IVssExamineWriterMetadata的C++与COM接口区别？是否违反COM设计规则？

Great question — this is one of those confusing documentation inconsistencies that pops up with Windows APIs from time to time. Let’s break this down clearly:

1. The Documentation is Wrong (or Misleading) #

First things first: IVssExamineWriterMetadata is absolutely a standard COM interface, despite what the Microsoft Docs page claims. The "non-COM" label is almost certainly a documentation error or misstatement. Here’s the proof:

• Header file definition: It inherits directly from IUnknown, the foundational interface for all COM objects. Its declaration includes the standard COM interface structure, with QueryInterface, AddRef, and Release as the first three methods—all mandatory for COM compliance.
• Real-world code usage: Every sample implementation you referenced treats it as a COM interface:
  • It’s retrieved via COM methods (e.g., IVssBackupComponents::GetWriterMetadata returns a pointer to this interface)
  • Developers use standard COM practices: calling AddRef/Release for reference counting, QueryInterface to cast to other interfaces, and relying on COM’s memory management rules.

2. Why Might the Docs Say "Non-COM"? #

It’s likely a mix-up with how VSS categorizes its interfaces. VSS has two main sets of interfaces: those for requestors (backup apps) and those for writers (apps that participate in backups). Some early VSS documentation might have tried to draw a distinction between these groups, but that doesn’t make them non-COM. All VSS core interfaces are COM-based—this is the only way they can work across process boundaries, which is critical for VSS’s cross-application backup coordination.

3. Does It Violate COM Interface Design Rules? #

No, not at all. IVssExamineWriterMetadata fully adheres to COM’s core design rules:

• It inherits from IUnknown
• It has a unique interface ID (IID_IVssExamineWriterMetadata)
• All methods use the standard COM calling convention (stdcall on Windows)
• It follows COM’s reference counting model

The only "violation" here is the incorrect documentation label, not the interface itself.

内容的提问来源于stack exchange，提问作者Martin