是一个指针）。

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).

您可以扩展它如下所示：

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[0:length:length]

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