Linking with an Import Library

The figure below illustrates a simple case in which you create an application that uses a single dynamic-link library (.DLL) file.

┌──────────┐   ┌─────────┐       ┌─────────┐   ┌──────────┐
│ .OBJ and │   │.DEF file│       │.LIB file│   │ .OBJ and │
│.LIB files│   │(LIBRARY)│       │(imports)│   │.LIB files│
│          │   │(exports)│       │         │   │          │
└────┬─────┘   └──┬───┬──┘       └──┬───┬──┘   └────┬─────┘
     │            │   │             │   │           │
     └──────┬─────┘   │                └─────┬─────┘
            │         └─(2) IMPLIB─┘         │
                                             
      (1) LINK386                       (3) LINK386
                                             
            │                                 │
       ┌────┴────┐                     ┌──────┴──────┐
       │.DLL file│                     │ .EXE file   │
       │(library)│                     │(application)│
       └─────────┘                     └─────────────┘

As depicted above, linking occurs in three steps:

• Object files (and dynamic-link libraries) are linked with a module definition (.DEF) file to create a .DLL file. A .DEF file is used that defines all functions exported by the .DLL file.

• The IMPLIB program is used to generate an import library (.LIB) file. IMPLIB takes as input the same module definition file used in the first step. For each export definition in the .DEF file, IMPLIB generates a corresponding import definition. (IMPLIB can also use the .DLL file generated in step 1 if you use the _export keyword in C declarations to export functions.)

• The .LIB file generated by IMPLIB is used as input to LINK386, which creates an application (.EXE) file. This .LIB file provides LINK386 with information about imported dynamic-link functions.