TweetFollow Us on Twitter

C++ Overview
Volume Number:5
Issue Number:9
Column Tag:Jörg's Folder

C++ Overview

By Jörg Langowski, MacTutor Editorial Staff

“An Overview Of C++”

MacHack ’89 brought me not only a colorful set of screwdrivers from APDA, but also a new assignment: yours truly is supposed to run a tutorial column on C++. C++ is a very interesting programming language. Supposedly, the new Finder was written in it. Also, it exists on a couple of Unix systems. In fact, shopping for a Unix system, we recently met a representative who assured us that C++ would be delivered with the system. Jordan Matthews, and other people from Apple, spoke very highly about C++ at the MacHack, and assured us that we would get our fingers on a pre-release of Apple’s C++ for MPW, supposedly to be delivered by the end of this year.

As you might have guessed, Apple hasn’t sent us the pre-release yet, and I have yet to use a working C++ compiler. So far my only ‘hands-on’ experience is Bjarne Stroustrup’s book, The C++ Programming Language (Addison-Wesley 1987), which I highly recommend.

The style of the book is rather terse, and you have to work your way through. A good example is that after the introduction, not much is said about ‘object-oriented’ programming, until you hit page 213:

“A list specified in terms of pointers to a class can hold objects of any class derived from that class. That is, it may be heterogeneous. This is probably the single most important and useful aspect of derived classes, and it is essential in the style of programming presented in the following example. That style of programming is often called object based or object oriented; it relies on operations applied in a uniform manner to objects on heterogeneous lists.”

So now you know what you’ve really done when you used MacApp The fact that Stroustrup refers to object-oriented programming in this rather abstract way made me dig out an old introduction to Simula 67, which was the first language to introduce object-oriented concepts. There, too (the book dates from 1973) no reference is made to OOP as we know it today. All the important constructs - classes, instances, methods, overriding - are already there, and one could have implemented today’s programming style in Simula; only computers were much smaller, and most programs did not demand OOP concepts.

The C++ Design

Stroustrup’s team designed C++ for dealing with simulation problems not unlike those that Simula was developed for. However, C++ is a much broader concept than simply a set of ‘object-oriented’ extensions to C; it is a redesign of the C language. To use another quotation from Stroustrup’s book, “C++ was designed to enable larger programs to be structured in a rational way so that it would not be unreasonable for a single person to deal with 25,000 lines of code”. To achieve such an ambitious goal, the most important point is to allow the user to extend the language to accommodate new ‘shorthand notations’ for things that have to be done over and over again. For instance, in a program that uses matrix algebra, given the 25-row by 35-column matrix C and 25-row by 15-column matrix B,

A = ^B*C

is much easier to read than

matmul (A,transpose(B),C,15,25,35).

To be able to use such a shorthand for matrix multiplication, we would need two features built into the language: a. data structures that carry additional information, such as row and column size for a matrix, but which is normally hidden to the user; and b. the capability to redefine operators - like ‘*’ or ‘^’ - depending on the context in which they are used. The latter feature would then cause a ‘*’ to behave differently depending on whether it is used to multiply two integers, reals, vectors or matrices. Some of this behavior is already built into most compilers: integer and real multiply generate different code. But this behavior cannot be modified. C++ allows you to modify your operators in any odd way.


Let’s assume we wanted to define an array structure, matrix, whose size is not defined at compile time and for which space will be dynamically allocated at run time. In C, one might write

typedef struct matrix
    int rows, cols;
    int *m;  /* pointer to matrix  data */
matrix a

and then write an indexing function elem(i,j) which refers to the (i,j)th element of the matrix a by

*(a.m + 2*(i*a.cols + j)).

Of course, it would be much easier to simply define a two-dimensional array and write a[i][j], but let’s stay with this definition for a while; unlike the usual array definition, this matrix is resizeable and space is allocated dynamically at run time. We would have to find a block of memory to hold the matrix data and put a pointer to it in m.

