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Hi all, I want to use P/Invoke method to call a C++ DLL, the C++ DLL has a callback function which defined as:

typedef long (CALLBACK * readFileData)(unsigned char * data, int length);

My question is how to define the "unsigned char *" parameter in C# ? Does this is correctly?

public delegate Int32 readFileData(byte[] data, Int32 length);

Thanks in advance.
Posted 18-Jun-10 7:09am
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Solution 1

Given the the callback is called readFileData, then either byte[] or StringBuilder should work.
If it wasn't being changed, then byte[] or String should do.
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Solution 2

I just got this following test scenario working correctly:

C++ code

typedef long (CALLBACK * READDATA)(unsigned char * data, int length);
extern "C" __declspec(dllexport)  void __stdcall SomeFunc(READDATA rd)
 unsigned char data[5] = {'a', 'b', 'c', 'd', 'e'};
 rd(data, 5);

C# code

delegate int ReadDataDelegate(IntPtr data, int len);
static extern void SomeFunc(ReadDataDelegate d);
private static void CallNativeWithCallback()
    ReadDataDelegate newCB = new ReadDataDelegate((data, len) => 
        byte[] array = new byte[len];
        Marshal.Copy(data, array, 0, len);
        foreach (byte b in array)
        return 0; 

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