如何使用_com_ptr_t？ [英] How do I use _com_ptr_t?

问题描述

说我有一个拥有 D3DDevice 的课程：

Say I have a class that owns a D3DDevice:

class Thing
{
public:
    Thing()
    {
        D3D11CreateDevice(..., &device, ...);
    }
    ~Thing()
    {
        device->Release();
    }
private:
    ID3D11Device* device;
};

根据我的理解，我可以使用 _com_ptr_t 以确保对象被删除，而不必在析构函数中显式调用 Release（）。问题是，我不能弄清楚模板的正确语法。

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.

我几乎找不到任何关于 _com_ptr_t ，我能找到的最接近的答案是这个（日语）一个。按照语法，我得到一堆编译器错误：

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

顺便说一句，我可以使用它从函数返回COM指针，并确保它们在离开调用者范围时被删除，是吗？

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?

推荐答案

通常有两种方式来处理COM智能指针，我会推荐：

There are usually two ways of dealing with COM smart pointers that I would recommend:

1）你可以#import相应的类型库，它将基于_com_ptr_t自动生成智能指针类型。

1) You can #import the appropriate type library, which will auto generate smart pointer types based on _com_ptr_t.

2）你可以使用CComPtr模板在一个智能指针中的原始COM指针，通过自动AddRef / Release调用来处理资源管理，但不会给你很多其他。

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.

因为我是一个小懒，通常我不介意由 #import 自动生成的包装器的隐式开销，我通常使用1）。使用这种方法的一个最大的好处是， #import 机制还生成函数包装器，使COM函数看起来更像正常函数，具有适当的返回类型和翻译 HRESULT 到 _com_error 异常对象。 IMHO，它倾向于改进C ++ COM代码中的控制流。

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.

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