如何将一个Swift字符串数组传递给一个带有char **参数的C函数

I'm trying to interact with an old C terminal app from Swift. I've successfully integrated the source code and bridged the headers from C to Swift. The code compiles and runs from Xcode 6.3 beta. I've renamed the terminal app's main entry point to:

我正在尝试与Swift的旧C终端应用程序进行交互。我已成功集成源代码并将标头从C桥接到Swift。该代码从Xcode 6.3 beta编译并运行。我已将终端应用程序的主要入口点重命名为：

int initialize(int argc, char **argv);

Nevertheless, I'm struggling to pass the arguments from Swift to this C function. My challenge is to convert the arguments in the right format. Typical input from Swift would look like:

然而，我正在努力将Swift中的参数传递给这个C函数。我的挑战是以正确的格式转换参数。 Swift的典型输入看起来像：

let args = ["-c", "1.2.3.4", "-p", "8000"]

I've tried messing with "cStringUsingEncoding(NSUTF8StringEncoding)" and "withUnsafePointer", but no luck so far. Any help is greatly appreciated!

我已经尝试搞乱“cStringUsingEncoding（NSUTF8StringEncoding）”和“withUnsafePointer”，但到目前为止还没有运气。任何帮助是极大的赞赏！

2 个解决方案

#1

The C function

C函数

int initialize(int argc, char **argv);

is mapped to Swift as

映射到Swift as

func initialize(argc: Int32, argv: UnsafeMutablePointer<UnsafeMutablePointer<Int8>>) -> Int32

This is a possible solution:

这是一个可能的解决方案：

let args = ["-c", "1.2.3.4", "-p", "8000"]

// Create [UnsafeMutablePointer<Int8>]:
var cargs = args.map { strdup($0) }
// Call C function:
let result = initialize(Int32(args.count), &cargs)
// Free the duplicated strings:
for ptr in cargs { free(ptr) }

It uses the fact that in strdup($0) the Swift string $0 is automatically converted to a C string, as explained in String value to UnsafePointer<UInt8> function parameter behavior.

它使用strdup（$ 0）中的事实，Swift字符串$ 0自动转换为C字符串，如字符串值到UnsafePointer 函数参数行为中所述。

#2

Building on Martin’s answer, if you find yourself doing this a lot, you could wrap the dup/free part into a function in a similar style to String.withCString:

基于Martin的回答，如果你发现自己做了很多，你可以将dup / free部分包装成一个与String.withCString类似的函数：

import Darwin

func withCStrings
  <R, S: SequenceType where S.Generator.Element == String>
  (strings: S, @noescape body:  (UnsafeBufferPointer<UnsafeMutablePointer<Int8>>) -> R) 
  -> R  {

    let cstrings = map(strings) { strdup($0) } + [nil]

    let result = cstrings.withUnsafeBufferPointer(body)

    for ptr in cstrings { free(ptr) }

    return result
}

let execvargs = ["/usr/bin/say"] + dropFirst(Process.arguments)

let execvresult = withCStrings(execvargs) {
    execv($0[0], $0.baseAddress)
}

#1