Chp 16: C Under Windows

Question 1

Microsoft categorizes the diff versions under 2 major heads. they?

Answer 1

Consumer Window:
For home, small offices.
Like: Windoes 95,98,ME.

Windows NT family:
For Business users.
Like: Windows NT, 2000, XP, Server 2003

Book refers to Windows NT.

Question 2

Integers under 16 bit environment and 32 bit environment:

Answer 2

In 16 bit: Int is 2 bytes

32 bit envio : Int is 4 bytes.
range -2 147 483 648 to +2 147 483 647

If we want to store age, which doesn’t need 4 bytes at all then short int [2 bytes] used. Here Int and long int is the same.

Question 3

typedefs USE:

Answer 3

1. A windows program is required to perform plenty of complex tasks, perform I/O, send mails, play sound files…etc. Using normal int data type to represent variables that hold different entities we would soon lose track of what that integer value actually represents hence typedefine the integer as COLORREF, HANDLE, BOOL,..etc
2. Typedefining long structure names.

Microsoft has done several typedefs for commonly used entities, all are stored in header files. These header files are provided as a part of 32-bit compiler like Visual C++.

Question 4

Pointers in 32 bit World:

comment on how many tasks are allowed and how are allowed tasks managed?

Answer 4

In 16 bit envio only one task could be performed at a time so single-tasking envio, so all the resources of machine, like memory and hardware devices were accessible to this program.

In 32 bit envio several program reside and work in memory at same time, multi tasking environment.
To avoid the conflict of 2 programs, windows does not permit any application direct access to any machine resource. study in “Memory Management and Device Access”

Question 5

Memory Management:

Users have become more demanding…

and windows run several applications simultaneously…

How does 16-bit envio do and how does 32 bit envio do?

Answer 5

16-bit envio allows max 1 MB which is too small for above. Hence windows evolved.
Windows run on 32-bit microprocessors so each CPU register is 32 bit long.
When we store a value at memory location the address of this location has to be stored in the register at some point of time. Thus 32 bit address can be stored in these registers and it leaves us with 2 raise 32 unique address choices. Which enables us to allow 4 GB of memory, and pointers who store these address become 4 byte entity.

Question 6

If we decide to install 4 gb, it would cost a lot. So how does windows manage?

Answer 6

Windows uses a memory model which makes use of as much of physical memory(128 MB ish..) as has been installed and simulates the balanced amount of memory on the hard disk when the need to do so arises. This memory management is demand-based.

Question 7

what do you think of the following sentence:

“ Programs are executed straight away from hard disk”

Answer 7

Programs are first brought into physical memory before they can get executed.

Question 8

Page Out operation and Page In Operation:

Answer 8

Suppose there are multiple programs in memory and new one starts executing, if this needs more memory than available then some of existing programs(or their parts) are transferred to the disk in order to free the physical memory to accommodate new program.
This operation is called page out.
When the part of pragram which was paged out is needed is brought back to memory its called page in. These both keep on happening.
Page as in a block of memory ( 4096 bytes).

Question 9

some rules sorta about page operations:

Answer 9

1. Part of the program that is being executed can be paged out to disk.
2. When it would be paged in again on need, its not necessary that it would page in at the same physical location.

Question 10

Now, how do these paging operations affect our programming:

Answer 10

Pointer hold virtual address of location.

Question 11

What is a virtual address?

Whats needed to get to an actual physical address.

Answer 11

this has 3 parts, these parts in conjunction with a CPU register (CR3) and contents of 2 tables Page directory and page table leads to an actual physical address.

Question 12

how can we get to an actual physical address?

Answer 12

CR3 holds physical location of page directory table.

Left part of 32 bit virtual address holds index to page directory table, the value at index is starting address of page table.

Middle part is index into the page table, value at this index is starting address of the physical page in memory.

The right part holds byte offset(from start of the page) of the physical memory location to be accessed.

