Pass byte array from Unity C# to C++ plugin

Question

I'm trying to pass raw texture data from Texture2D (byte array) to unmanaged C++ code. In C# code array length is about 1,5kk, however in C++ 'sizeof' always returns 8.

C# declaration of native method :

[DllImport("LibName", CallingConvention = CallingConvention.Cdecl)]
static extern IntPtr ProcessData(byte[] data);

C++:

extern "C" {
    __declspec(dllexport) void ProcessData(uint8_t *data) {
        //sizeof(data) is always 8
    }
}

What am I doing wrong? Is there is a way to pass array without additional memory allocation in C++ code?

sizeof(data) tells you the size of the pointer, you cannot deduce the size of the pointed to array from a pointer, you need to pass it separately — UnholySheep
– UnholySheep, Commented Oct 2, 2017 at 14:29

Programmer · Accepted Answer · 2017-10-02 14:47:26Z

Few things you need to do with your current code:

1.You have to send the size of the array to the C++ plugin in another parameter as UnholySheep mentioned.

2.You also have to pin the array before sending it to the C++ side. This is done with the fixed keyword or GCHandle.Alloc function.

3.If the C++ function has a void return type, your C# function should also have the void return type.

Below is a corrected version of your code. No additional memory allocation is performed.

C#:

[DllImport("LibName", CallingConvention = CallingConvention.Cdecl)]
static extern void ProcessData(IntPtr data, int size);

public unsafe void ProcessData(byte[] data, int size)
{
    //Pin Memory
    fixed (byte* p = data)
    {
        ProcessData((IntPtr)p, size);
    }
}

C++:

extern "C" 
{
    __declspec(dllexport) void ProcessData(unsigned char* data, int size) 
    {
        //sizeof(data) is always 8
    }
}

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