Can Dynamic DLL Paths Be Used with C#'s DllImport?

Does DllImport in C# support runtime dynamic paths?

When using the DllImport attribute in C#, you usually need to statically specify the path to the DLL. However, when the installation path of the application depends on the user (for example: C:UsersuserName...), hardcoding the absolute path is not practical.

Traditional method

Despite this issue, it is recommended to use relative paths. Specify only the name of the DLL and the system will search for it in the application directory and other predefined locations (according to Windows DLL loading guidelines).

SetDllDirectory and P/Invoke

If relative paths don't suit your needs, consider using the SetDllDirectory function. This function allows you to modify the default DLL search path at run time, allowing you to specify a dynamic path that is calculated at that time.

To use SetDllDirectory you need to use P/Invoke as it is a Windows API function. Here is its statement:

[DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
static extern bool SetDllDirectory(string lpPathName);

Achievement

Your code should look similar to the following:

SetDllDirectory(Path.GetTempPath() + "..\myLibFolder");

[DllImport("MyAppDll.dll")]
static extern bool MyGreatFunction(int myFirstParam, int mySecondParam);

This redirects the DLL search path to the location containing the runtime fork, before the system's standard search order.

Advantages

Using the SetDllDirectory function, you can dynamically specify the runtime location of a DLL without relying on the user's machine or installation path.

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