Question 13

Can the actual address be reached by an application?

Answer 13

CR3 register is not accessible from an application, So no.

Also, as paging activity is going on the OS would suitably keep updating the values in the two tables.

Question 14

Device Access:

Answer 14

All devices are shared among all running programs, so no program can access it directly.
Access is routed through device driver program, which finally accesses the device. more in chp 17 bout the std way.
These device drivers are to make sure no conflicts occur as many programs will want to access the device.

Question 15

DOS programming Model:

Answer 15

16 bit program envio like DOS use sequential programming model. The path along which program flows from start to finish may vary during each execution depending on the inputs received or conditions under which it is run. However path remains predictable. Assume inputs to walk through program start to end.

C programs written in this model begin execution with main().

In this model the program and not the OS that decides which function will get called and when.

Question 16

Under DOS model when does program ask help from OS?

Answer 16

TO carry out jobs like console I/o, file I/o, printing..etc.

Question 17

Under Dos Model
Who performs foll operations:
Generating Graphics
Carrying out serial Communication..etc

Answer 17

The program calls another set of functions called ROM BIOS functions.

Question 18

How to call DOS and BIOS functions:

Answer 18

Unfortunately these functions do not have any names, so a mechanism called interrupts is used to call them.
Ugly: remember interrupt numbers for calling diff funcs.
And communication to these function has to be done using CPU registers, this leads to difficulties as different funcs use different registers for communication.

Providing library functions reduce these difficulties to an extent. But lib doesn’t have parallel function for every DOS/BIOS function. DOS func either call BIOS func or directly access the hardware.

Sometimes the programs are needed to directly interact with the hardware. cuz either there are no DOS/BIOS func to do so, or if their reach is limited.

Question 19

Limitations Of the DOS Model:

Answer 19

1. No true Reuse: called lib funcs become part of .exe, same functions get replicated in several EXE files, wasting disk space.
2. Inconsistent Look and feel: DOS/Bios doesn’t provide any functions for creating user interface elements like menus. So every DOS program is diff and user takes time to get comfy in using it.
3. Messy Calling Mechanism:
   There is always a chance of error while using interrupt number and registers.
4. Hardware Dependency :
   DOS programs are required to bother bout the details of the hardware, as every new hardware has it’s own interrupt number and new register details. So lot of writing to detect the hardware, this leads to large program and the programmer has to learn technical details of hardware.

Question 20

Windows Programming Model:

what new changes are observed?

Answer 20

1. Change from text interface to graphical user interface.
2. Windows OS can simultaneously execute several programs.
3. Eliminate Messy calling.
4. Permit true reuse.
5. Provide a consistent look and feel.
6. Eliminate hardware dependency.

Question 21

Windows Programming Model Calling Mechanism:

Answer 21

Instead of using Interrupt Number and registers Windows provides functions within itself which can be called using their names. These functions are called API ( Application Program Interface) functions. They help an application to perform various tasks such as creating a window, drawing a line, performing file Input/Output,..etc

Question 22

Windows Programming Model:

True reuse?

Answer 22

API files are stored in special files with extension .DLL.
DLL : Dynamic Link Libraries, its a binary file that provides a library of functions. These can be linked during execution. And can also be shared between several applications running in Windows. Since linking is done dynamically so they don’t become a part of .exe and hence size stays in hand.

Question 23

Why would you want to create your own DLL?

Answer 23

1. Sharing a common code between different executable files.

2. Breaking an application into component parts to provide a way easily to upgrade applications components.

Question 24

3 DLLs that windows API come in?

Answer 24

1. USER32.DLL : Contains function responsible for windows management like menu, cursor, communication,timer..etc
2. GDI32.DLL : Graphics. Drawing and painting.
3. KERNAL32.DLL : handle memory, management, threading, etc.

