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Application Creation

 

The Main Window Class

There are two primary things you must do in order to create even the simplest window: you must create the central point of the program, and you must tell the operating system how to respond when the user does what.

Just like a C++ program always has a main() function, a Win32 program needs a central function call WinMain. The syntax of that function is:

INT WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
                   LPSTR lpCmdLine, int nCmdShow );

Unlike the C++ main() function, the arguments of the WinMain() function are not optional. Your program will need them to communicate with the operating system.

The first argument, hInstance, is a handle to the instance of the program you are writing.

The second argument, hPrevInstance, is used if your program had any previous instance. If not, this argument can be ignored, which will always be the case.

The third argument, lpCmdLine, is a string that represents all items used on the command line to compile the application.

The last argument, nCmdShow, controls how the window you are building will be displayed.

An object that displays on your screen is called a window. Because there can be various types of windows in your programs, your first responsibility is to control them, know where they are, what they are doing, why, and when. The first control you must exercise on these different windows is to host them so that all windows of your program belong to an entity called the main window. This main window is created using an object that can be called a class (strictly, a structure).

The Win32 library provides two classes for creating the main window and you can use any one of them. They are WNDCLASS and WNDCLASSEX. The second adds only a slight feature to the first. Therefore, we will mostly use the WNDCLASSEX structure for our lessons.

The WNDCLASS and the WNDCLASSEX classes are defined as follows:
 typedef struct _WNDCLASS { 
    UINT       style; 
    WNDPROC    lpfnWndProc; 
    int        cbClsExtra; 
    int        cbWndExtra; 
    HINSTANCE  hInstance; 
    HICON      hIcon; 
    HCURSOR    hCursor; 
    HBRUSH     hbrBackground; 
    LPCTSTR    lpszMenuName; 
    LPCTSTR    lpszClassName; 
} WNDCLASS, *PW
typedef struct _WNDCLASSEX { 
    UINT       cbSize; 
    UINT       style; 
    WNDPROC    lpfnWndProc; 
    int        cbClsExtra; 
    int        cbWndExtra; 
    HINSTANCE  hInstance; 
    HICON      hIcon; 
    HCURSOR    hCursor; 
    HBRUSH     hbrBackground; 
    LPCTSTR    lpszMenuName; 
    LPCTSTR    lpszClassName; 
    HICON      hIconSm; 
} WNDCLASSEX, *PWNDCLASSEX;

To create a window, you must "fill out" this class, which means you must provide a value for each of its members so the operating system would know what your program is expected to do.

The first thing you must do in order to create an application is to declare a variable of either WNDCLASS or WNDCLASSEX type. Here is an example of a WNDCLASSEX variable:

INT WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
               LPSTR lpCmdLine, int nCmdShow)
{
    WNDCLASSEX WndClsEx;

    return 0;
}

The Size of the Window Class

After declaring a WNDCLASSEX variable, you must specify its size. This is done by  initializing your variable with the sizeof operator applied to the window class as follows:

INT WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
               LPSTR lpCmdLine, int nCmdShow)
{
	WNDCLASSEX WndClsEx;

	WndClsEx.cbSize = sizeof(WNDCLASSEX);

    return 0;
}

Additional Memory Request

Upon declaring a WNDCLASSEX variable, the compiler allocates an amount of memory space for it, as it does for all other variables. If you think you will need more memory than allocated, assign the number of extra bytes to the cbClsExtra member variable. Otherwise, the compiler initializes this variable to 0. If you do not need extra memory for your WNDCLASSEX variable, initialize this member with 0. Otherwise, you can do it as follows:

INT WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
               LPSTR lpCmdLine, int nCmdShow)
{
	WNDCLASSEX WndClsEx;

	WndClsEx.cbSize     = sizeof(WNDCLASSEX);
	WndClsEx.cbClsExtra = 0;

	return 0;
}

The Application's Instance

Creating an application is equivalent to creating an instance for it. To communicate to the WinMain() function that you want to create an instance for your application, which is, to make it available as a resource, assign the WinMain()'s hInstance argument to your WNDCLASS variable:

INT WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
               LPSTR lpCmdLine, int nCmdShow)
{
	WNDCLASSEX WndClsEx;

	WndClsEx.cbSize     = sizeof(WNDCLASSEX);
	WndClsEx.cbClsExtra = 0;
	WndClsEx.hInstance  = hInstance;

	return 0;
}

Window Extra-Memory

When an application has been launched and is displaying on the screen, which means an instance of the application has been created, the operating system allocates an amount of memory space for that application to use. If you think that your application's instance will need more memory than that, you can request that extra memory bytes be allocated to it. Otherwise, you can let the operating system handle this instance memory issue and initialize the cbWndExtra member variable to 0:

