Definition and Explanation of a .DLL file

• Microsoft Windows operating system versions 3.0, 3.1

SUMMARY

A DLL (dynamic link library) file is an executable file that allows applications to share code and other resources necessary to perform particular tasks. Microsoft Windows provides DLL files that contain functions and resources that allow Windows-based applications to operate in the Windows environment.

MORE INFORMATION

DLLs most often appear as files with a .DLL extension; however, they may also have an .EXE or other extension. For example, SHELL.DLL provides the OLE drag and drop routines the Windows and other programs use.

KERNEL.EXE, USER.EXE, and GDI.EXE are examples of DLLs with .EXE extensions. They provide code, data, or routines to applications running in the Windows operating system. For example, one of these files provides the "CreateWindow" function, which applications use when they want to create a new window on the screen.

In Windows, an installable driver is also a DLL. An application can open, enable, query, disable, and close the driver.

DLLs may be found in the WINDOWS directory, WINDOWS\SYSTEM directory, or in an application's directory.

If an application is started and one of its DLL files is missing, the error message "CANNOT FIND xxx.DLL FILE" will appear. If an application is started with an outdated DLL file, the error message "CALL TO UNDEFINED DYNALINK" will appear. In both situations, the proper DLL file must be obtained and placed in the proper directory for the application to run correctly.

REFERENCES

"Microsoft C for Windows," Microsoft Corporation, 1991 "Microsoft Windows Resource Kit," Microsoft Corporation, 1992, pages 449, 452 "Microsoft Software Developers Kit: Programmer's Reference, Volume 1: Overview," Microsoft Corporation, 1992, page 441