Why AddStream last argument is IntPtr, not out uint?

[oven425]

IMFCaptureSink::AddStream last argumnt define out uint, and easy use more

HRESULT AddStream(/* [annotation][in] _In_ */ uint dwSourceStreamIndex, /* [annotation][in] _In_ */ IMFMediaType pMediaType, /* [annotation][in] _In_opt_ */ IMFAttributes pAttributes, /* (DWORD) */ out uint pdwSinkStreamIndex);

[smourier]

Hi,

It's because the parameter is defined in the SDK headers mfcaptureengine.h as optional:

IMFCaptureSink : public IUnknown
{
  ...

    virtual HRESULT STDMETHODCALLTYPE AddStream( 
        /* [annotation][in] */ 
        _In_  DWORD dwSourceStreamIndex,
        /* [annotation][in] */ 
        _In_  IMFMediaType *pMediaType,
        /* [annotation][in] */ 
        _In_opt_  IMFAttributes *pAttributes,
        /* [annotation][out] */ 
        _Out_opt_  DWORD *pdwSinkStreamIndex) = 0;

  ...
};

_Out_opt_ means optional parameter https://learn.microsoft.com/en-us/cpp/code-quality/understanding-sal?view=msvc-170#sal-basics so you can pass IntPtr.Zero when you don't need it.

With DirectN, you can use some helper that will allocate and free memory for you like this:

IMFCaptureSink sink ...
using var cm = new ComMemory(Marshal.SizeOf<uint>()); // size will be 4 obviously...
sink.AddStream(0, type, at, cm.Pointer);
// read back from pointer
var index = Marshal.ReadInt32(cm.Pointer);

[oven425]

Although according to msdn's instructions, it is possible to give IntPtr.Zero, but set IntPtr.Zero cause return E_POINTER Invalid pointer error. AddStream founction retrun streamindex is very import for after AddEffect function. so i recommend last agrument change to out uint

[smourier]

Hi,

The code is generated so no, I won't change this, I don't want to start adding too much exceptions to the ~10000 files in the project.

Report the wrong annotation to Microsoft and when they change it will be generated differently.

[oven425]

OK, I got it