Win32API Interview Questions And Answers

Win32 refers to Microsoft 32 bit Windows API. Win32
Applications are programs which are built with the Win32
API.

Should be LibMain in win3.1

But WinExec() is compatible with 16-bit Windows.
Applications should use the CreateProcess
function.http://msdn.microsoft.com/en-us/library/ms687393(VS.85).aspx

Win3.1 supports co-operative multi-tasking. Once a process
is given the control for execution, the other tasks have to
wait until the current has relinquished its execution.

WinNT is preemptive multi-tasking. A process can be stopped
in the middle if another process needs CPU cycle.
This is handled by the windows OS.

It evolved like this
when u write a CLASS to reuse in a application, multiple
intances of the class exists with each instance of
application,
Next u want to avoid it so u make a class and put it in DLL
now only one instance exists though multiple instances of
applications exists
Applicatoin needs to be recompiled whenever Dll is
modified, SO came COM.
COM is independent component that internally handles
networking, resources etc, COM uses IDL to communicate to
different languages

In MFC, the contents of a dialog are initialized if they are
associated with their corresponding data members. This is
done through "UpdateData(FALSE)" function. The control data
is transferred to the data members through "UpdateData(TRUE)".

In WIN32, the dialog data in controls can be initialized
during WM_INITDIALOG call. The control data can be updated
to the dialog members using apppropriate "SendMessage"
functions.

Win32 is a set of Windows APIs written in C and MFC is a
framework built arround Win32. All MFC functions internally
use Win32 APIs. And MFC is written in C++.

It uses main three patterns,
Singleton pattern - Application object(CWinApp & its
derived classes)
Bridge pattern - Serialization
Observer patten - Document/View Architecture

If we dig deeper into the MFC classes, it may use some
other patterns also.

A faik CString is a MFC class. You cannot use it in win32
application unless you set your application to use MFC
libraries. To use MFC in win32 application, go to project
settings and in general tab, set it to use MFC libraries in
shared DLL. Then you can include MFC framework files like
afxwin.h.

ShowWindow(hwnd, SW_HIDE); // to hide window
ShowWindow(hwnd, SW_SHOW); // to show window

In OnInitDialog:
-----------------
1. Create CBitmap from the bitmap.
2. Create a memory DC (CDC)
3. Put the CBitmap into the memory DC (Use
CDC::SelectObject function).


In OnPaint:
------------
4. Get your dialog DC (CDialog::GetDC)
5. Do BitBlt or StretchBlt on dialog DC with memory DC as
source DC (this will paint the bitmap on your dialog).
6. Release dialog DC (ReleaseDC function)

A faik CString is a MFC class. You cannot use it in win32
application unless you set your application to use MFC
libraries. To use MFC in win32 application, go to project
settings and in general tab, set it to use MFC libraries in
shared DLL. Then you can include MFC framework files like
afxwin.h.

Java just uses object oriented principals but it is not purely object oriented , because int is a primitive data type in Java but not an object similarly all primitive data types a pure object oriented language should not support a non object oriented aspects

reateWindow() physically creates the Window in memory
based on the previousy registered WNDCLASS structure and
returns a vaild HANDLE for that Window

Pre emption is releasing the process in order to serve
another process to utilize the same resource. Context
switching is the transfer of resource from once process to
another process.

WM_QUIT message in the program message queue is posted.
This causes WinMain to drop out of message loop and exit
the runing application.

SendMessage is a blocking call. ie., when a SendMessage()
API is called from an application, the lines written after
this API call cannot be executed until the message is
processed and returned by the window procedure.

Whereas PostMessage() just posts the message into the
windows corresponding message queue and returns immediately
irrespective of the message is processed or not.

Invalidate() -- To repaint the entire client area
InvalidateRect() -- To repaint a specific portion of the
client area.

BOOL MoveWindow(
HWND hWnd, // handle to window
int X, // horizontal position
int Y, // vertical position
int nWidth, // width
int nHeight, // height
BOOL bRepaint // repaint option
);

This cud be used in the WM_PAINT event section and in
WM_INITDIALOG section.

WM_SIZE message is received by the window procedure when a
user resizes a window. In order to limite the size of a
window, you could handle the WM_SIZE message appropriately.

GDI object (is a graphical device object) used to write on a
device context for graphical output.
GDI objects are: Pen, Brush, Font,Line, Rectangle etc.
These objects are created using their corresponding win32
function. For eg, CreatePen, CreatePenIndirect are used to
create a pen object.
After these objects are created they would need to be
selected to the device context before processing using
"SelectObject" function.
GDI objects are not associated with any device context
during its creation. SelectObject function does that
assocaition.
Once an object is selected into the device context it would
be available until the object is destroyed through
DeleteObject or the program exits.