IMultiQI::QueryMultipleInterfaces method (objidlbase.h)

Article
08/19/2022

Retrieves pointers to multiple supported interfaces on an object.

Calling this method is equivalent to issuing a series of separate QueryInterface calls except that you do not incur the overhead of a corresponding number of RPC calls. In multithreaded applications and distributed environments, keeping RPC calls to a minimum is essential for optimal performance.

Syntax

HRESULT QueryMultipleInterfaces(
  [in]      ULONG    cMQIs,
  [in, out] MULTI_QI *pMQIs
);

Parameters

[in] cMQIs

The number of elements in the pMQIs array.

[in, out] pMQIs

An array of MULTI_QI structures. For more information, see Remarks.

Return value

This method can return the following values.

Return code	Description
S_OK	The method retrieved pointers to all requested interfaces.
S_FALSE	The method retrieved pointers to some, but not all, of the requested interfaces.
E_NOINTERFACE	The method retrieved pointers to none of the requested interfaces.

Remarks

The QueryMultipleInterfaces method takes as input an array of MULTI_QI structures. Each structure specifies an interface IID and contains two additional members for receiving an interface pointer and return value.

This method obtains as many requested interface pointers as possible directly from the object proxy. For each interface not implemented on the proxy, the method calls the server to obtain a pointer. Upon receiving an interface pointer from the server, the method builds a corresponding interface proxy and returns its pointer along with pointers to the interfaces it already implements.

Notes to Callers

A caller should begin by querying the object proxy for the IMultiQI interface. If the object proxy returns a pointer to this interface, the caller should then create a MULTI_QI structure for each interface it wants to obtain. Each structure should specify an interface IID and set its pItf member to NULL. Failure to set the pItf member to NULL will cause the object proxy to ignore the structure.

On return, QueryMultipleInterfaces writes the requested interface pointer and a return value into each MULTI_QI structure in the client's array. The pItf member receives the pointer; the hr member receives the return value.

If the value returned from a call to QueryMultipleInterfaces is S_OK, then pointers were returned for all requested interfaces.

If the return value is E_NOINTERFACE, then pointers were returned for none of the requested interfaces. If the return value is S_FALSE, then pointers to one or more requested interfaces were not returned. In this event, the client should check the hr member of each MULTI_QI structure to determine which interfaces were acquired and which were not.

If a client knows ahead of time that it will be using several of an object's interfaces, it can call QueryMultipleInterfaces up front and then, later, if a QueryInterface is done for one of the interfaces already acquired through QueryMultipleInterfaces, no RPC call will be necessary.

On return, the caller should check the hr member of each MULTI_QI structure to determine which interface pointers were and were not returned.

The client is responsible for releasing each of the acquired interfaces by calling Release.

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	objidlbase.h (include ObjIdl.h)

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