How to Specify a DllImport Path Dynamically in C#?

How to specify DllImport path at runtime?

In C#, the DllImport attribute is used to import functions from an unmanaged DLL into managed C# code. The path parameter of this attribute usually specifies the full path to the DLL. However, when faced with the challenge of cross-platform installation, where users' folder paths vary, specifying a fixed path becomes impractical.

Proposed solution (and its limitations)

To solve this problem, an alternative is to utilize the Path.GetTempPath() method to dynamically determine the temporary folder path of the current user profile. From there, you can navigate to the user's local application data folder and then proceed to the desired DLL subfolder.

However, the DllImport trait expects a const string parameter, which creates obstacles in runtime path construction.

Correct method: Use Win32 DLL loading rules

The recommended method is to continue using the DllImport feature. The solution lies in understanding the native Win32 DLL loading rules, which control the search order for specified DLLs:

1. DLL with the same name loaded in memory
2. Known DLLs for current Windows versions
3. If enabled, the search path includes:
   • Application loading directory
   • System Directory
   • 16-bit system directory
   • Windows Directory
   • Current Directory
   • Directories listed in the PATH environment variable

By using the relative path of the DllImport attribute, the system will prioritize its application load directory to search for the DLL. This ensures successful execution even in different installation folder paths.

Dynamic solution: use SetDllDirectory function

If you need absolute path specification, you can use the SetDllDirectory function. This function modifies the default search path and allows the use of dynamic values ​​based on runtime calculations. Call this function before calling any imported DLL functions and the changed search path will take effect.

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