The Primary Type Library Header File

The primary type library header file consists of seven sections:

1. Heading boilerplate:   Consists of comments, #include statement for COMDEF.H (which defines some standard macros used in the header), and other miscellaneous setup information.
   
    
2. Forward references and typedefs:   Consists of structure declarations such as struct IMyInterface, and typedefs for any TKIND_ALIAS items.
   
    
3. Smart pointer declarations:    The template class _com_ptr_t is a smart-pointer implementation that encapsulates interface pointers and eliminates the need to call AddRef, Release, QueryInterface functions. In addition, it hides the CoCreateInstance call in creating a new COM object. This section uses macro statement _COM_SMARTPTR_TYPEDEF to establish typedefs of COM interfaces to be template specializations of the _com_ptr_t template class. For example, for interface IFoo, the .TLH file will contain:
   
   _COM_SMARTPTR_TYPEDEF(IFoo, __uuidof(IFoo));

which the compiler will expand to:

typedef _com_ptr_t<_com_IIID<IFoo, __uuidof(IFoo)> > IFooPtr;

Type IFooPtr can then be used in place of the raw interface pointer IFoo*. Consequently, there is no need to call the various IUnknown member functions.
   
    
4. Typeinfo declarations:   Primarily consists of class definitions and other items exposing the individual typeinfo items returned by ITypeLib:GetTypeInfo. In this section, each typeinfo from the type library is reflected in the header in a form dependent on the TYPEKIND information.
   
    
5. Optional old-style GUID definition:   Contains initializations of the named GUID constants. These are names of the form CLSID_CoClass and IID_Interface, similar to those generated by the MIDL compiler.
   
    
6. #include statement for the secondary type library header.
   
    
7. Footer boilerplate:   Currently includes #pragma pack(pop).

All sections, except the heading boilerplate and footer boilerplate section, are enclosed in a namespace with its name specified by the library statement in the original IDL file. You can use the names from the type library header either by an explicit qualification with the namespace name or by including the following statement:

using namespace MyLib;

immediately after the #import statement in the source code.

The namespace can be suppressed by using the no_namespace attribute of the #import directive. However, suppressing the namespace may lead to name collisions. The namespace can also be renamed by the rename_namespace attribute.

The compiler provides the full path to any type library dependency required by the type library it is currently processing. The path is written, in the form of comments, into the type library header (.TLH) that the compiler generates for each processed type library.

If a type library includes references to types defined in other type libraries, then the .TLH file will include comments of the following sort:

//
// Cross-referenced type libraries:
//
//  #import "c:\path\typelib0.tlb"
//

The actual filename in the #import comment is the full path of the cross-referenced type library, as stored in the registry. If you encounter errors that are due to missing type definitions, check the comments at the head of the .TLH to see which dependent type libraries may need to be imported first. Likely errors are syntax errors (e.g. C2143, C2146, C2321), C2501 (missing decl-specifiers), or C2433 ('inline' not permitted on data declaration) while compiling the .TLI file.

You must determine which of the dependency comments are not otherwise provided for by system headers and then provide an #import directive at some point before the #import directive of the dependent type library in order to resolve the errors.