When we access an array, we are often not interested in its actual dimensions, as long as the indices are not out of range. In C++ we can define the matrix type in such a way that only certain functions have access to information ‘private’ to the array (such as its dimensions), and all access to the array’s data is done through these access functions, called methods. Data structures that may carry private information are called classes in C++. (According to the manual, classes are ‘user-defined types’ - the most general definition that one might imagine!). A class is just like a struct in which some of the fields cannot be ‘seen from the outside’, and in which the interface to these private fields is defined through method declarations. The C++ class definition for the matrix type would look very similar to a struct declaration, with some additions. The syntax of the class declaration is:

/* 1 */

class matrix
     int rows, cols;
     int *m;  /* pointer to matrix  data */
     int rowsize() { return rows}
     int colsize() { return cols }
     void set_size(int,int);
     int& elem(int,int);
matrix a

Those of you who have had some experience with NEON [let’s make the point again that it is a shame that NEON has disappeared ] might recall that its class definition looked similar:

:class matrix <super object
     2 <indexed
     int rows
     int cols
   :M rowsize    ;M

NEON, however, did not have the label public: for separating the private and public parts of the class declaration. In NEON, all variables were private and all the methods were public.

The C++ class declaration is similar to a C struct declaration, with the possibility to include functions and to hide parts of the declaration from the outside. The public functions in a class that constitute the interface to the outside world are called methods.

There are two principal ways to define a method. One can write the method code inside the class declaration (as for rowsize and colsize in the example above), or one can just declare the method and write the method code later, as for set_size or elem. elem returns the reference to an integer that is the (i,j)th element of the matrix and might be defined as follows:

/* 3 */

int& matrix::elem(int i, int j)  { return m[i*cols + j] };

There is a fundamental difference between methods defined inside and outside of a class declaration. The methods defined outside will be called through a subroutine call, while inside-defined methods are inline-expanded by the compiler. Writing a.rowsize will not generate a JSR to the function code, but code that will directly reference the hidden field a.row. However, any method that is defined outside a class declaration may also be defined as an inline method by prefixing it with the keyword inline:

/* 4 */

inline int& matrix::elem(int i, int j)  { return m[i*cols + j] };

There are two more special methods in the class declaration which carry the name of the class, or respectively the class name prefixed with a tilde (~). These are the so-called constructor and destructor methods; they are called when a new object is declared (as in matrix a;) or deleted (when one leaves the block that the object was declared in). Constructors and destructors are important when heap space has to be allocated for an object (our matrix will need it) and deallocated when the object is no longer defined.


Our dynamically sized matrix might be defined in a slightly different way which allows to access the elements in the usual way, writing a[i][j] instead of a.elem(i,j). One first defines a one-dimensional array class (as in Stroustrup’s book):

/* 5 */

class vector 
     int* v;
     int sz;
     vector(int); ~vector();
     int size () { return sz; }
     void set_size(int);
     int& operator[](int);
     int& elem(int i) { return v[i] };

and then builds the two-dimensional class on top of it:

/* 6 */

 class matrix : vector
     vector*& mv;
     int rows, cols;
     matrix(int,int); ~matrix;
     int rowsize () { return rows; }
     int colsize () { return cols; }
     void set_size(int,int);
     vector*& operator[](int);
     int& elem(int i, int j) { return mv[i][j] };

(I hope this is approximately correct while I’m waiting for the C++ system to try this out and get ready for your embarrassing remarks). In the program, one would declare matrix a(10,20) and access the (i,j)th element by writing a[i][j]. The array indexing operator [] has been re-declared in the class declaration, and will now support checking of index bounds, if we wish so.

The actual implementation of the operators has of course to be done separately. We would write

/* 6 */

 int& vector::operator[](int i) { /* body of code */ }


/* 7 */

 vector*& matrix::operator[](int i) { /* body of code */ }

to implement the new definitions.

The matrix multiplication operator may now be defined easily. We write

/* 8 */

matrix operator*(matrix& a, matrix& b)
     matrix c(a.colsize,b.rowsize);
     if (a.rowsize != b.colsize) error “index mismatch”;
     for (int i=1 ; i<a.colsize ; i++)
          for (int j=1 ; j<b.rowsize ; j++)
               int sum = 0;
               for (int k=1 ; k<a.rowsize ; k++)  
                    sum = sum + a[i][k]*b[k][j];
               c[i][j] = sum;
     return c;

Again, I hope this would work in an actual example. It is not the most efficient way to program the matrix multiplication; the good way to do it would be using friend definitions. This concept is explained in Stroustrup’s book, and I’m going to come back to it in the next column, where I can supply some examples.

