Type Libraries and the Object Description Language

When you expose ActiveX objects, it allows interoperability with the programs of other vendors. For vendors to use these objects, they must have access to the characteristics of the objects (properties and methods). To make this information available developers must:

• Publish object and type definitions (for example, as printed documentation).
• Code objects into a compiled .c or .cpp file so they can be accessed using IDispatch::GetTypeInfo or implementations of the ITypeInfo and ITypeLib interfaces.
• Use the Microsoft Interface Definition Language (MIDL) compiler or the MkTypLib utility to create a type library that contains the objects, and then make the type library available.

The MIDL compiler and the MkTypLib utility both compile scripts that are written in the Object Description Language (ODL). Microsoft has expanded the Interface Definition Language (IDL) to contain the complete ODL syntax. You should use the MIDL compiler in preference to MkTypLib, since MkTypLib is being phased out and will no longer be supported.

For more information about the MIDL compiler, refer to the MIDL Programmer's Guide and Reference in the Win32 Software Development Kit (SDK).

The following descriptions and references are contained in this chapter:

• Contents of a type library
• Using MIDL and MkTypLib
• MkTypLib type library creation
• Differences between MIDL and MkTypLib
• ODL file syntax
• ODL reference