Media Foundation using C instead of C++ - c

Question

I am learning to use the Media Foundation API from sample code shown in Microsoft website using C instead of C++. The sample code is shown below.
HRESULT CreateVideoCaptureDevice(IMFMediaSource **ppSource)
{
*ppSource = NULL;
UINT32 count = 0;
IMFAttributes *pConfig = NULL;
IMFActivate **ppDevices = NULL;
// Create an attribute store to hold the search criteria.
HRESULT hr = MFCreateAttributes(&pConfig, 1);
// Request video capture devices.
if (SUCCEEDED(hr))
{
hr = pConfig->SetGUID(
MF_DEVSOURCE_ATTRIBUTE_SOURCE_TYPE,
MF_DEVSOURCE_ATTRIBUTE_SOURCE_TYPE_VIDCAP_GUID
);
}
// Enumerate the devices,
if (SUCCEEDED(hr))
{
hr = MFEnumDeviceSources(pConfig, &ppDevices, &count);
}
// Create a media source for the first device in the list.
if (SUCCEEDED(hr))
{
if (count > 0)
{
hr = ppDevices[0]->ActivateObject(IID_PPV_ARGS(ppSource));
}
else
{
hr = MF_E_NOT_FOUND;
}
}
for (DWORD i = 0; i < count; i++)
{
ppDevices[i]->Release();
}
CoTaskMemFree(ppDevices);
return hr;
}
When I tried to build the sample code, I always get the following error:
error C2039: 'ActivateObject': is not a member of 'IMFActivate'
error C2039: 'Release': is not a member of 'IMFActivate'
error C2039: 'SetGUID': is not a member of 'IMFAttributes'
I explored the definition of IMFActivate and IMFAttributes (in mfidl.h) and I notice it have a C style interface.
May I know if anyone can show an example of how to use the interface ?

Answer 1

You should be using COM interfaces defined "C style", using virtual method table pointer:
IMFActivate* pMfActivate = ...
IMFMediaSource* pMfMediaSource;
pMfActivate->lpVtbl->ActivateObject(
pMfActivate, &IID_IMFMediaSource, (IUnknown**) &pMfMediaSource);
where C++ style is
IMFActivate* pMfActivate = ...
IMFMediaSource* pMfMediaSource;
pMfActivate->ActivateObject(
__uuidof(IMFMediaSource), (IUnknown**) &pMfMediaSource);