How do I use _com_ptr_t?
c++, com
Solution
There are usually two ways of dealing with COM smart pointers that I would recommend:
1) You can #import the appropriate type library, which will auto generate smart pointer types based on _com_ptr_t.
2) You can use the CComPtr template to wrap your raw COM pointer in a smart pointer that takes care of the resource management via automatic AddRef/Release calls, but doesn't give you much else.
Because I'm a little lazy and normally I don't mind the implicit overhead of the wrapper auto-generated by `#import`, I usually use 1). One of the big benefits of using that approach is that the `#import` mechanism also generates function wrappers that make COM functions look more like normal functions with proper return types and a translation of the `HRESULT` to `_com_error` exception objects. IMHO that tends to improve the control flow in C++ COM code.
Problem
Say I have a class that owns a `D3DDevice`: ``` class Thing { public: Thing() { D3D11CreateDevice(..., &device, ...); } ~Thing() { device->Release(); } private: ID3D11Device* device; }; ``` From what I understand, I can use `_com_ptr_t` to ensure that the object gets deleted without my having to explicitly call `Release()` in the destructor. The problem though is that I can't figure out the correct syntax for the template. I could find hardly any information on `_com_ptr_t`, and the closest thing I could find to an answer was this (Japanese) one. Following the syntax there, I get a bunch of compiler errors: ``` private: //ID3D11Device* device; _com_ptr_t <_com_IIID<ID3D11Device, &__uuidof(ID3D11Device)>> device; error C2143: syntax error : missing ';' before '<' error C4430: missing type specifier - int assumed. Note: C++ does not support default-int error C2238: unexpected token(s) preceding ';' error C2065: 'device' : undeclared identifier ``` By the way, I can use this to return COM pointers from functions and ensure that they get deleted when they leave the caller's scope, right?