Windows Sockets: Deriving from Socket Classes
The latest version of this topic can be found at Windows Sockets: Deriving from Socket Classes.
This article describes some of the functionality you can gain by deriving your own class from one of the socket classes.
You can derive your own socket classes from either CAsyncSocket or CSocket to add your own functionality. In particular, these classes supply a number of virtual member functions that you can override. These functions include OnReceive, OnSend, OnAccept, OnConnect, and OnClose. You can override the functions in your derived socket class to take advantage of the notifications they provide when network events occur. The framework calls these notification callback functions to notify you of important socket events, such as the receipt of data that you can begin reading. For more information about notification functions, see Windows Sockets: Socket Notifications.
Additionally, class CSocket supplies the OnMessagePending member function (an advanced overridable). MFC calls this function while the socket is pumping Windows-based messages. You can override OnMessagePending to look for particular messages from Windows and respond to them.
The default version of OnMessagePending supplied in class CSocket examines the message queue for WM_PAINT messages while waiting for a blocking call to complete. It dispatches paint messages to improve display quality. Aside from doing something useful, this illustrates one way you might override the function yourself. As another example, consider using OnMessagePending for the following task. Suppose you display a modeless dialog box while waiting for a network transaction to complete. The dialog box contains a Cancel button that the user can use to cancel blocking transactions that take too long. Your OnMessagePending override might pump messages related to this modeless dialog box.
In your OnMessagePending override, return either TRUE or the return from a call to the base-class version of OnMessagePending. Call the base-class version if it performs work that you still want done.
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