- What is meant by SDK
It’s an acronym for Software Development kit. It is a set of tools designed to help C programmers to create windows applications. The Windows SDK consist of the following elements:
a) A large set of books describing functions, messages,structures, macros and resources
b) Various tools including a dialog editor and an image editor.
c) On-line help files
d) A set of windows libraries and header files
e) Sample windows programs in C.
- What is an API?
API is an acronym for Application Programming Interface. It is simply a set of functions that are part of Windows OS. Programs can be created by calling the functions present in the API. The programmer doesn’t have to bother about the internal working of the functions. By just knowing the function prototype and return value he can invoke the API functions. A good understanding of Windows API would help you to become a good windows programmer. Windows itself uses the API to perform its amazing GUI magic. The Windows APIs are of two basic varieties:
-API for 16 bit windows
-API for 32 bit windows
- Define Window Class
A window class is a template, or plan, for creating a number of windows with
Similar characteristics. When we create a window class we specify certain attributes the window will have, such as what mouse cursor will appear in the window, what icon will appear when the window is minimized, and the menu structure it will use. Then we use this class as a blueprint to create actual windows that have these attributes.
typedef struct tagWNDCLASS
{WORD style;
LONG (FAR PASCAL *lpfnWndProc)();
int cbClsExtra;
int cbWndExtra;
HANDLE hInstance;
HICON hIcon;
HCURSOR hCursor;
HBRUSH hbrBackground;
LPSTR lpszMenuName;
LPSTR lpszClassName;
} WNDCLASS;
- What is meant by Registering the Class or Window Registry
Once a window class has been specified by assigning values to the fields of the wndclass variable, and we have to inform to the Windows to store this information in memory. The RegisterClass() function does this.
RegisterClass (&wndclass);
This function takes as its only argument the address of the structure defining the class. Windows knows about the the specification of the windows variable.
If the previous instance of the application already active, there’s no need to register the window class a second time. If this is the first instance of the application the class definition must be assigned and the window class registered.
- Define Message
A message is a small unit of information. A message is sent by windows to an application’s window any time an event takes place that affects the application. A message consists of information like “the user clicked the left moust button with the pointer at coordinates” or “the user pressed the key” .
Windows transmits a message to an application by calling a function in that application. Transmitting a message means calling a function. A window is a key unit of program organization in Windows. There is one message receiving function associated with each window class.
- What is meant by Device Context
The concept of device context is used to provide the connection between windows’ graphics functions and the “real world’ of computer hardware. Windows programs can use the same graphical functions, such as Textout(), and Rectanlge() to output to any device context. Windows handles the chore of translating the function calls into commands that a printer, plotter, or video board will understand. The handy feature of the device context is the ability to describe the output surface such as screen, printer page etc. with different sets of units.
- What is a handle?
A handle is simply a number that refers to an entity. The entity could be a window, an icon, a brush, a cursor, a file or any such entity. The handles in windows are similar to the file handles used in conventional C and MS-DOS programming.
- what do you mean by DLL?
DLL stands for Dynamic link libraries. A DLL is a binary file that provides a library of functions, objects and resources. All the API functions are contained in Dynamic link libraries. The functions present in DLLs can be linked during execution. These functions can also be shared between several applications running in Windows. Since linking is done dynamically the functions do not become part of the executables files. As a result, the size of the EXE files do not go out of hand. It is also possible to create our own DLLs. The reason for having own DLLs is
- sharing common code between different executable files
- Breaking an application into component parts to provide a way to easily upgrade application’s components.
- Keeping resource data out of an application’s executable, but still readily accessible to an application.
9. What is Hungarian Notation?
Hungarian Notation is a variable naming convention so called in the honour of the legendary Microsoft programmer Charles Simonyi. According to this convention the variable name begins with a lower cse letter or letters that denotes the data type of the variable. For eg., the sz prefix in szCmdLine stands for ‘string terminated by zero’; the prefix h in hInstance stands for “handle”; The naming conventions might make the code more readable to other windows programmer who do.
| Prfix | Data Type |
| C | Char |
| By | BYTE |
| N | Short |
| I | Int |
| B | BOOL |
| W | WORD |
| H | handle |
10. Discuss about the structure of a Windows program or Overview of Windows programming
Windows program basically does 2 things;
- Perform initial activities when the program is first loaded into memory. These activities consist of creating the program’s own window and startup activities, such as setting aside some memory space.
- Process messages from windows
The key item in the first step is creating the program’s window, which is the piece of the screen that the program will control. Application program only write inside their own window, not in other program’s windows or on the background of the screen. Restricting output to the program window is one of the keys to having several programs coexist on the same screen. Program windows are always rectangular and may contain different elements such s menus, bitmaps, dialog boxes, etc. depending upon what the program does. The client area of the window is the central portion in which the program can draw graphics and text. When a program’s window is visible, it will just wait until windows sends the program a message. The waiting is accomplished by a program loop, called the message loop.
11. What do you mean by Device Context
During the original design of windows, one of the goals was to provide “device independence”. Device independence means that the same program should be able to work using different screens, keyboards, and printers without modification to the program. Windows takes care of the hardware, allowing the programmer to concentrate on the program itself. Windows programs do not send data directly to the screen or printer. Instead the program obtains a handle for the screen or printer’s device context. The output data is sent to the device context and then wnindows takes care of sending it to the real hardware. The advantage of using the DC is that the graphics and text commands sent to the DC is always the same.
