Classes in Windows programming?

From:
=?Utf-8?B?Um9iYnk=?= <Robby@discussions.microsoft.com>
Newsgroups:
microsoft.public.vc.language
Date:
Mon, 24 Apr 2006 18:04:01 -0700
Message-ID:
<7F323658-6F4F-4F7B-A07C-7B035F697BAE@microsoft.com>
Hello,

Please consider the following code:

=====================================================
class Cat
{
public:
Cat(int initialAge); //Constructor
~Cat(); //Destructor
int getAge();
void setAge(int age);
void Meow(HDC hdc,RECT rect);
private:
int itsAge;
};

//Constructor
Cat::Cat(int initialAge)
{
itsAge = initialAge;
}

//Destructor
Cat::~Cat()
{}

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM
lParam)
{
HDC hdc;
PAINTSTRUCT ps;
TEXTMETRIC tm;
RECT rect;

case WM_CREATE:

//Instantiate classes
Cat Frisky(11); //Constructor

....Other code

return 0;

//I want my paint handler to fetch these Cat methods
case WM_PAINT:
Frisky.setAge(5);
Frisky.Meow(hdc,rect);

....other code

return 0
===================================================

Based on the code above, I get the following error:
 
C:\_DTS_PROGRAMMING\_EVC_Examples\eVC_for_PLC\EVC_PLC\WndProc.cpp(168) :
error C2360: initialization of 'Frisky' is skipped by 'case' label

This error basically says:

"The initialization of identifier can be skipped in a switch statement. You
cannot jump past a declaration with an initializer unless the declaration is
enclosed in a block. (Unless it is declared within a block, the variable is
within scope until the end of the switch statement.)"

So if I tried to move the "Cat Frisky(11);" like so:

=================================================
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM
lParam)
{

HDC hdc;
PAINTSTRUCT ps;
TEXTMETRIC tm;
RECT rect;
Cat Frisky(11);
================================================

But this gave me the following two errors:

C:\_DTS_PROGRAMMING\_EVC_Examples\eVC_for_PLC\EVC_PLC\WndProc.cpp(181) :
warning C4700: local variable 'rect' used without having been initialized

C:\_DTS_PROGRAMMING\_EVC_Examples\eVC_for_PLC\EVC_PLC\WndProc.cpp(181) :
warning C4700: local variable 'hdc' used without having been initialized

And if I declare RECT and HDC as static, the app would compile however then
Frisky.Meow() would not display appropriately... further... it would not
display at all, here is the method:

void Cat::Meow(HDC hdc,RECT rect)
{
TCHAR szBuffer[2];

wsprintf(szBuffer,TEXT("%d"),itsAge);
DrawText (hdc,szBuffer,-1, &rect,
      DT_CENTER | DT_BOTTOM | DT_SINGLELINE);

DrawText (hdc,TEXT ("Message in Method"),-1, &rect,
      DT_CENTER | DT_TOP | DT_SINGLELINE);
}

This is my first attempt of combining C++ with Win32 API's (Windows
programming)

I am just trying to underdtand the basic rule of thumb of, where I am
supposed to innitiate my class objects and so that I can use its methods in
my windows handlers?

All suggestions appreciated.....

Thanking you guys in advance!

--
Kind regards
Robert

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