Message Loop

Message Loop:

When the program is ready to use keyboard and mouse input from user, these inputs comes in the form of “message”. The window maintains a message queue for each program. When input event occurs, windows translate the event into message i.e. placed in the program message queue.

A program retrieves these messages from the queue by executing a block of code known as the “message loop”.

while(GetMessage(&msg,NULL,0,0))

{

 TranslateMessage(&msg);

 DispatchMessage(&msg);

}

1.     GetMessage:

The GetMessage call begins the message queue. The second, third, fourth arguments are set to NULL or 0 to indicate that program wants all messages from program.

If the message field of the message retrieve from the message queue as anything except WM_QUIT, GetMessage returns a non-zero value.

2.     TranslateMessage:

TranslateMessage takes responsibility of translating key stroke message to character message.

3.     DispatchMessage:

DispatchMessage pass the message structure to WndProc. After the WndProc process the Message, it returns the control to window. The message loop continue with the next message call.