Windows Basics

1
Windows Basics

• Windows is a 32 bit, preemptive, multitasking,
  multithreaded, graphical operating system.
• Preemptive multitasking multiple programs
  executing, OS time slices all programs.
• Multithreaded Program decomposed into multiple
  threads, threads are time sliced.

2
Windows

• Implemented as a set of dynamic link libraries
  (dlls).
• dlls are not loaded into executable.
• Provide the Application Program Interface (API).
• API dictates event-driven (asynchronous) program
  architecture.
• Reacts to messages sent by OS or application.

3
Program Architecture

• Logically message driven
• OS creates one message queue for application.
• Logically, OS places messages in queue.
• Application provides message loop to retrieve
  messages from queue.
• Polling for messages.
• Causes messages to be processed.
• Lots of messages sent to program, most of which
  the program does not process.

4
Program Architecture

• If interested in event specified by a message,
  provide a handler.
• Example Application receives WM_PAINT message
  every time the window needs to be updated.
• Provide handler.
• Another example Application receives a WM_NCHIT
  message every time the mouse moves onto
  non-client piece of the window.
• May receive one per pixel.
• Must provide default handler for every message
  not processed.

5
Default Message Processing

• switch(msg_type)
• case WM_PAINT // do something. Then
  return
• case WM_SIZE //do something. Then return.
• ..
• return DefWindowProc(hwnd, message, wParam,
  lParam)
• This catches all messages not caught by
  handlers.

6
Default Message Processing

• Default processing normally generates other
  messages that are also sent to application.
• Such messages also processed through default
  processing function. Generates other messages,
  and so forth.
• Point There is a whole lot going on under the
  covers that the application programmer will never
  deal with.

7
Unicode

• Characters are 8 bits 256 combinations.
• Unicode extends to 16 bits 65,536 comb.
• Use TEXT(this is a string) macro.
• TCHAR Pointer to a string.
• Static TCHAR grumpy I feel grumpy

8
No Printf or Cout

• Windows does not understand sdtin, stdout.
• wsprintf(buf, format string, variables)
• char buf100
• int a,b,c
• a 10 b 2 c a b
• wsprintf(buf, The sum of a d and b d is
  d, a, b, c)
• s, c, f
• Use with TextOut function. Significantly more
  powerful than printf, cout, ..

9
Windows Programs

• All windows based on class, each class has
  exactly one message processing function.
• Provide handlers for messages of interest.
• All others handled by default processing
  function.
• Message passing is really the OS calling the
  message processing function for the window.
• Messages can be placed in message queue, or the
  OS can call window procedure directly.

10
Function Prototypes

• include ltwindows.hgt
• LRESULT CALLBACK WndProc (HWND, UINT, WPARAM,
  
  LPARAM)
• Int WinAPI WinMain(HINSTANCE hInstance,
• HINSTANCE hPrevInstance,
• PSTR szCmdLine,
• int iCmdShow)

11
Variable Declarations

• static TCHAR szAppName TEXT(HelloWin)
• HWND hwnd
• MSG msg
• WNDCLASS wndclass

12
Fill in Class Characteristics

• wndclass.style CS_HREDRAW CS_VREDRAW
• wndclass.lpfnWndProc WndProc
• .
• wndclass.hInstance hInstance
• wndclass.hIcon LoadIcon(NULL,
  IDI_APPLICATION)
• wndclass.hCursor LoadCursor(NULL, ID_ARROW)
• wndclass.hbrBackground (HBRUSH)
• GetStockObject(WHITE_BRUSH)
• wndclass.lpszClassName szAppName

13
Register Class

• if (!RegisterClass (wndclass))
• MessageBox (..)
• return 0

14
Create Window

• hwnd CreateWindow(szAppName, //set above
• TEXT(The Hello Program), //caption
• WS_OVERLAPPEDWINDOW, //style
• CW_USEDEFAULT, // initial x
  
• CW_USEDEFAULT, // initial y
• CW_USEDEFAULT, // initial x size
• CW_USEDEFAULT, // initial y size
• NULL, //parent window handle
• NULL, // window menu handle
• hInstance, // program instance
  handle
• NULL // creation parameters)

15
Lab 2

• Declare an array of size WM_USER to track
  messages sent but not processes.
• Element 0 of array tracks number of messages of
  type 0 (if message 0 is not processed by
  application), element 1 tracks number of messages
  of type 1and so forth.
• Print out the top 5 such messages.
• Scan the array (at least) 5 times to pick out
  max.
• Have to trap WM_CLOSE message as discussed on Web.