module-definition-dot-def-files.md

description	Learn more about: Module-Definition (.Def) Files
title	Module-Definition (.Def) Files
ms.date	11/04/2016
helpviewer_keywords	def files module definition files .def files
ms.assetid	08c0bc28-c5d2-47aa-9624-7fc68bcaa4d8

Module-Definition (.Def) Files

Module-definition (.def) files provide the linker with information about exports, attributes, and other information about the program to be linked. A .def file is most useful when building a DLL. Because there are MSVC Linker Options that can be used instead of module-definition statements, .def files are generally not necessary. You can also use __declspec(dllexport) as a way to specify exported functions.

You can invoke a .def file during the linker phase with the /DEF (Specify Module-Definition File) linker option.

If you are building an .exe file that has no exports, using a .def file will make your output file larger and slower loading.

For an example, see Exporting from a DLL Using DEF Files.

See the following sections for more information:

• Rules for Module-Definition Statements

• EXPORTS

• HEAPSIZE

• LIBRARY

• NAME

• SECTIONS

• STACKSIZE

• STUB

• VERSION

• Reserved words

See also

C/C++ Building Reference
MSVC Linker Options