CompuServe Thread

You might think of C++ in two parts. First there are enhancements to the C language. These range all the way from an easy single-line comment (just start the line with //) to more elegant input/output [printf() replaced by cout, which in many cases will figure out what format is wanted for each variable]. In general, these make coding a little faster, although they don't tend to reduce the size of your final program. There are LOTS of these enhancement features. Second, you might say C++ is a "class" act; here's where it gets into object oriented stuff. If you know how C deals with structures, think along these lines: first, C++ can make certain parts of the structure "private" so that no outside code can look at these. Next, the structure can contain, not only data, but code, to handle parts of itself (especially those private bits). By the time we do all this, the "structure" may be renamed a "class". It works out this way: whereas in C, a program makes, loads, and changes a structure at will, in C++ it doesn't have access. It must make application to one of the embedded functions (say, "add an item", "find an item", "change an item", "delete an item") in order to interact with the structure (class) data. In particular, stuff like the links in a linked list will never be seen by "outside" code. And the calling program doesn't need to know everything that's in the data, or how it's organized; it just asks for what it wants. This type of Object Oriented Programming tends to encapsulate data into a separate module. Not just the data, of course: code can also be encapsulated in its own private module; C already does this to some extent with separate procedures. Trust this rather shallow outline will give you an idea of where C++ will take you. –Jim

Patrick, I couldn't even come close to the response you got from Jim. Robb

Patrick, The rest of my message was truncated by the system it seems. Here's the rest… In this case, SHAPE may have a single method (member function): area(). CIRCLE and SQUARE would inherit this (and in a real shape class, other data members and member functions too) and then ADD EXTRA data members and functions. You could derive a hundred other shape classes from SHAPE and they could all be compared to one another so long as they implemented an area function. The ideas of one class inheriting the properties of another and delaying the decision about which method to employ until run-time are very powerful. Another powerful feature in C++ is polymorphism which while not strictly OO, is great when combined with OOP. The example I just gave is a kind of polymorphism since one function can handle more than one class type implicitly. Here's a clearer example of polymorphism: suppose you want to add two strings together. In BASIC, strings are a first-class data type so you can add strings together easily. The "+" operator is said to be overloaded since you can add numbers AND strings together, ie. "+" is a polymorphic operator. In C++ it is possible to create a string class such that EVEN THOUGH STRINGS ARE NOT A FIRST-CLASS DATA TYPE IN C++, they can become so. You can overload "+" and "=" so that the following is possible: stringA = stringB + stringC You can also overload "*" to multiply matrices, etc. Jim mentioned the use of cin and cout (iostreams), which is another example of polymorphism. There are other features in C++ such as templates which allows you to create a generic stack class for example. You can later declare a stack of integers, reals, etc from a SINGLE class template. This is a kind of macro expansion facility. If you (or anyone else) would like some C++ code examples for anything mentioned above (or anything else in C++), please feel free to ask. Also, I think it's important to mention that unlike C, there is still no official C++ standard yet. The first ANSI/ISO draft standard is due to be released for public comment within the next couple of months. However, the standard C library will be included (with minor mods). I/O streams is also a part of the standard. There are differences between compilers at present which the standard will hopefully resolve down the track. Regards, David Benn (author of ACE)

Steve, OK. I'll head to the bookstore tomorrow (I've printed that out to take with me), but I'm still not convinced that C++ is really an extension to C (I know C), C++ is, definitely, a differnet way of looking at things. Robb

Wrong guy, but I can't dig up the right name or title either. — Dale L. Larson, Intangible Assets Manufacturing — INTERNET:dale@iam.com