why is this function failing?

Question

am trying to understand windows hooks by writing a few keyboard hooks. i have a function,

bool WriteToFile(WPARAM keyCode, char * fileName)
{
    ofstream fout("filename");
    if(fout.is_open())
    {
        if(keyCode>=0x030 && keyCode<0x039)
            fout<< (keyCode - 0x030);
            fout.close();
        return true;
    }
    else        fout.close();
        return false;
}

That i try to call from here but it almost always fails. Why??

LRESULT CALLBACK KbHookProc(int nCode, WPARAM wParam, LPARAM lParam)
{
if(nCode > 0)
             {
                 WriteToFile(wParam,"log.txt");  //this function always fails . Why 
             }
else return CallNextHookEx(hCurrentHook, nCode, wParam, lParam);
}