'withUnsafeBytes' is deprecated warning when passing void* argument to c function in swift 5

Question

我在 swift 中有一个使用外部提供的 c 库解析 FIT 文件的库。解析函数将 a void * data 作为参数。为了调用该函数，我使用 data.withUnsafeBytes( { (ptr: UnsafePointer<UInt8>) in ...} 转换数据以构建 c 函数的参数并且它工作正常。

从 Xcode 升级到 swift 5 后，我现在收到弃用警告

'withUnsafeBytes' 已弃用：使用 withUnsafeBytes<R>(_: (UnsafeRawBufferPointer) throws -> R) rethrows -> R 代替

我不知道如何修复代码以删除已弃用的警告。该代码在 swift 4

中运行良好且没有警告

我试图将闭包中的参数更改为采用 UnsafeRawBufferPointer 而不是 UnsafePointer 但这导致调用函数时出错：Cannot convert 'UnsafeRawBufferPointer' to expected argument type 'UnsafeRawPointer?'

这是一个显示问题的小 swift 文件：

import Foundation

// Create sample data (Typically would be read from a file
let data = Data(repeating: 1, count: 10)

data.withUnsafeBytes( { (ptr : UnsafePointer<UInt8>) in
    // call the c function with the void* argument
    let value = readFITfile(ptr)
    print( value )
})

还有一个示例 c 函数

unsigned readFITfile(const void * data){
    //Silly example to show it works, just returning the value of pointer as int
    //Typically would parse the data and return a structure
    return (unsigned)data;
}

我用上面的代码在这里保存了一个小仓库https://github.com/roznet/swift2c and the full scale project with the parsing of the file is here https://github.com/roznet/fit-sdk-swift

Answer 1

您必须将闭包参数更改为 UnsafeRawBufferPointer，然后取其 baseAdress（这是一个 UnsafeRawPointer?，相当于 void * 的 Swift在 C):

data.withUnsafeBytes( { (ptr : UnsafeRawBufferPointer) in
    let value = readFITfile(ptr.baseAddress)
    // ...
})

Swift 编译器还可以自动推断闭包参数类型：

data.withUnsafeBytes( { ptr in
    let value = readFITfile(ptr.baseAddress)
    // ...
})

有关此问题的详细信息，请参阅 Swift 论坛中的 withUnsafeBytes Data API confusion。

Answer 2

现在要获取 UnsafePointer，您应该这样做

data.withUnsafeBytes { (ptr: UnsafeRawBufferPointer) in
    if let ptrAddress = ptr.baseAddress, ptr.count > 0 {
        let pointer = ptrAddress.assumingMemoryBound(to: UInt8.self) // here you got UnsafePointer<UInt8>
        let value = readFITfile(ptr)
        print( value )
    } else {
        // Here you should provide some error handling if you want ofc
    }
}

'withUnsafeBytes' is deprecated warning when passing void* argument to c function in swift 5

'withUnsafeBytes' is deprecated warning when passing void* argument to c function in swift 5

c

swift

unsafe-pointers