Importing Files and Type Libraries

The MIDL keywords include, import, and importlib let you reuse code by referencing existing header, IDL, and object definition language (ODL) files, and compiled type libraries.

The ACF include directive lets you specify in an ACF file one or more C-language header files to be included in the MIDL-generated stub code. The generated file will have a line with a #include C-preprocessor directive with the indicated header file. Use this include directive to bring in header files that are specific to a particular operating environment and that do not contain information necessary for the interface between client and server. Do not use include for header files containing data types that you want available to the IDL file; instead, use the import directive.

Example 1

interface X86PC
  include "gendefs.h", "protos.h", "myfile.h"; 
  //interface typdefs and function declarations here

The IDL import directive is the standard method for bringing type and interface definitions from other IDL (or ODL) files and header files into your IDL file. All IDL statements in the imported file, such as typedefs, const declarations, and interface definitions become available to the importing IDL file.

Like the C-language preprocessor directive #include, the import directive tells the compiler to include data types that were defined in the imported IDL files. Unlike the #include directive, the import directive ignores procedure prototypes, since no stubs are generated for anything in the imported file. Because the preprocessor is invoked separately for the imported file, preprocessor directives (such as **) do not carry over to the importing IDL file.

For additional information on using import to include system header files in an IDL file, see Importing System Header Files.

Example 2

  uuid(. . .), object
interface IKnown : IUnknown
  import "base.idl", "unknwn.idl", "helper.idl";
  //remainder of interface definition

The ODL importlib directive lets you reference a compiled type library in your IDL or ODL file. The importlib directive must be inside a library statement, and must precede other type descriptions in the library. The imported library, as well as the generated library, must be available to the application at runtime.

Example 3

library NewBrowser
  //remainder of library definition

You can also use the C-preprocessor #include directive to include headers and other files in your IDL or ODL file. Be aware, however, that this directive will literally include the entire contents of the specified file. If a header file contains prototypes that you do not need or want in the MIDL-generated stub files, or if it contains nonremotable type definitions, you should use the MIDL import directive instead of the #include directive.




Importing System Header Files