ITypeInfo : IUnknown

This interface is typically used for reading information about objects.

At a Glance

This section describes ITypeInfo, an interface typically used for reading information about objects. For example, an object browser tool can use ITypeInfo to extract information about the characteristics and capabilities of objects from type libraries.

Type information interfaces are intended to describe the parts of the application that can be called by outside clients, rather than those that might be used internally to build an application.

The ITypeInfo interface provides access to the following:

• The set of function descriptions associated with the type. For interfaces, this contains the set of member functions in the interface.
  
  
• The set of data member descriptions associated with the type. For structures, this contains the set of members of the type.
  
  
• The general attributes of the type, such as whether it describes a structure, an interface, and so on.

The type description of an IDispatch interface can be used to implement the interface.

An instance of ITypeInfo provides various information about the type of an object, and is used in different ways. A compiler can use an ITypeInfo to compile references to members of the type. A type interface browser can use it to find information about each member of the type. An IDispatch implementor can use it to provide automatic delegation of IDispatch calls to an interface.

Type Descriptions

The information associated with an object described by ITypeInfo can include a set of functions, a set of data members, and various type attributes. It is essentially the same as the information described by a C++ class declaration, which can be used to define both interfaces and structures, as well as any combination of functions and data members. In addition to interfaces and structure definitions, the ITypeInfo interface is used to describe other types, including enumerations and aliases. Because the interface to a C file or library is simply a set of functions and variable declarations, ITypeInfo can also be used to describe them.

Type information comprises individual type descriptions. Each type description must have one of the following forms:

Note

All bit flags that are not used specifically should be set to zero for future compatibility.

Alias

An alias has TypeKind = TKIND_ALIAS. An alias is an empty set of functions, an empty set of data members, and a type description (located in the TYPEATTR), which gives the actual type definition (typedef) of the alias.

Enumeration (Statement)

An enumeration (enum) has TypeKind = TKIND_ENUM. An enumeration is an empty set of functions and a set of constant data members.

Structure (Statement)

A structure (struct) description has TypeKind = TKIND_RECORD. A structure is an empty set of functions and a set of per-instance data members.

Union (Statement)

A union description has TypeKind = TKIND_UNION. A union is an empty set of functions and a set of per-instance data members, each of which has an instance offset of zero.

Module (Statement)

A module has TypeKind = TKIND_MODULE. A module is a set of static functions and a set of static data members.

OLE-Compatible Interface

An interface definition has TypeKind = TKIND_INTERFACE. An interface is a set of pure virtual functions and an empty set of data members. If a type description contains any virtual functions, then the pointer to the VTBL is the first 4 bytes of the instance.

The type information fully describes the member functions in the VTBL, including parameter names and types and function return types. It may inherit from no more than one other interface.

With interfaces and dispinterfaces, all members should have different names, except the accessor functions of properties. For property functions having the same name, the documentation string and Help context should be set for only one of the functions (because they define the same property conceptually).

IDispatch Interface

These include objects (TypeKind = TKIND_DISPATCH) that support the IDispatch interface with a specification of the dispatch data members (such as properties) and methods supported through the object’s Invoke implementation. All members of the dispinterface should have different IDs, except for the accessor functions of properties.

Dual Interface

Dual interfaces have two different type descriptions for the same interface. The TKIND_INTERFACE type description describes the interface as a standard OLE Component Object Model (COM) interface. The TKIND_DISPATCH type description describes the interface as a standard dispatch interface. The lcid and retval parameters, and the HRESULT return types are removed, and the return type of the member is specified to be the same type as the retval parameter.

By default, the TYPEKIND enumeration for a dual interface is TKIND_INTERFACE. Tools that bind to interfaces should check the type flags for TYPEFLAG_FDUAL. If this flag is set, the TKIND_DISPATCH type description is available through a call to ITypeInfo::GetRefTypeOfImplType with an index of –1, followed by a call to ITypeInfo::GetRefTypeInfo.

Component Object Classes

These coclass objects (TypeKind = TKIND_COCLASS) support a set of implemented interfaces, which can be of either TKIND_INTERFACE or TKIND_DISPATCH.