检查失败的新
为什么此 ATL/COM 代码检查分配是否成功？我希望通过 CoGetALloc 或某些此类 api 可以看到自定义分配。符合标准的 C++ 运行时应该抛出 std::bad_alloc，但话又说回来，分配器可能确实已被换成了不抛出的 impl。
DDClientData* pNewData = new DDClientData();
if (pNewData==NULL)
return E_OUTOFMEMORY;
why does this ATL/COM code check for successful alloc? I would have expected a custom allocation to be visible through CoGetALloc or some such api. A standards-conforming C++ runtime should be throwing std::bad_alloc, but then again maybe the allocator has indeed been traded out for a non-throwing impl.
DDClientData* pNewData = new DDClientData();
if (pNewData==NULL)
return E_OUTOFMEMORY;
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COM 方法不允许释放异常 - 实现可以引发异常，但必须在异常转义方法并转换为适当的 HRESULT 之前对其进行处理。
上面的代码不会达到预期的效果 - 一旦
new失败，std::bad_alloc就会被抛出，并且不会执行对空指针的检查。该实现必须将new调用包装到try-catch中，或者将整个方法实现包装到try-抓住。 ATL 通常在新调用。COM methods are not allowed to let exceptions out - the implementation can throw exceptions, but it must handle them before they escape the method and translate to an appropriate HRESULT.
The code above will not have desired effect - once
newfailsstd::bad_allocis thrown and the check for a null pointer is not executed. The implementation has to either wrap thenewcall intotry-catchor wrap the whole method implementation intotry-catch. ATL usually uses _ATLTRY-like macros around thenewcall.COM 不使用异常：任何 COM 对象都应该在失败时返回有效的
HRESULT。另外，还有关于在退出时设置返回值的保证，任何符合标准的 COM 对象都必须遵守。由于这些原因，异常在 COM/ATL 中表现不佳，并且在 Microsoft[1] 内部根本不使用，甚至不用于分配。上面显示的代码示例只是反映了该约定。[1] Sez me，一名 MS FTE。 MS 的 COM 组件是在禁用 C++ 异常的情况下编译的。
COM doesn't use exceptions: any COM object is supposed to return a valid
HRESULTon failure. Plus there are guarantees about setting return values on exit, which any conforming COM object has to comply with. For these reasons, exceptions play badly with COM/ATL, and aren't used at all internally at Microsoft[1], not even for allocations. The code sample shown above simply reflects that convention.[1] Sez me, an MS FTE. COM components at MS are compiled with C++ exceptions disabled.