INT WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
               LPSTR lpCmdLine, int nCmdShow)
{
	WNDCLASSEX WndClsEx;

	WndClsEx.cbSize     = sizeof(WNDCLASSEX);
	WndClsEx.cbClsExtra = 0;
	WndClsEx.cbWndExtra = 0;
	WndClsEx.hInstance  = hInstance;

	return 0;
}

The Main Window's Style

The style member variable specifies the primary operations applied on the window class. The actual available styles are constant values. For example, if a user moves a window or changes its size, you would need the window to be redrawn to get its previous characteristics. To redraw the window horizontally, you would apply the CS_HREDRAW. In the same way, to redraw the window vertically, you can apply the CS_VREDRAW.

The styles are combined using the bitwise OR (|) operator. The CS_HREDRAW and the CS_VREDRAW styles can be combined and assigned to the style member variable as follows:

INT WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
               LPSTR lpCmdLine, int nCmdShow)
{
	WNDCLASSEX WndClsEx;

	WndClsEx.cbSize     = sizeof(WNDCLASSEX);
	WndClsEx.style      = CS_HREDRAW | CS_VREDRAW;
	WndClsEx.cbClsExtra = 0;
	WndClsEx.cbWndExtra = 0;
	WndClsEx.hInstance  = hInstance;

	return 0;
}
 
 

Message Processing

The name of the window procedure we reviewed in the previous lesson must be assigned to the lpfnWndProc member variable of the WNDCLASS or WNDCLASSEX variable. This can be defined as follows:

#include <windows.h>

LRESULT WndProcedure(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam);

INT WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
               LPSTR lpCmdLine, int nCmdShow)
{
	WNDCLASSEX WndClsEx;

	WndClsEx.cbSize      = sizeof(WNDCLASSEX);
	WndClsEx.style       = CS_HREDRAW | CS_VREDRAW;
	WndClsEx.lpfnWndProc = WndProcedure;
	WndClsEx.cbClsExtra  = 0;
	WndClsEx.cbWndExtra  = 0;
	WndClsEx.hInstance   = hInstance;

	return 0;
}

LRESULT CALLBACK WndProcedure(HWND hWnd, UINT Msg, WPARAM wParam, LPARAM lParam)
{
    switch(Msg)
    {
    case WM_DESTROY:
        PostQuitMessage(WM_QUIT);
        break;
    default:
        return DefWindowProc(hWnd, Msg, wParam, lParam);
    }
    return 0;
}

The Application Main Icon

An icon can be used to represent an application in My Computer or Windows Explorer. To assign this small picture to your application, you can either use an existing icon or design your own. To make your programming a little faster, Microsoft Windows installs a few icons. The icon is assigned to the hIcon member variable using the LoadIcon() function. For a Win32 application, the syntax of this function is:

HICON LoadIcon(HINSTANCE hInstance, LPCTSTR lpIconName);

The hInstance argument is a handle to the file in which the icon was created. This file is usually stored in a library (DLL) of an executable program. If the icon was created as part of your application, you can use the hInstance of your application. If your are using one of the icons below, set this argument to NULL.

The lpIconName is the name of the icon to be loaded. This name is added to the resource file when you create the icon resource. It is added automatically if you add the icon as part of your resources; otherwise you can add it manually when creating your resource script. Normally, if you had created and designed an icon and gave it an identifier, you can pass it using the MAKEINTRESOURCE macro.

To make your programming a little faster, Microsoft Windows installs a few icons you can use for your application. These icons have identification names that you can pass to the LoadIcon() function as the lpIconName argument. The icons are:

ID Picture
IDI_APPLICATION Application Icon
IDI_INFORMATION Information
IDI_ASTERISK Asterisk
IDI_QUESTION Question
IDI_WARNING Warning
IDI_EXCLAMATION Exclamation
IDI_HAND Hand
IDI_ERROR Error

If you designed your own icon (you should make sure you design a 32x32 and a 16x16 versions, even for convenience), to use it, specify the hInstance argument of the LoadIcon() function to the instance of your application. Then use the MAKEINTRESOURCE macro to convert its identifier to a null-terminated string. This can be done as follows:

WndCls.hIcon = LoadIcon(hInstance, MAKEINTRESOURCE(IDI_STAPLE));

The icon can be specified by its name, which would be a null-terminated string passed as lpszResourceName. If you had designed your icon and gave it an ID, you can pass this identifier to the LoadIcon() method.

