初学windows钩子遇到了问题，前来请教

问题概述：想监视按键，但按下键盘后调用不到DLL里的回调函数。

下面是钩子用到的DLL的源码：

#include <objbase.h>
#include <iostream>
using namespace std;

extern "C" __declspec(dllexport) LRESULT CALLBACK KeyboardProc(int nCode, WPARAM wParam, LPARAM lParam)
{
    cout << "KeyboardProc() is involked!" << endl;

    return CallNextHookEx(0, nCode, wParam, lParam);
}

BOOL APIENTRY DllMain(HANDLE hModel, DWORD dwReason, void* lpReserved)
{
    switch (dwReason)
    {
        case DLL_PROCESS_ATTACH:
            cout << "dll is attached!" << endl;
            break;
        case DLL_PROCESS_DETACH:
            cout << "dll is detached!" << endl;
            break;
        default:
            break;
    }

    return true;
}

下面是主程序的源码：

#include <windows.h>
#include <iostream>
using namespace std;

void main()
{
    HINSTANCE hInst = LoadLibrary("testdll.dll");

    if (NULL == hInst)
    {
        return;
    }

    HOOKPROC hkprcSysMsg = (HOOKPROC)GetProcAddress(hInst, "_KeyboardProc@12");
    cout << "hkprcSysMsg = " << hkprcSysMsg << endl;

    static HHOOK hhookSysMsg = SetWindowsHookEx(WH_KEYBOARD, hkprcSysMsg, hInst, 0);
    cout << "hhookSysMsg = " << hhookSysMsg << endl;

    Sleep(5000);

    UnhookWindowsHookEx(hhookSysMsg);
}

注：DLL中KeyboardProc的函数名是_KeyboardProc@12，我用dumpbin看过了。运行时hkprcSysMsg和hhookSysMsg都不是0。

现在的问题是运行起来后我按键调不到函数KeyboardProc(即打印不出"KeyboardProc() is involked!"这句话)。

请指点，谢谢。