Exports and imports
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 To make a function available to other .EXEs or .DLL files, known
 collectively as modules, the DLL exports the function in the EXPORTS section
 of the module definition file. A function can be exported in one of two
 ways, by name or by function number, known as an ordinal number. These
 alternatives are discussed in more detail in the section entitled 'Coding
 for DLLs' below.

 For a module to use a function contained in another module, it imports the
 function to create a dynamic link to the code for that function, either by
 name or by ordinal number. There are two ways to import a function into a
 module:

 . By linking the module with an import library which contains
   information for that function.

 . By listing the individual function in the IMPORTS section of the
   module definition file.

 For example, when linking applications for Windows with the normal language
 run time libraries, it is also necessary to link with the library LIBW.LIB
 (MS Visual C++) or IMPORTS.LIB (Borland C++), which contain definitions of
 all the Windows API functions. These are a special kind of library, called
 an import library, which allow the linker to resolve references (calls) to
 functions which reside in DLLs. In this case, these are references to
 Windows application programming interface (API) functions in the system
 DLLs, such as USER, KERNEL and GDI.

 When a program refers to a function defined in an import library, the linker
 includes the name of the library and a reference to the individual function
 in the header of the EXE file. When the application is loaded, these
 references are then resolved to the appropriate functions in the appropriate
 DLLs.

 Only functions which are explicitly called from another module need to be
 exported from the DLL and imported to the module. There is no need to export
 functions which are only used internally to the DLL itself.

 Import libraries are created by an import librarian such as BLILIB.EXE which
 is supplied with Blinker, or IMPLIB.EXE which is supplied with Microsoft
 Visual C++. For details on using BLILIB, please see the section entitled
 'The BLILIB import librarian' later in this chapter.