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Asked: 2026-05-24T12:59:30+00:00

I have to use a simple function from a DLL; I am able to

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I have to use a simple function from a DLL; I am able to load the library but GetProcAddress returns NULL. I think I understood name mangling but maybe I’m doing something wrong. Thanks (Code follows, asap I’ll add other information required):

mydll.h

#ifdef MYDLL_EXPORTS
#define MYDLL_API extern "C" __declspec(dllexport)
#else
#define MYDLL_API extern "C" __declspec(dllimport)
#endif

MYDLL_API void testFunction(void);
MYDLL_API LRESULT CALLBACK mouseProc(int nCode, WPARAM wParam, LPARAM lParam);

mydll.cpp

#include "stdafx.h"
#include "mydll.h"

// This is an example of an exported function.
MYDLL_API void testFunction(void)
{
MessageBox(NULL, (LPCWSTR)L"Test", (LPCWSTR)L"Test", MB_OK);
}

MYDLL_API LRESULT CALLBACK mouseProc(int nCode, WPARAM wParam, LPARAM lParam)
{
// processes the message
if(nCode >= 0)
{
    if(wParam != NULL && wParam == MK_RBUTTON)
    {
        MessageBox(NULL, (LPCWSTR)L"Captured mouse right button", (LPCWSTR)L"Test", MB_OK);
    }
}

// calls next hook in chain
return CallNextHookEx(NULL, nCode, wParam, lParam);
}

code from main.cpp

...
case WM_CREATE:
    {   
        // creates state for window
        stateClassPointer = new stateClass();
        // saves states pointer in a space reserved for user data
        SetWindowLongPtr(hWnd, GWLP_USERDATA, (LONG_PTR) stateClassPointer);

        // now it will load DLL and set up hook procedure for mouse events

        // declares local variables
        HOOKPROC hkprcMouseProc;
        HINSTANCE hinstDLL; 
        HHOOK hhookMouseProc; 
        //FARPROC WINAPI test;
        // loads DLL
        if((hinstDLL = LoadLibrary(TEXT("C:\\Users\\Francesco\\Dropbox\\poli\\bi\\not\\pds\\sp\\wk5\\lsp5\\Debug\\mydll.dll"))) == NULL)
        {
            MessageBox(hWnd, (LPCWSTR)L"Error loading DLL", (LPCWSTR)L"Error", MB_OK | MB_ICONERROR);
            break;
        }
        // saves DLL handle in the state class
        stateClassPointer->setHInstance(hinstDLL);
        // sets up hook procedure for mouse events
        if((hkprcMouseProc = (HOOKPROC)GetProcAddress(hinstDLL, "mouseProc")) == NULL)
        {
            MessageBox(hWnd, (LPCWSTR)L"Error setting windows hook: GetProcAddress", (LPCWSTR)L"Error", MB_OK | MB_ICONERROR);
            break;
        }
        if((hhookMouseProc = SetWindowsHookEx(WH_MOUSE, hkprcMouseProc, hinstDLL, 0)) == NULL)
        {
            MessageBox(hWnd, (LPCWSTR)L"Error setting windows hook: SetWindowsHookEx", (LPCWSTR)L"Error", MB_OK | MB_ICONERROR);
            break;
        }
        // saves hook handle in the state class
        stateClassPointer->setHHook(hhookMouseProc);
        /*test = GetProcAddress(hinstDLL, "testFunction");
        test();*/
    }
    break;
...
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1 Answer

  1. Editorial Team

    Yes, the MessageBox() call succeeded without errors. Move the GetLastError() call before it.

    The error is otherwise predictable, it couldn’t find “mouseProc”. The name will be mangled in the DLL, most probably “_mouseProc@12”. Use dumpbin.exe /exports on your DLL to be sure.

    Fwiw: you can make this code less painful by not dynamically loading the DLL but just linking its import library. The fact that the DLL will be injected into other processes doesn’t also mean you have to inject it in yours. All you need is the module handle so you can call SetWindowsHookEx(). Get that from the DllMain() entry point or by using GetModuleHandle().

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