How to Alter the DLL Search Path for Statically Linked DLLs When the DLL is Not in the Application Directory?

Altering DLL Search Path for Statically Linked DLLs

Dilemma:

When statically linking a DLL to an application, it typically searches for the DLL within the application's directory. However, in certain scenarios, the DLL might not be located within the same directory. For instance, it could reside in a subfolder designated for "plugins."

Possible Solutions:

1. Dynamic Linking:

Consider using LoadLibrary() and GetProcAddress() instead of static linking to access the plugin's functionality. This grants greater flexibility in loading the DLL from its designated location.

2. Environment Variable Modification:

Appending the plugin folder path to the system's PATH environment variable ensures that the DLL can be located and loaded successfully.

3. Delay Load Mechanism:

Employ the delay load mechanism to defer loading the plugin functionality. Implement a custom helper function that loads the DLLs utilizing a provided path.

4. Assembly Creation:

Transform the plugin folder into an assembly by generating a .manifest file within it. Designate the "plugins" folder as a dependent assembly within the application. This directs the DLL search within the plugin folder.

5. Stub Application and Dynamic Loading:

Subdivide the application into a stub executable and a dynamically loaded component. Within the stub executable, use SetDllDirectory to indicate the plugin folder. Subsequently, invoke LoadLibrary passing the complete path to the "appstub.dll" file.

Additional Tips:

Turning a Folder into an Assembly:

To transform a directory containing DLLs into an assembly, add a file named "[folder_name].manifest" to the folder with the following content:

<assembly manifestVersion="1.0">
  <assemblyIdentity type="Win32" name="Plugins" version="1.0.0.0" processorArchitecture="x86" />
  <file name="Plugin.dll"/>
</assembly>

Pragma Directive for DLL Loading:

In Visual Studio 7 or later, use the following pragma directive to instruct your application to retrieve DLLs from the assembly rather than the local directory:

#pragma comment(linker, "/manifestdependency:\"name='Plugins' \
                         processorArchitecture='*' version='1.0.0.0' \
                         type='win32'\"")

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