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COM

COM is the Component Object Model, thus, everything in COM revolves around COM objects.

Registry

Some relevant registry keys for COM are:

HKCR\AppID
HKCR\<ProgId>
HKCR\CLSID (where the CLSIDs are stored)
HKCR\Interface

Reserved/Well known DISPIDs

Four DISPIDs are reserved:

DISPID_VALUE (0): This DISPID is used to identify an object's default member.
DISPID_UNKNOWN (-1): Must be returned by GetIDsOfNames to indicate that a member is not found.
DISPID_PROPERTYPUT (-3)
DISPID_NEWENUM (-4): The _NewEnum method

Apparently, in VBA classes, a method can be decorated with the attribute … vb_userMemId construct to assign predefined disp ids to such a member.

Running Object Table

The Running Object Table (ROT) is a look-up table that keeps track of (registered?) objects. These are identified by a moniker. The form of the entries is (pmkObjectName, pUnkObject). pmkObjectName is a pointer to the moniker.

The goal of the ROT is that a client can bind a moniker to an already running object instead of creating a new object.

A registered(!) object can be looked up in C with the WinAPI function GetActiveObject() and in Visual Basic for Application with GetObject().

An Office application does not register itself right after starting to optimize the startup process. Instead, the registration only takes place when the application looses focus.

In .NET, a COM Object can be located in the ROT with the GetActiveObject() method in System.Runtime.InteropServices.Marshal.

HRESULT

Common HRESULT values include

Value	Name	Description
`0x00000000`	`S_OK`	Operation successful
`0x80004001`	`E_NOTIMPL`	Not implemented
`0x80004002`	`E_NOINTERFACE`	No such interface supported
`0x80004003`	`E_POINTER`	Pointer that is not valid
`0x80004004`	`E_ABORT`	Operation aborted
`0x80004005`	`E_FAIL`	Unspecified failure
`0x8000FFFF`	`E_UNEXPECTED`	Unexpected failure
`0x80070005`	`E_ACCESSDENIED`	General access denied error
`0x80070006`	`E_HANDLE`	Handle that is not valid
`0x8007000E`	`E_OUTOFMEMORY`	Failed to allocate necessary memory
`0x80070057`	`E_INVALIDARG`	One or more arguments are not valid

See also: the System.Runtime.InteropServicves.COMException class is a wrapper for unrecognized HRESULT values.

TODO

COM in plain C (CodeProject). Part 2, 3, 4, 5, 6, 7 and 8.

http://progtutorials.tripod.com/COM.htm

OLE relatated technologies

COM	The fundamental object model: `IUnknown`, `IClassFactor` etc.
DCOM	Distributed (remoting) COM: IDL, NDR pickling, the SCM etc.
Automation	`IDispatch`, `VARIANT`, type libraries etc. (Sometimes also referred to as OLE Automation although it has nothing to do with OLE!)
Active/X	Specification/protocles for «controls» and their containers

Links

ComPower is a PowerShell module to work with COM.

Microsoft: COM Fundamentals

The PowerShell module COM

Index