Push_back raw pointer as COM pointer? (inputlayout)

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Hi,

I'm struggling with adding 'raw pointers' as CComPtr in a std::vector, without memory leaks.

To illustrate:

- GetInputLayout returns a ID3D11InputLayout* (raw pointer)

- the mInputLayouts is a std::vector<CComPtr<ID3D11InputLayout>>

This code works without memory leaks from D3D (ref counts, no release() issues):

	ID3D11InputLayout *newLayout = mFallbackPack.GetInputLayout(pDevice);
mInputLayouts.emplace_back();
mInputLayouts.back() = newLayout;
ReleaseCOM(newLayout);



When I do it 'directly', I get REF count issues with D3D (leaks):

	mInputLayouts.push_back(mFallbackPack.GetInputLayout(pDevice));


I can explain that the 2nd option gives a leak, because I'm trying to add a RAW pointer in a std::vector with CComPtr's.

Question: is there an easier way to achieve what I want? (without 4 lines of code)

Any input/ thoughts are appreciated.

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Why does GetInputLayout return a raw pointer? Does it AddRef before it returns the object?

For what it's worth, the typical pattern with COM is that returning a pointer is a "weak" pointer, which has not had a reference added to it yet, where a "strong" pointer is returned by out parameter, so you can pass in the address of a CComPtr. Consider making GetInputLayout behave this way. Then you can do:

mInputLayouts.push_back();
mFallbackPack.GetInputLayout(pDevice, &mInputLayouts.back());


If you're on C++17, it looks emplace_back returns a reference, so you could just do:

mFallbackPack.GetInputLayout(pDevice, &mInputLayouts.emplace_back());

Or if you make mFallbackPack return a CComPtr or CComPtr&, then you don't need to manually ReleaseCOM.

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Oh, and there's also the Attach method which doesn't AddRef while taking ownership. So if you still want to return a raw "strong" pointer, you can do:

mInputLayouts.emplace_back(CComPtr<ID3D11InputLayout>().Attach(mFallbackPack.GetInputLayout(pDevice)));
Edited by Jesse Natalie

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I'd say both code snippets you provided should do the same eventually.

newLayout will be released at least twice, once with the direct call and once after it is destructed/overwritten in the vector.

How about GetInputLayout() simply keeps and returns a ComPtr itself? This way its also clear who should perform the cleaning.

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Thanks both. I've been trying out the different options.

But without having GetInputLayout return a CComPtr I could find a way that worked by assigning it directly, like this:

mInputLayouts.emplace_back(CComPtr<ID3D11InputLayout>().Attach(mFallbackPack.GetInputLayout(pDevice)));


This gives the following compiler error:

>e:\projects\crealysm11\crealysm11\d3drenderer\cd3dshadermanager.cpp(176): error C2672: 'std::vector<ATL::CComPtr<ID3D11InputLayout>,std::allocator<_Ty>>::emplace_back': no matching overloaded function found
1>          with
1>          [
1>              _Ty=ATL::CComPtr<ID3D11InputLayout>
1>          ]
1>e:\projects\crealysm11\crealysm11\d3drenderer\cd3dshadermanager.cpp(176): error C2893: Failed to specialize function template 'void std::vector<ATL::CComPtr<ID3D11InputLayout>,std::allocator<_Ty>>::emplace_back(_Valty &&...)'
1>          with
1>          [
1>              _Ty=ATL::CComPtr<ID3D11InputLayout>
1>          ]
1>  e:\projects\crealysm11\crealysm11\d3drenderer\cd3dshadermanager.cpp(176): note: With the following template arguments:


Since I'm not aiming/ using C++ 17, I think I have 3 options:

- with the extra step in the middle, which I already got working

- let the GetInputLayout function return a CComPtr

- add an 'out' parameter for the hard pointer, and pass it like reference (like mentioned above).

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Darn, Attach() doesn't return the CComPtr& like I thought it did. That'd have to be two lines then. You can push_back(), and then do back().Attach().

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N.p., I've decided to let the GetInputLayout function return a CComPtr, and it works like a charm without leaks.

I also decided to keep to the following guideline;

- if I retrieve a pointer from a class, which is a member of the class, then I return a const mObject const pointer

- when a class member function returns a 'local pointer'/ no member, like the GetInputLayout, I return a CComPtr, to prevent leaks and issues on ownership

(which occured in the initial approach, because the ownership of the raw pointer returned by the GetInputLayout function, was unclear, because I added it to a CComPtr vector).