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Today’s sample demonstrates dynamically load a native DLL by P/Invoking LoadLibrary, and invoke its exported functions.

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Introduction

CSLoadLibrary in C# mimics the behavior of CppLoadLibrary to dynamically load a native DLL (LoadLibrary) get the address of a function in the export  table (GetProcAddress, Marshal.GetDelegateForFunctionPointer), and call it.

The technology is called Dynamic P/Invoke. It serves as a supplement for the P/Invoke technique and is useful especially when the target DLL is not in the search path of P/Invoke. If you use P/Invoke, CLR will search the dll in your assembly's directory first, then search the dll in directories listed in PATH environment variable. If the dll is not in any of those directories, you have to use the so called Dynamic PInvoke technique that is demonstrated in this code sample.

Implementation

1. P/Invoke the API LoadLibrary to dynamically load a native DLL.

2. P/Invoke the API GetProcAddress to get the function pointer of a specified function in the DLL's export table.

3. Call Marshal.GetDelegateForFunctionPointer to convert the function pointer to a delegate object.

4. Call the delegate.

5. Call FreeLibrary on the unmanaged dll. (Be careful of calling kernel32!FreeLibrary from managed code! This is unsafe and can crash if done wrong.)

 

More Information

�� Type-safe Managed wrappers for kernel32!GetProcAddress

�� Dynamic PInvoke

�� MSDN: Exporting from a DLL

�� MSDN: Exporting from a DLL Using DEF Files

�� MSDN: Exporting from a DLL Using __declspec(dllexport)

�� MSDN: Creating and Using a Dynamic Link Library (C++)

�� HOWTO: How To Export Data from a DLL or an Application

�� Dynamic-link library