Question 25

Windows Programming Model:

Consistent Look and feel:

Answer 25

Every program has similar user interface, user doesn’t spend long time mastering a new program.
Every program occupies a rectangular area, title bar, info too large to fit on screen can be accessed using a scroll bar.
Most program functions are initiated through the program’s menus.

In almost every program there is a same dialogue box to open a file, invoked from same menu option.

Question 26

How is this consistent look possible?

Answer 26

Cuz windows rather than program handles it.

It results from using the windows API functions for constructing menus and dialog boxes.

Question 27

Windows Programming Model:

Hardware independent programming:

Answer 27

Windows program can call Windows API functions. Thus an application can communicate with
The new thing in windows is that OS can also communicate with an application.

When an event occurs, device driver informs windows, windows notifies application [ this notification is called message]. On receiving the messages the app communicates back with the OS by calling a windows API to perform the func and API will communicate with device driver requires and perform function.

Now replacing the keyboard/mouse would not affect the application. As there’s no direct communication between app and hardware.
Device driver may require changes but never in the application.

Question 28

Event?

Answer 28

The key press, mouse click are examples of event.

Question 29

Event Driven Model:

Answer 29

The order of calling the functions in the program is dictated by the order of occurrence of events in ‘Event Driven Programming Model’.

We can only anticipate what users are likely to do with app’s user interface, we can not expect what user can really say.

Question 30

Windows Programming a closer look:

How does the application process many messages ?

Answer 30

The messages are put in a queue. The messages in this queue are processed in First In First Out (FIFO) order.

Question 31

More on the queue’s maintained by OS:

Answer 31

System Message Queue: Common for all apps.
device driver sends a message to this on the occurrence of an event. After which OS finds out regarding which app and sends a message into
Application Message Queue (There is one queue per app.)
Recall the image in text. page 563.

Question 32

The first Windows Program:

Answer 32

#include 
int \_\_stdcall WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpszCmdline, int nCmdShow)
{
MessageBox(0, "Hello!", "Title",0);
return (0);
}

Question 33

Explain the Program:

Answer 33

C under windows program begins execution with WinMain().
__stdcall before WinMain indicates standard calling convention. __cdecl is another. Both pass arguments right to left. Std call stack cleaned by called function, cdecl stack cleaned by calling func.
cdecl is assumed.

Question 34

WinMain() function explanation:

Answer 34

It receives 4 params.
HINSTANCE(unsigned int) and LPSTR (pointer to a char) are typedefs.
Parameters:
hInstance : This is the ‘Instance Handle’ for the running application. Windows creates this ID number when the application starts. Used in windows func to identify data. handle is 32-bit number.
There is a unique handle for each entity and we can refer and reach them using this handle.
entity : app, window, icon, brush, cursor, bitmap, file, device.

hPrevInstance: This always contain 0, remnant of earlier version, used only for backward compatibility.

lpszCmdLine : Similar to argc, argv. Pointer to char string containing cmd line args passed to program.

nCmdShow : int passed to func,tells whether window created should appear minimized, as an icon, normal, or maximized when displayed first time.

Question 35

MessageBox() :

Answer 35

pops message box with title as Title and message “Hello!”.
MessageBos( 0, lpszCmdline, “Title”,0);
to print comndline args.they can be supplied from Start–>Run.
C:\ appname.exe abc def qwe
lpszCmdline points to “ abc def awe”

Question 36

GetCommandLine() :

Answer 36

To retrieve the entire command line including filename.

Question 37

Hungarian Notation:

Answer 37

Its a variable naming convention.
So called in the honor of Charles Simonyi.
It says:
Variable name begins with lower case letter or letters that denote the data type of the variable.
sz : string terminated by xero.
h : handle
n : int
lpsz : long pointer to a zero terminated string.

Question 38

Usage of Hungarian Notation:

Answer 38

It’s discouraged. Code when ported from 16 bit envio to 32 or 32 to 64 many changes req.
16 bit will have 2 byte and 4 byte int as diff datatypes
whereas in 32 there will be int of 4 byte.