Dynamic-Link Library Redirection

Problems can occur when an application loads a version of a DLL other than the one with which it shipped. Starting with Windows 2000, you can ensure that your application uses the correct version of a DLL by creating a redirection file. The contents of a redirection file are ignored, but its presence forces all DLLs in the application's directory to be loaded from that directory.

The redirection file must be named as follows:

appname.local

For example, if the application's name is editor.exe, the redirection file is named editor.exe.local. You must install editor.exe.local in the same directory that contains editor.exe. You must also install the DLLs in the same directory.

The LoadLibrary and LoadLibraryEx functions change their search sequence if a redirection file is present. If a path is specified and there is a redirection file for the application, these functions search for the DLL in the application's directory. If the DLL exists in the application's directory, these functions ignore the specified path and load the DLL from the application's directory. If the module is not in the application's directory, these functions load the DLL from the specified directory.

For example, an application c:\myapp\myapp.exe calls LoadLibrary using the following path:

c:\program files\common files\system\mydll.dll. 

If c:\myapp\myapp.exe.local and c:\myapp\mydll.dll exist, LoadLibrary will load c:\myapp\mydll.dll. Otherwise, LoadLibrary will load c:\program files\common files\system\mydll.dll.

Note  It is good practice to install your application's DLLs in the same directory that contains the application, even if you are not using redirection. It ensures that installing your application will not overwrite other copies of the DLL and cause other applications to fail. In addition, other applications will not overwrite your copy of the DLL and cause your application to fail.