配列* CONST *

Question

Iトラブル署名の交流機能のためのアレイにスイフト文字列の配列を変換した午前：スウィフト、CONSTチャー*のCONSTで

PGconn *PQconnectStartParams(const char * const *keywords, const char * const *values, int expand_dbname) 

*次のように機能することを「オプション」と呼ばれ、フィード：[文字列]：だから私は辞書の内容を変換しよう

<UnsafePointer<UnsafePointer<Int8>> 

：としてが現れ

var keys = [[Int8]]() 
var values = [[Int8]]() 
for (key, value) in options { 
    var int8Array = key.cStringUsingEncoding(NSUTF8StringEncoding)! 
    keys.append(int8Array) 
    int8Array = value.cStringUsingEncoding(NSUTF8StringEncoding)! 
      values.append(int8Array) 
} 
pgConnection = PQconnectStartParams(UnsafePointer(keys), UnsafePointer(values), 0) 

コンパイルして実行しますが、機能しません。

洞察力があれば幸いです。

Answer 1

これは完璧ではありませんが、少なくとも動作します。

let options = ["key1": "value1", "key2": "value2", "key3": "value3", "key4": "value4"] 

var keys = [String]() 

for (key, value) in options { 

    keys.append(key) 
} 

//you need to identify how many paramenters should be provided and set them following "static way" 
//I did not find how to prepare this dynamically 
let cKey1 = keys[0].cStringUsingEncoding(String.defaultCStringEncoding())! 
let key1Pointer = UnsafePointer<CChar>(cKey1) 

let cKey2 = keys[1].cStringUsingEncoding(String.defaultCStringEncoding())! 
let key2Pointer = UnsafePointer<CChar>(cKey2) 

let cKey3 = keys[2].cStringUsingEncoding(String.defaultCStringEncoding())! 
let key3Pointer = UnsafePointer<CChar>(cKey3) 

let cKey4 = keys[3].cStringUsingEncoding(String.defaultCStringEncoding())! 
let key4Pointer = UnsafePointer<CChar>(cKey4) 


let keysCArray = [key1Pointer, key2Pointer, key3Pointer, key4Pointer] 

f(keysCArray) 

/* 
C - code 

void f(const char * const *keywords) { 

printf("%s\n", keywords[0]); 
printf("%s\n", keywords[1]); 
printf("%s\n", keywords[2]); 
printf("%s\n", keywords[3]); 

} 
*/ 

希望します。あなたが望むなら私はサンプルアプリケーションを共有することができます。ここで

Answer 2

は、一般的にそれを行いますSwift3のArrayの拡張機能です：

public extension Array { 

    // Translate [String] to (const char * const *), which translates to Swift as 
    public func cStringArray() throws -> ArrayBridge<Element,CChar> { 
     return try ArrayBridge<Element,CChar>(array:self) { 
      guard let item = $0 as? String, 
        let translated = item.cString(using: .utf8) else { 
       fatalError() 
      } 
      return translated 
     } 
    } 
} 

/* 
We need to have this intermediate object around to hold on to the translated objects, otherwise they will go away. 
The UnsafePointer won't hold on to the objects that it's pointing to. 
*/ 
public struct ArrayBridge<SwiftType,CType> { 

    let originals :[SwiftType] 
    let translated :[[CType]] 
    let pointers :[UnsafePointer<CType>?] 
    public let pointer :UnsafePointer<UnsafePointer<CType>?> 

    init(array :[SwiftType], transform: @noescape (SwiftType) throws -> [CType]) throws { 
     self.originals = array 
     self.translated = try array.map(transform) 

     var pointers = [UnsafePointer<CType>?]() 
     for item in translated { 
      pointers.append(UnsafePointer<CType>(item)) 
     } 
     pointers.append(nil) 
     self.pointers = pointers 
     self.pointer = UnsafePointer(self.pointers) 
    } 
} 

その後すぐに[OK]を

try stringArray.cStringArray().pointer