Static function pointer linker error

Hello all,

I'm writing a class with a static function pointer in it, however I'm getting a linker error saying that it is an unresolved external symbol. Here's my code:

BindHook.h

Code:

---

#ifndef BINDHOOK
#define BINDHOOK

#include <Windows.h>

class BindHook
{
public:
        static HHOOK kbHook, msHook;

        static bool (*onKeyEvent)(int vkey, WPARAM msg);
       
        static void InitHooks();
        static void StopHooks();

        static LRESULT CALLBACK KeyboardProc(int nCode, WPARAM wParam, LPARAM lParam);
        static LRESULT CALLBACK MouseProc(int nCode, WPARAM wParam, LPARAM lParam);
};

#endif

---

BindHook.cpp

Code:

---

#include "BindHook.h"

bool (BindHook::*onKeyEvent)(int vkey, WPARAM msg) = NULL;

HHOOK BindHook::kbHook = 0;
HHOOK BindHook::msHook = 0;

LRESULT CALLBACK BindHook::KeyboardProc(int nCode, WPARAM wParam, LPARAM lParam)
{
        if (nCode != HC_ACTION)
                return CallNextHookEx(kbHook, nCode, wParam, lParam);
       
        //get the struct
        PKBDLLHOOKSTRUCT kb = (PKBDLLHOOKSTRUCT)lParam;

        //injected key?
        bool inj = ((kb->flags & 0x00000010) == 16);

        //call fn's
        if ((wParam == WM_KEYDOWN || wParam == WM_KEYUP) && !inj)
                if (onKeyEvent(kb->vkCode, wParam))
                        return true;

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

LRESULT CALLBACK BindHook::MouseProc(int nCode, WPARAM wParam, LPARAM lParam)
{
        if (nCode != HC_ACTION)
                return CallNextHookEx(msHook, nCode, wParam, lParam);

        PMSLLHOOKSTRUCT ms = (PMSLLHOOKSTRUCT)lParam;
        bool inj = ((ms->flags & 0x00000001) == 1);
        int vk = -1;

        //determine VKEY
        switch (wParam)
        {
        case WM_LBUTTONUP: case WM_LBUTTONDOWN:
                vk = VK_LBUTTON;
                break;
        case WM_RBUTTONUP: case WM_RBUTTONDOWN:
                vk = VK_LBUTTON;
                break;
        case WM_MBUTTONUP: case WM_MBUTTONDOWN:
                vk = VK_LBUTTON;
                break;
        case WM_XBUTTONUP: case WM_XBUTTONDOWN:
                vk = ((ms->mouseData >> 16 ) & 0xFFFF) == 1 ? VK_XBUTTON1 : VK_XBUTTON2;
                break;
        }

        switch (wParam)
        {
        case WM_LBUTTONUP:
        case WM_RBUTTONUP:
        case WM_MBUTTONUP:
        case WM_XBUTTONUP:
                if (!inj)
                        if(onKeyEvent(vk, WM_KEYUP))
                                return true;
                break;
        case WM_LBUTTONDOWN:
        case WM_RBUTTONDOWN:
        case WM_MBUTTONDOWN:
        case WM_XBUTTONDOWN:
                if (!inj)
                        if(onKeyEvent(vk, WM_KEYDOWN))
                                return true;
                break;
        }

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

void BindHook::InitHooks()
{
        kbHook = SetWindowsHookEx(WH_KEYBOARD_LL, (HOOKPROC)KeyboardProc, NULL, NULL);
}

void BindHook::StopHooks()
{
        UnhookWindowsHookEx(kbHook);
}

---

The specific Error:

Code:

---

Error        1        error LNK2001: unresolved external symbol "public: static bool (__cdecl* BindHook::onKeyEvent)(int,unsigned int)" (?onKeyEvent@BindHook@@2P6A_NHI@ZA)        C:\[...]\BindHook.obj        BindSystem_Console

---

Any help would be greatly appreciated.

Thanks,

-Matt

Code:

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bool (BindHook::*onKeyEvent)(int vkey, WPARAM msg) = NULL;

---

This should be

Code:

---

bool (*(BindHook::onKeyEvent))(int vkey, WPARAM msg) = NULL;

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I don't know how to explain this particular function pointer rule. I think that perhaps BindHook::*onKeyEvent is the type, and *(BindHook:: onKeyEvent) is the variable itself (that's just speculation though).

The situation becomes much clearer if you use typedefs (I'd recommend the typedefs route any time you need function pointers):

Code:

---

//in the header
class BindHook
{
    ...
    typedef bool (*KeyEventFunc)(int vkey, WPARAM msg);
    static KeyEventFunc onKeyEvent;
    ...
};

//and in the code
BindHook::KeyEventFunc BindHook::onKeyEvent = NULL;

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Even better:

Code:

---

typedef bool (KeyEventFunc_t)(int vkey, WPARAM msg);
KeyEventFunc_t* KeyEventFunc;

---

As with any static variable, you need to define them in a source file (and only once):

Code:

---

KeyEventFunc_t* MyClass::KeyEventFunc;

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