The LoadIcon() member function returns an HICON object that you can assign to the hIcon member variable of your WNDCLASS object. Besides the regular (32x32) icon, the WNDCLASSEX structure allows you to specify a small icon (16x16) to use in some circumstances. You can specify both icons as follows:

INT WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
               LPSTR lpCmdLine, int nCmdShow)
{
	WNDCLASSEX WndClsEx;

	WndClsEx.cbSize      = sizeof(WNDCLASSEX);
	WndClsEx.style       = CS_HREDRAW | CS_VREDRAW;
	WndClsEx.lpfnWndProc = WndProcedure;
	WndClsEx.cbClsExtra  = 0;
	WndClsEx.cbWndExtra  = 0;
	WndClsEx.hIcon       = LoadIcon(NULL, IDI_APPLICATION);
	WndClsEx.hInstance   = hInstance;
	WndClsEx.hIconSm     = LoadIcon(NULL, IDI_APPLICATION);

	return 0;
}

Introduction to Cursors

A cursor is used to locate the position of the mouse pointer on a document or the screen. To use a cursor, call the Win32 LoadCursor() function. Its syntax is:

HCURSOR LoadCursor(HINSTANCE hInstance, LPCTSTR lpCursorName);

The hInstance argument is a handle to the file in which the cursor was created. This file is usually stored in a library (DLL) of an executable program. If the cursor was created as part of your application, you can use the hInstance of your application. If your are using one of the below cursors, set this argument to NULL.

When Microsoft Windows installs, it also installs various standard cursors you can use in your program. Each one of these cursors is recognized by an ID which is simply a constant integers. The available cursors are:

ID Picture Description
IDC_APPSTARTING App Start Used to show that something undetermined is going on or the application is not stable
IDC_ARROW Arrow This standard arrow is the most commonly used cursor
IDC_CROSS The crosshair cursor is used in various circumstances such as drawing
IDC_HAND The Hand is standard only in Windows 2000. If you are using a previous operating system and need this cursor, you may have to create your own.
IDC_HELP The combined arrow and question mark cursor is used when providing help on a specific item on a window object
IDC_IBEAM The I-beam cursor is used on text-based object to show the position of the caret
IDC_ICON This cursor is not used anymore
IDC_NO This cursor can be used to indicate an unstable situation
IDC_SIZE This cursor is not used anymore
IDC_SIZEALL The four arrow cursor pointing north, south, east, and west is highly used to indicate that an object is selected or that it is ready to be moved
IDC_SIZENESW The northeast and southwest arrow cursor can be used when resizing an object on both the length and the height
IDC_SIZENS The  north - south arrow pointing cursor can be used when shrinking or heightening an object
IDC_SIZENWSE The northwest - southeast arrow pointing cursor can be used when resizing an object on both the length and the height
IDC_SIZEWE The west - east arrow pointing cursor can be used when narrowing or enlarging an object
IDC_UPARROW The vertical arrow cursor can be used to indicate the presence of the mouse or the caret
IDC_WAIT The Hourglass cursor is usually used to indicate that a window or the application is not ready.

The LoadCursor() member function returns an HCURSOR value. You can assign it to the hCursor member variable of your WNDCLASS object. Here is an example:

INT WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
               LPSTR lpCmdLine, int nCmdShow)
{
	WNDCLASSEX WndClsEx;

	WndClsEx.cbSize      = sizeof(WNDCLASSEX);
	WndClsEx.style       = CS_HREDRAW | CS_VREDRAW;
	WndClsEx.lpfnWndProc = WndProcedure;
	WndClsEx.cbClsExtra  = 0;
	WndClsEx.cbWndExtra  = 0;
	WndClsEx.hIcon       = LoadIcon(NULL, IDI_APPLICATION);
	WndClsEx.hCursor     = LoadCursor(NULL, IDC_ARROW);
	WndClsEx.hInstance   = hInstance;
	WndClsEx.hIconSm     = LoadIcon(NULL, IDI_APPLICATION);

	return 0;
}
 

The Window's Background Color

To paint the work area of the window, you must specify what color will be used to fill it. This color is created as an HBRUSH and assigned to the hbrBackground member variable of your WNDCLASS or WNDCLASSEX variable. The color you are using must be a valid HBRUSH or you can cast a known color to HBRUSH. The Win32 library defines a series of colors known as stock objects. To use one of these colors, call the GetStockObject() function. For example, to paint the windows background in black, you can pass the BLACK_BRUSH constant to the GetStockObject() function, cast it to HBRUSH and assign the result to hbrBackground.

