Follow Techotopia on Twitter

On-line Guides
All Guides
eBook Store
iOS / Android
Linux for Beginners
Office Productivity
Linux Installation
Linux Security
Linux Utilities
Linux Virtualization
Linux Kernel
System/Network Admin
Scripting Languages
Development Tools
Web Development
GUI Toolkits/Desktop
Mail Systems
Eclipse Documentation

How To Guides
General System Admin
Linux Security
Linux Filesystems
Web Servers
Graphics & Desktop
PC Hardware
Problem Solutions
Privacy Policy




Thinking in C++
Prev Contents / Index Next

Abstract data typing

The ability to package data with functions allows you to create a new data type. This is often called encapsulation[33]. An existing data type may have several pieces of data packaged together. For example, a float has an exponent, a mantissa, and a sign bit. You can tell it to do things: add to another float or to an int, and so on. It has characteristics and behavior.

The definition of Stash creates a new data type. You can add( ), fetch( ), and inflate( ). You create one by saying Stash s, just as you create a float by saying float f. A Stash also has characteristics and behavior. Even though it acts like a real, built-in data type, we refer to it as an abstract data type, perhaps because it allows us to abstract a concept from the problem space into the solution space. In addition, the C++ compiler treats it like a new data type, and if you say a function expects a Stash, the compiler makes sure you pass a Stash to that function. So the same level of type checking happens with abstract data types (sometimes called user-defined types) as with built-in types.

You can immediately see a difference, however, in the way you perform operations on objects. You say object.memberFunction(arglist). This is “calling a member function for an object.” But in object-oriented parlance, this is also referred to as “sending a message to an object.” So for a Stash s, the statement s.add(&i) “sends a message to s” saying, “add( ) this to yourself.” In fact, object-oriented programming can be summed up in a single phrase: sending messages to objects. Really, that’s all you do – create a bunch of objects and send messages to them. The trick, of course, is figuring out what your objects and messages are, but once you accomplish this the implementation in C++ is surprisingly straightforward.

Thinking in C++
Prev Contents / Index Next

   Reproduced courtesy of Bruce Eckel, MindView, Inc. Design by Interspire