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IServiceProviderImpl::QueryService

Creates or accesses the specified service and returns an interface pointer to the specified interface for the service.

STDMETHOD(QueryService)( 
   REFGUID guidService, 
   REFIID riid, 
   void** ppvObject  
);
[IN] guidService

Pointer to a service identifier (SID).

[IN] riid

Identifier of the interface to which the caller is to gain access.

[OUT] ppvObj

Indirect pointer to the requested interface.

The returned HRESULT value is one of the following:

Return value

Meaning

S_OK

The service was successfully created or retrieved.

E_INVALIDARG

One or more of the arguments is invalid.

E_OUTOFMEMORY

Memory is insufficient to create the service.

E_UNEXPECTED

An unknown error occurred.

E_NOINTERFACE

The requested interface is not part of this service, or the service is unknown.

QueryService returns an indirect pointer to the requested interface in the specified service. The caller is responsible for releasing this pointer when it is no longer required.

When you call QueryService, you pass both a service identifier (guidService) and an interface identifier (riid). The guidService specifies the service to which you want access, and the riid identifies an interface that is part of the service. In return, you receive an indirect pointer to the interface.

The object that implements the interface might also implement interfaces that are part of other services. Consider the following:

  • Some of these interfaces might be optional. Not all interfaces defined in the service description are necessarily present on every implementation of the service or on every returned object.

  • Unlike calls to QueryInterface, passing a different service identifier does not necessarily mean that a different Component Object Model (COM) object is returned.

  • The returned object might have additional interfaces that are not part of the definition of the service.

Two different services, such as SID_SMyService and SID_SYourService, can both specify the use of the same interface, even though the implementation of the interface might have nothing in common between the two services. This works, because a call to QueryService (SID_SMyService, IID_IDispatch) can return a different object than QueryService (SID_SYourService, IID_IDispatch). Object identity is not assumed when you specify a different service identifier.

Header: atlcom.h

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