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How to use Rundll32 to execute DLL Function?

Where can I find documentation (tutorials, books, etc.) to write my own dll’s that can be run with rundll32.exe?

Answer 1

Here is the most basic Hello World sample I could come up with that will work with rundll.exe. Please follow along these steps:

Start a fresh WIN32 DLL project in Visual Studio (I used VS2010)

In dlllmain.cpp add:

// this shoud ideally go into the .h file I believe
__declspec( dllexport ) void CALLBACK EntryPoint(
       HWND hwnd, 
      HINSTANCE hinst, 
      LPSTR lpszCmdLine, 
      int nCmdShow);

// our hello world function
void CALLBACK EntryPoint(HWND hwnd, HINSTANCE hinst, LPSTR lpszCmdLine, int nCmdShow)
{
    int msgboxID = MessageBox(
        NULL,
        L"Hello World from Run32dll",
        L"Hello World",
        MB_ICONWARNING | MB_CANCELTRYCONTINUE | MB_DEFBUTTON2
    );

    switch (msgboxID)
    {
    case IDCANCEL:
        // TODO: add code
        break;
    case IDTRYAGAIN:
        // TODO: add code
        break;
    case IDCONTINUE:
        // TODO: add code
        break;
    }

}

Add a module.def file to your project and edit the following snippet in it:

LIBRARY YourDll
EXPORTS
    EntryPoint

Compile and then test from the commandline with

rundll32 YourDll.dll,EntryPoint

You should be greeted with a MessageBox with three buttons

I used the following url’s to overcome C++ issues and EntryPoint not found in the early stages of my effort:

• Rundll from user mricicle
• How messagebox works
• DependencyWalker
• Exporting functions
• Exporting with .def file
• String literals