C++ Unknown override specifier when using function in callback - c++

Question

I'm working with C++ and the Windows API now for just a little while. I've never used a callback in C++ since yesterday, when the Windows API required me to do so for installing a low level mouse event hook (link to hook function). To keep my code a little cleaner I wanted to outsource some code to a function and then I ran into a problem that I don't understand. I think it has to do something with me not totally understanding the callback scope or something like that. My code looks like this and I use C++11 and VS2017:
MouseHandler.h
#ifndef __MOUSEHANDLER_H_INCLUDED__
#define __MOUSEHANDLER_H_INCLUDED__
#include <Windows.h>
class MouseHandler
{
private:
public:
static _bstr_t coordinatesToString(POINT point);
MouseHandler();
~MouseHandler();
};
#endif // !__MOUSEHANDLER_H_INCLUDED__
MouseHandler.cpp
#include "stdafx.h"
#include "MouseHandler.h"
#include <comutil.h>
#include <string>
using namespace std;
HHOOK mouseHook = NULL;
_bstr_t MouseHandler::coordinatesToString(POINT point)
{
_bstr_t coordinates = "(";
_bstr_t xcoordinate = to_string(point.x).c_str();
_bstr_t ycoordinate = to_string(point.y).c_str();
coordinates += xcoordinate + "," + ycoordinate + ")";
return coordinates;
}
LRESULT CALLBACK MouseHookCallback(int nCode, WPARAM wParam, LPARAM lParam)
{
MSLLHOOKSTRUCT event = *((MSLLHOOKSTRUCT *)lParam);
if (nCode == HC_ACTION)
{
_bstr_t message = "Mouse action happened at position: ";
_bstr_t mouseCoordinates = MouseHandler::coordinatesToString(event.pt);
message += mouseCoordinates;
}
return CallNextHookEx(mouseHook, nCode, wParam, lParam);
}
MouseHandler::MouseHandler()
{
mouseHook = SetWindowsHookEx(WH_MOUSE_LL, MouseHookCallback, NULL, 0);
while (GetMessage(NULL, NULL, 0, 0) != 0);
}
MouseHandler::~MouseHandler()
{
}
When I try to compile I get the error C3646 'coordinatesToString': unknown override specifier. I searched up and down and asked my colleagues, but I couldn't get help with this, so I hope someone here can help me. Thanks in advance!

Answer 1

Make sure you specify the correct type of data.
to_string((long double)point.x).c_str();
Load the lib.
#pragma comment (lib, "comsuppw.lib")
or
#pragma comment (lib, "comsuppwd.lib")
Include comutil.h to the header CMouseHandler.h.
I tested your code in VS2010 C++ on Win10 1803 x64.
CMouseHandler.h
#pragma once
#include <Windows.h>
#include <comutil.h>
#include <string>
using namespace std;
#pragma comment (lib, "comsuppw.lib")
class CMouseHandler
{
public:
CMouseHandler(void);
~CMouseHandler(void);
static _bstr_t coordinatesToString(POINT point);
};
CMouseHandler.cpp
#include "CMouseHandler.h"
HHOOK mouseHook = NULL;
_bstr_t CMouseHandler::coordinatesToString(POINT point)
{
_bstr_t coordinates = "(";
_bstr_t xcoordinate = to_string((long double)point.x).c_str();
_bstr_t ycoordinate = to_string((long double)point.y).c_str();
coordinates += xcoordinate + "," + ycoordinate + ")";
return coordinates;
}
LRESULT CALLBACK MouseHookCallback(int nCode, WPARAM wParam, LPARAM lParam)
{
MSLLHOOKSTRUCT event = *((MSLLHOOKSTRUCT *)lParam);
if (nCode == HC_ACTION)
{
_bstr_t message = "Mouse action happened at position: ";
_bstr_t mouseCoordinates = CMouseHandler::coordinatesToString(event.pt);
message += mouseCoordinates;
}
return CallNextHookEx(mouseHook, nCode, wParam, lParam);
}
CMouseHandler::CMouseHandler()
{
mouseHook = SetWindowsHookEx(WH_MOUSE_LL, MouseHookCallback, NULL, 0);
while (GetMessage(NULL, NULL, 0, 0) != 0);
}
CMouseHandler::~CMouseHandler(void)
{
}

Answer 2

_bstr_t isn't defined, as visual studio doesn't recognise the type it assumes its an override specifier. You need to include comutil.h as specified in the documentation.