# IPersist

The IPersist interface defines the single method GetClassID, which is designed to supply the CLSID of an object that can be stored persistently in the system. A call to this method can allow the object to specify which object handler to use in the client process, as it is used in the OLE default implementation of marshaling.

IPersist is the base interface for three other interfaces: IPersistStorage, IPersistStream, and IPersistFile. Each of these interfaces, therefore, includes the GetClassID method, and the appropriate one of these three interfaces is implemented on objects that can be serialized to a storage, a stream, or a file. The methods of these interfaces allow the state of these objects to be saved for later instantiations, and load the object using the saved state. Typically, the persistence interfaces are implemented by an embedded or linked object, and are called by the container application or the default object handler

##### When to Implement

You must implement the single method of IPersist in implementing any one of the other persistence interfaces: IPersistStorage, IPersistStream, or IPersistFile. Typically, for example, you would implement IPersistStorage on an embedded object, IPersistFile on a linked object, and IPersistStream on a new moniker class, although their uses are not limited to these objects. You could implement IPersist in a situation where all that is required is to obtain the CLSID of a persistent object, as it is used in marshaling.

##### When to Use

The single method of IPersist is rarely called directly in application code. It is called by the default object handler to get the CLSID of an embedded object, or an object to be marshaled. A container application, for example, would probably not call the GetClassID method directly unless it provided object handlers for specific classes of objects.

Methods in Vtable Order

IUnknown Methods | Description
QueryInterface | Returns pointers to supported interfaces.
AddRef | Increments the reference count.
Release | Decrements the reference count.

IPersist Method | Description
GetClassID | Returns the class identifier (CLSID) for the component object.