将可变大小的字符串C数组编组为C#（Unity iOS）

huangapple
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英文:

Marshalling variable-sized string C array into C# (Unity iOS)

问题

我需要将Objective-C中的字符串集合返回给C#，但我无法理解如何正确地完成这个任务。当我在托管端打印返回的指针时，它的值为0。

Objective-C部分代码如下：

  1. FOUNDATION_EXPORT int _GetAllKeys(char** pointer)
  2. {
  3.     NSArray* array = @[@"key1", @"key2"]; // 虚拟字符串
  4.     
  5.     int size = (int)array.count;
  7.     pointer = malloc(size * sizeof(char *));
  8.     
  9.     for (int i = 0; i < size; i++)
  10.     {
  11.         pointer[i] = MakeStringCopy(array[i]);
  12.     }
  13.     return size;
  14. }

C#部分代码如下：

  1. [DllImport("__Internal")]
  2. private static extern int _GetAllKeys(out IntPtr buffer);
  4. internal static IEnumerable<string> GetAllKeys()
  5. {
  6.     int count = _GetAllKeys(out var buffer);
  7.     List<string> keys = new List<string>();
  8.     for (int i = 0; i < count; i++)
  9.     {
  10.         keys.Add(Marshal.PtrToStringUTF8(IntPtr.Add(buffer, IntPtr.Size))); // 最终当我解决这个问题时，字符串将以UTF8返回，但现在它甚至没有到达这一行，所以忽略编码。
  11.     }
  13.     return keys;
  14. }

---------------- 解决方案 ----------------

Objective-C部分代码如下：

  1. FOUNDATION_EXPORT int _GetAllKeys(char*** pointer)
  2. {
  3.     NSArray* array = @[@"key1", @"key2"];  
  4.     int size = (int)array.count;
  5.     
  6.     *pointer = malloc(size * sizeof(char *));
  8.     for (int i = 0; i < size; i++)
  9.     {
  10.         (*pointer)[i] = MakeStringCopy(array[i]);
  11.     }
  12.     
  13.     return size;
  14. }

C#部分代码如下：

  1. [DllImport("__Internal")]
  2. private static extern int _GetAllKeys(out IntPtr buffer);
  4. internal static IEnumerable<string> GetAllKeys()
  5. {
  6.     int count = _GetAllKeys(out var buffer);
  7.     List<string> keys = new List<string>();
  8.     for (int i = 0; i < count; i++)
  9.     {
  10.         IntPtr ptr = Marshal.ReadIntPtr(buffer);
  11.         keys.Add(Marshal.PtrToStringAuto(ptr));
  12.         buffer = IntPtr.Add(buffer, IntPtr.Size);
  13.     }
  15.     return keys;
  16. }
英文:

I need to return a collection of strings from Objective-C to C# and can't wrap my head around how to do this properly. When I print the returned pointer on managed side its value is 0.

Objective-c

  1. FOUNDATION_EXPORT int _GetAllKeys(char** pointer)
  2. {
  3.     NSArray* array = @[@&quot;key1&quot;, @&quot;key2&quot;]; // dummy strings
  4.     
  5.     int size = (int)array.count;
  7.     pointer = malloc(size * sizeof(char *));
  8.     
  9.     for (int i = 0; i &lt; size; i++)
  10.     {
  11.         pointer[i] = MakeStringCopy(array[i]);
  12.     }
  13.     return size;
  14. }

C#

  1. [DllImport(&quot;__Internal&quot;)]
  2. private static extern int _GetAllKeys(out IntPtr buffer);
  4. internal static IEnumerable&lt;string&gt; GetAllKeys()
  5. {
  6.     int count = _GetAllKeys(out var buffer);
  7.     List&lt;string&gt; keys = new List&lt;string&gt;();
  8.     for (int i = 0; i &lt; count; i++)
  9.     {
  10. 	keys.Add(Marshal.PtrToStringUTF8(IntPtr.Add(buffer, IntPtr.Size))); //eventually when i make this work the strings will be returned as UTF8 but for now its not even making it to this line, so ignore the encoding.
  11.     }
  13.     return keys;
  14. }

---------------- SOLUTION ----------------

Objective-c

  1. FOUNDATION_EXPORT int _GetAllKeys(char*** pointer)
  2. {
  3.     NSArray* array = @[@&quot;key1&quot;, @&quot;key2&quot;];  
  4.     int size = (int)array.count;
  5.     
  6.     *pointer = malloc(size * sizeof(char *));
  8.     for (int i = 0; i &lt; size; i++)
  9.     {
  10.         (*pointer)[i] = MakeStringCopy(array[i]);
  11.     }
  12.     
  13.     return size;
  14. }

C#

  1. [DllImport(&quot;__Internal&quot;)]
  2. private static extern int _GetAllKeys(out IntPtr buffer);
  4. internal static IEnumerable&lt;string&gt; GetAllKeys()
  5. {
  6. 	int count = _GetAllKeys(out var buffer);
  7. 	List&lt;string&gt; keys = new List&lt;string&gt;();
  8. 	for (int i = 0; i &lt; count; i++)
  9. 	{
  10. 		IntPtr ptr = Marshal.ReadIntPtr(buffer);
  11. 		keys.Add(Marshal.PtrToStringAuto(ptr));
  12. 		buffer = IntPtr.Add(buffer, IntPtr.Size);
  13. 	}
  15. 	return keys;
  16. }

答案1

得分: 1

你正在尝试返回一个char**，所以C函数的参数需要是char***：

  1. FOUNDATION_EXPORT int _GetAllKeys(char*** pointer)
  2. {
  3.    NSArray* array = @[@"key1", @"key2"]; // dummy strings
  4.    int size = (int)array.count;
  6.    *pointer = malloc(size * sizeof(char *));
  7.     
  8.    for (int i = 0; i < size; i++)
  9.    {
  10.        (*pointer)[i] = MakeStringCopy(array[i]);
  11.    }
  12.    return size;
  13. }

C#代码看起来没问题，只是IntPtr.Add返回一个新的IntPtr，所以它应该是：

  1. keys.Add(Marshal.PtrToStringUTF8(buffer));
  2. buffer = IntPtr.Add(buffer, IntPtr.Size);
英文:

You are trying to return a char**, so the C function parameter needs to be a char***:

  1. FOUNDATION_EXPORT int _GetAllKeys(char*** pointer)
  2. {
  3.    NSArray* array = @[@&quot;key1&quot;, @&quot;key2&quot;]; // dummy strings
  4.    int size = (int)array.count;
  6.    *pointer = malloc(size * sizeof(char *));
  8.    for (int i = 0; i &lt; size; i++)
  9.    {
  10.        (*pointer)[i] = MakeStringCopy(array[i]);
  11.    }
  12.    return size;
  13. }

The C# code looks fine, except that IntPtr.Add returns a new IntPtr, so it has to be:

  1. keys.Add(Marshal.PtrToStringUTF8(buffer));
  2. buffer = IntPtr.Add(buffer, IntPtr.Size);

huangapple
  • 本文由 发表于 2023年7月27日 17:21:29
  • 转载请务必保留本文链接：https://go.coder-hub.com/76778283.html
  • c#
  • ios
  • marshalling
  • objective-c
  • pointers
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