12. Define Windows GDI
The part of the Windows that converts the windows gaphics function calls to the actual commands sent to the h/w is the GDI or Graphics Device Interface. The GDI is a program file called GDI.EXE that is stored in the Windows system directory. The Windows environment will load GDI.EXE into memory when it is needed for graphical output. Windows will also load a “Device Driver” program if the hardware conversions are part of GDI.EXE. Drivers are just programs that assist the GDI in converting windows graphics commands to hardware commands.
13. List out the predefined windows Constants
Windows also uses an extensive list of predefined constants that are used as messages, flag values, and other operational parameters. These constant values are always full uppercase and most include a two or three letter prefix set off by an underscore. Eg:
CS_HREDRAW CS_VREDRAW CW_USERDEFAULT
DT_CENTER DT_SINGLELINE DT_VCENTER
IDC_ARROW IDI_APPLICATION WM_DESTROY
WM_PAINT WS_OVERLAPPEDWINDOW
The prefixes indicate the general category of the constant.
Prefix Category
CS Class style
CW Create Window
DT Draw Text
IDC Cursor ID
IDI Icon id
WM Window Message
WS Window style
14. Discuss about the Data types and Data structures in Windows
Windows use wide variety of new data types and type identifies most of which are defined in either the WinDef.H or WinUser.H header files.
DATA TYPE MEANING
FAR Same as far. Identifies an address that originally used the
Segment:offset addressing schema. Now FAR simply identifies 32bit address but may be omitted entirely in many cases
PASCAL Same as pascal. The pascal convention demanded by Windows
Defines the order in which arguments are found in the stack when passed as calling parameters
WORD unsigned integer(16 bits)
UINT unsigned integer, same as WORD
DWORD Double word, unsigned long int(32 bits)
LONG Signed long integer(32 bit)
LPSTR Long (far) pointer to character string
Data Structures
Windows adds a variety of new data structures.
| Structure | Example | Meaning |
| MSG | msg | Message Strurcture |
| PAINTSTRUCT | ps | Paint structure |
| PT | pt | Point Structure |
| RECT | rect | Rectangle structure, two coordinate pairs |
| WNDCLASS | wc | Window class structure |
15. List out the resources available in Windows programming
- Accelerator
- Bitmap
- Cursor
- Dialog
- Icon
- Menu
String Table
13. What is meant by Virtual Key code?
Virtual key codes are one of the ways Windows makes sure that a program written for one type of computer keyboard will function properly on another type.
The values that passed as the wParam parameter with WM_KEYDOWN and WM_KEYUP messages are as follows
Virtual Key Code Value Meaning
VK_ACCEPT 0x1E
VK_ADD 0x6B Plus key
VK_BACK 0x08 Back space
VK_CLEAR 0x0C Clear key
VK_END 0x23 End
14. What do you mean by Event driven programming?
Event driven simply means that every part of the OS communicates with every other part and with applications through windows messages. Events occur in response to message being passed between windows and in response to user interaction with the OS and applications. One of the major job as a windows programmer is to respond to those events. While programming for Windows the OS not only executes the program, it talks to it! And the application talks back.
In the event driven programming model the application on execution sets p variables and structures and perform other initializations just as a typical procedural program does. Once this initialization phase is over the activity ceases. The windows application sits there, waiting for user input of some form or the other. This input can be in the form of a mouse click or a keystroke. As soon as the user provides this input, a series of events follows, and the application responds to these events.
15. What are Queued and Non Queued Messages
In the event driven programming model that Windows is based on. Windows sends numberous messages to the application. For example, a message is sent when the window is first being created. Messages are also sent when a menu item is clicked or the window is moved or the window is resized etc.
A windows program has a message loop that retrieves messages from the message queue by calling the GetMessage() function and dispatches them to the window procedure by calling DispatchMessage() function.
The messages which are sent to the application by directly calling its window procedure are called nonqueued messages. The messages that posted to the queue is called queued message. Non queued messages are sent to the window procedure. Keyboard messages, mouse messages, timer messages are the queued messages. All other messagaes are non queued messages.
16. What is MFC?
MFC is the c++ class library Microsoft provides to place an object
oriented wrapper around the Windows API. CWnd class encapsulates the functionality of a window. In an MFC program, we rarely need to call the Windows API function directly. Instead , we create objects from the MFC classes and call member functions belonging to those objects. Many of the hundreds of the member functions defined in the class library are thin wrappers around the Windows API and even have the same names as the corresponding API functions.
MFC is an application framework. MFC helps define the structure of an application and handles many routine chores on the application’s behalf. Starting with CwinApp, the class that represents the application itself, MFC encapsulates virtually every aspect of a program’s operation. The framework supplies the WinMain() function, and WinMain() in turn calls the application object’s member functions to make the program go. One of the CwinApp member function called by WinMain() is Run() function that encapsulates the message loop that literally runs the program.
17. What are the series of actions that take place when I try to close a window?
When we try to close an application by clicking on the close button, a WM_CLOSE message is sent our application. If we do not handle this message then it is passed to the default window procedure. The default window procedure destroys the window by calling the ::DestroyWindow() API function. This function places WM_DESTROY message in the message queue of the application. Following the WM_DESTROY, there is another message called WM_NCDESTROY . In reaction to this message a handler OnNcDestroy() gets called. This handler calls another function – PostNcDestroy(). It is in this function that the ::PostQuitMessage() function is called. This function places a message WM_QUIT in the message queue. When this message is retrieved, the message loop is terminated. This ultimately leads to termination of the application.
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