Question

In short, I am wondering if there is an auto_ptr like type for arrays. I know I could roll my own, I’m just making sure that there isn’t already something out there.

I know about vectors as well. however I don’t think I can use them. I am using several of the Windows APIs/SDKs such as the Windows Media SDK, Direct Show API which in order to get back some structures to call a function which takes a pointer and a size twice. The first time passing NULL as the pointer to get back the size of the structure that I have to allocated in order to receive the data I am looking for. For example:

CComQIPtr<IWMMediaProps> pProps(m_pStreamConfig);
DWORD cbType = 0;
WM_MEDIA_TYPE *pType = NULL;

hr = pProps->GetMediaType(NULL, &cbType);
CHECK_HR(hr);

pType = (WM_MEDIA_TYPE*)new BYTE[cbType];   // Would like to use auto_ptr instread
hr = pProps->GetMediaType(pType, &cbType);
CHECK_HR(hr);

// ... do some stuff

delete[] pType;

Since cbType typically comes back bigger than sizeof(WM_MEDIA_TYPE) due to the fact is has a pointer to another structure in it, I can’t just allocate WM_MEDIA_TYPE objects. Is there anything like this out there?

Answer 1

Use

std::vector<BYTE> buffer(cbType);
pType = (WM_MEDIA_TYPE*)&buffer[0];

or since C++11

std::vector<BYTE> buffer(cbType);
pType = (WM_MEDIA_TYPE*)buffer.data();

instead.

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Additional:
If someone is asking if the Vectors are guaranteed to be contiguous the answer is Yes since C++ 03 standard. There is another thread that already discussed it.

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If C++11 is supported by your compiler, unique_ptr can be used for arrays.

unique_ptr<BYTE[]> buffer(new BYTE[cbType]);
pType = (WM_MEDIA_TYPE*)buffer.get();