IMarshal::UnmarshalInterface method (objidl.h)

Article
08/19/2022

Unmarshals an interface pointer.

Syntax

HRESULT UnmarshalInterface(
  [in]  IStream *pStm,
  [in]  REFIID  riid,
  [out] void    **ppv
);

Parameters

[in] pStm

A pointer to the stream from which the interface pointer is to be unmarshaled.

[in] riid

A reference to the identifier of the interface to be unmarshaled.

[out] ppv

The address of pointer variable that receives the interface pointer. Upon successful return, *ppv contains the requested interface pointer of the interface to be unmarshaled.

Return value

This method can return the standard return value E_FAIL, as well as the following values.

Return code	Description
S_OK	The interface pointer was unmarshaled successfully.
E_NOINTERFACE	The specified interface is not supported.

Remarks

The COM library in the process where unmarshaling is to occur calls the proxy's implementation of this method.

Notes to Callers

You do not call this method directly. There are, however, some situations in which you might call it indirectly through a call to CoUnmarshalInterface. For example, if you are implementing a stub, your implementation would call CoUnmarshalInterface when the stub receives an interface pointer as a parameter in a method call.

Notes to Implementers

The proxy's implementation should read the data written to the stream by the original object's implementation of IMarshal::MarshalInterface and use that data to initialize the proxy object whose CLSID was returned by the marshaling stub's call to the original object's implementation of IMarshal::GetUnmarshalClass.

To return the appropriate interface pointer, the proxy implementation can simply call QueryInterface on itself, passing the riid and ppv parameters. However, your implementation of UnmarshalInterface is free to create a different object and, if necessary, return a pointer to it.

Just before exiting, even if exiting with an error, your implementation should reposition the seek pointer in the stream immediately after the last byte of data read.

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps \| UWP apps]
Minimum supported server	Windows 2000 Server [desktop apps \| UWP apps]
Target Platform	Windows
Header	objidl.h (include ObjIdl.h)

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