CODEWITHSUNDEEP
c#uwpmarshallingc++-cx
Stef
Stef

Reputation: 325

Sending an array in a UWP app from C# to a C++/Cx dll

I'm working on a UWP project. I want to send an array of position data (currently I'm just sening a float array as a test) from c# to C++ (in order to render a generated mesh in DirectX on top of XAML stuff).

I tried this: Improper marshaling: C# array to a C++ unmanaged array (the accepted answer). But it doesn't work, I'm guessing I'm missing something, but I don't know what. When I try what he suggests, my compiler complains about the CInput struct declared in C++, because it's native, and so it can't be a parameter in a public function. (the function that is called from c#)

(I would have commented on that question, but I don't have that privilege yet.)

This is my code:

in C#:

public struct CInput
{
    public IntPtr array;
}

public VideoView()
{
    InitializeComponent();
    Loaded += OnLoaded;

    float[] test = new float[4];
    CInput input = new CInput();
    input.array = Marshal.AllocHGlobal(Marshal.SizeOf<float>() * test.Length);
    Marshal.Copy(test, 0, input.array, test.Length);
    D3DPanel.CreateMesh(out input, test.Length);
    Marshal.FreeHGlobal(input.array);
}

in C++ (in D3DPanel.h):

struct CInput
{
    float* array;
};

[Windows::Foundation::Metadata::WebHostHidden]
public ref class D3DPanel sealed : public Track3DComponent::DirectXPanelBase
{
public:
    D3DPanel();

    void CreateMesh(CInput points, int length);
}

Can anyone tell me what I'm doing wrong?

EDIT:

I tried the PassArray pattern, as described here, but it gives this error: "Error C4400 'const int': const/volatile qualifiers on this type are not supported"

void CreateMesh(const Array<float>^ points, int length);

And replacing "const Array^" with "Array" gives "syntax error: identifier 'Array'".

Upvotes: 1

Views: 1112

Answers (1)

Jackie
Jackie

Reputation: 2030

You need to modify your code a little bit, as IntelliSense suggests, use

Platform::WriteOnlyArray<float>^

When it's "out" type, and

const Platform::Array<float>^

when it's "in" type. As C++/CX does not support "in/out" type.

I suggest you do the memory allocation in C++/CX, so in your C# code, you can pass in a array directly without worrying about Marshalling.

Upvotes: 1

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