In addition to the stock objects, the Microsoft Windows provides a series of colors for its own internal use. These are the colors used to paint the borders of frames, buttons, scroll bars, title bars, text, etc. The colors are named (you should be able to predict their appearance or role from their name) COLOR_ACTIVEBORDER, COLOR_ACTIVECAPTION, COLOR_APPWORKSPACE, COLOR_BACKGROUND, COLOR_BTNFACE, COLOR_BTNSHADOW, COLOR_BTNTEXT, COLOR_CAPTIONTEXT, COLOR_GRAYTEXT, COLOR_HIGHLIGHT, COLOR_HIGHLIGHTTEXT, COLOR_INACTIVEBORDER, COLOR_INACTIVECAPTION, COLOR_MENU, COLOR_MENUTEXT, COLOR_SCROLLBAR, COLOR_WINDOW, COLOR_WINDOWFRAME, and COLOR_WINDOWTEXT. You can use any of these colors to paint the background of your window. First cast it to HBRUSH and assign it to hbrBackground:

INT WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
               LPSTR lpCmdLine, int nCmdShow)
{
	WNDCLASSEX WndClsEx;

	WndClsEx.cbSize        = sizeof(WNDCLASSEX);
	WndClsEx.style         = CS_HREDRAW | CS_VREDRAW;
	WndClsEx.lpfnWndProc   = WndProcedure;
	WndClsEx.cbClsExtra    = 0;
	WndClsEx.cbWndExtra    = 0;
	WndClsEx.hIcon         = LoadIcon(NULL, IDI_APPLICATION);
	WndClsEx.hCursor       = LoadCursor(NULL, IDC_ARROW);
	WndClsEx.hbrBackground = GetStockObject(WHITE_BRUSH);
	WndClsEx.hInstance     = hInstance;
	WndClsEx.hIconSm       = LoadIcon(NULL, IDI_APPLICATION);

	return 0;
}
 

The Application's Main Menu

If you want the window to display a menu, first create or design the resource menu (we will eventually learn how to do this). After creating the menu, assign its name to the lpszMenuName name to your WNDCLASS or WNDCLASSEX variable. Otherwise, pass this argument as NULL. Here is an example:

INT WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
               LPSTR lpCmdLine, int nCmdShow)
{
	WNDCLASSEX WndClsEx;

	WndClsEx.cbSize        = sizeof(WNDCLASSEX);
	WndClsEx.style         = CS_HREDRAW | CS_VREDRAW;
	WndClsEx.lpfnWndProc   = WndProcedure;
	WndClsEx.cbClsExtra    = 0;
	WndClsEx.cbWndExtra    = 0;
	WndClsEx.hIcon         = LoadIcon(NULL, IDI_APPLICATION);
	WndClsEx.hCursor       = LoadCursor(NULL, IDC_ARROW);
	WndClsEx.hbrBackground = GetStockObject(WHITE_BRUSH);
	WndClsEx.lpszMenuName  = NULL;
	WndClsEx.hInstance     = hInstance;
	WndClsEx.hIconSm       = LoadIcon(NULL, IDI_APPLICATION);

	return 0;
}

The Window's Class Name

To create a window, you must provide its name as everything else in the computer has a name. The class name of your main window must be provided to the lpszClassName member variable of your WNDCLASS or WNDCLASSEX variable. You can provide the name to the variable or declare a global null-terminated string. Here is an example:

LPCTSTR ClsName = L"BasicApp";

INT WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
               LPSTR lpCmdLine, int nCmdShow)
{
	WNDCLASSEX WndClsEx;

	WndClsEx.cbSize        = sizeof(WNDCLASSEX);
	WndClsEx.style         = CS_HREDRAW | CS_VREDRAW;
	WndClsEx.lpfnWndProc   = WndProcedure;
	WndClsEx.cbClsExtra    = 0;
	WndClsEx.cbWndExtra    = 0;
	WndClsEx.hIcon         = LoadIcon(NULL, IDI_APPLICATION);
	WndClsEx.hCursor       = LoadCursor(NULL, IDC_ARROW);
	WndClsEx.hbrBackground = GetStockObject(WHITE_BRUSH);
	WndClsEx.lpszMenuName  = NULL;
	WndClsEx.lpszClassName = ClsName;
	WndClsEx.hInstance     = hInstance;
	WndClsEx.hIconSm       = LoadIcon(NULL, IDI_APPLICATION);

	return 0;
}
 

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