The definition file supplies information to the linker about the DLL, such as the library name and how the functions being exported.
The following example is written for use with the Microsoft Visual C++ compiler:
;DESCRIPTION 'Copyright (C) 1982-2016 ESL Syndetic Limited. All rights reserved.'
EXPORTS
HasUpper @1
MakeUpper @2
HasLower @3
MakeLower @4
MakeBackwards @5
Some compilers require DLLMain for DLLs. Refer to your compiler documentation for details.