c - GetProcAddress 返回 NULL

Question

我必须使用 DLL 中的一个简单函数；我能够加载库，但 GetProcAddress 返回 NULL。我想我了解名称修改，但也许我做错了什么。谢谢(代码如下，我会尽快添加所需的其他信息):

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);
}

来自 main.cpp 的代码

...
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;
...

Answer 1

是的，MessageBox() 调用成功且没有错误。将 GetLastError() 调用移到它之前。

错误是可以预测的，它找不到“mouseProc”。该名称将在 DLL 中被破坏，很可能是“_mouseProc@12”。确保在您的 DLL 上使用 dumpbin.exe/exports。

Fwiw:您可以通过不动态加载 DLL 而只是链接其导入库来减轻这段代码的痛苦。 DLL 将被注入(inject)到其他进程的事实并不意味着您必须将它注入(inject)到您的进程中。您只需要模块句柄，这样您就可以调用 SetWindowsHookEx()。从 DllMain() 入口点或使用 GetModuleHandle() 获取它。