CODEWITHSUNDEEP
c#c++
Simon SCHÖNEGGER
Simon SCHÖNEGGER

Reputation: 117

Pass C# Byte[] to C++ API

I have to pass an Byte array containing an MAC-Address to a C++ Method. Since I don't have much experience with working with c C++ APIsI don't know how to do this. I've tried to pass the array itself, but got an invalid parameter code as response from the API. I've also tried to create an IntPtr but to no avail.
I know that the problem is that C++ can't handle managed datatypes such as arrays, so I've to create a unmanaged array somehow, I think.

Here is the definition of the C++ Method:

ll_status_t LL_Connect(
ll_intf_t intf, 
uint8_t address[6]);

The array in C# is defined the following way:

Byte[] addr = new Byte[6];

Of course, the array is not empty.

Upvotes: 4

Views: 4344

Answers (1)

Neargye
Neargye

Reputation: 2108

For example:

C++

extern "C"
{
    __declspec(dllexport) void GetData(uint8_t* data, uint32_t length)
    {
      for (size_t i = 0; i < length; ++i)
        data[i] = i;
    }
}

C#

[DllImport("LibName.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Ansi)]
public static extern void GetData([In, Out] [MarshalAs(UnmanagedType.LPArray)] byte[] data, uint length);

And use in C#

 byte[] data = new byte[4];
 GetData(data, (uint)data.Length);

If you have an array fixed length, for example:

C++

extern "C"
{
    __declspec(dllexport) void GetData(uint8_t data[6])
    {
      for (size_t i = 0; i < 6; ++i)
        data[i] = i;
    }
}

C#

[DllImport("LibName.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Ansi)]
public static extern void GetData([In, Out] [MarshalAs(UnmanagedType.LPArray, SizeConst = 6)] byte[] data);

And use in C#

 byte[] data = new byte[6];
 GetData(data);

For your case:

    [DllImport("LibName.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Ansi)]
    public static extern int LL_Connect(byte intf, [In, Out] [MarshalAs(UnmanagedType.LPArray, SizeConst = 6)] byte[] address);

Upvotes: 6

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