The expression a*b, where a and b are of type matrix, would return a pointer to another object of class matrix, which contains the product of a and b. To make sense of the expression c = ^a*b, we would also have to define the transpose operator, ‘^’, and the assignment operator, ‘=’. I won’t write these definitions down here; you might try to work them out, or better, test them if you have a C++ system available.

Operator redefinition is one of the most important concepts of C++, since it makes the code much more readable. The redefinition of an existing operator (like +, *, etc.) is called operator overloading; when such a redefined operator is used, the compiler will automatically search the existing definitions to find one that works on the data types provided. Thus, even if one redefined * for matrices, integer and real multiplications would still work as before. I have not found out yet whether dynamic binding is possible for operators by declaring them virtual (see below), but I’m sure I’ll soon be able to test that.

Class Hierarchies

We have seen the syntax of a class definition which was derived from another class, class matrix : vector { }. If we define a derived class this way, none of the methods in the superclass will be accessible through an object of the subclass; all subclass methods have to be explicitly defined in the subclass declaration. If we write, on the other hand, class matrix : public vector { }, any method from class vector that is not redefined in class matrix is usable on objects of class matrix as well. This is the way we very often wish objects to behave; methods that are redefined in a subclass should override the superclass definition, but if an object does not ‘know’ about a method it should look for a definition higher up in the hierarchy.

In a class hierarchy we should therefore be able to apply a method to an arbitrary object whose exact type is not known at compile time. If the object’s type is known at compile time, the compiler will simply generate a JSR to the appropriate method code, passing arguments as required. This is known as early binding in object-oriented jargon. If the type is not known, we must check at run time what type of object is given the method call, and see whether the method is defined in the object’s class declaration or somewhere higher up in the hierarchy. This is called late binding; a run time error message will be generated if the method can’t be found for a particular object.

Late binding is important if we have a list of objects to which the same method should be applied, for instance a list of shapes - rectangles, circles, polygons - to be drawn on a screen. If the list is kept in an array shapelist[i], we could then simply write

/* 9 */

for (i=1;i<=N;i++) shapelist[i].draw;

to draw all the objects. This is very similar to Object Pascal, where we would write analogously


for i :=1 to N do shapelist[i].draw;

However, in Object Pascal late binding is always used when early binding can’t be applied. In C++, we have to tell the compiler that a method could be used for late binding by declaring it virtual:

/* 11 */

class TShape {
    TShape* Next, Prev;
    Rect boundRect;
    RgnHandle ShapeRgn;
    virtual void Create(rect *theRect); 
    virtual void Track(rect *oldRect,*newRect);
    virtual void Draw();
    virtual void Erase();
    virtual void Free();

This is the generic definition of a shape for which methods for drawing, erasing, etc. exist, but may or may not be defined in the top class; they may be overridden in the descendant classes, and the actual binding may be known only at run time. The figure illustrates the definition of a class hierarchy of shapes in C++ and in Object Pascal.

This more or less concludes my quick overview of the main characteristics of C++ (of course, all the features of C are still present in the language). Don’t laugh at the mistakes that are probably still in the examples; this happens when one writes programs without a compiler. There are many details I haven’t gone into here; we’ll get to know them in the following columns, with corresponding examples. Forth friends, don’t despair; you’ll get your share soon again, too.


Community Search:
MacTech Search:

Software Updates via MacUpdate

Luminar 1.2.1 - Powerful, adaptive, conf...
Luminar is the new full-featured image editor that adapts to the way you edit photos. Over 300 essential tools to fix, edit, and enhance your photos with comfort. The future of photo editing is here... Read more
1Password 6.8.1 - Powerful password mana...
1Password is a password manager that uniquely brings you both security and convenience. It is the only program that provides anti-phishing protection and goes beyond password management by adding Web... Read more
EtreCheck 3.4.4 - For troubleshooting yo...
EtreCheck is an app that displays the important details of your system configuration and allow you to copy that information to the Clipboard. It is meant to be used with Apple Support Communities to... Read more
GarageSale 7.0.8 - Create outstanding eB...
GarageSale is a slick, full-featured client application for the eBay online auction system. Create and manage your auctions with ease. With GarageSale, you can create, edit, track, and manage... Read more
Backblaze - Online backup serv...
Backblaze is an online backup service designed from the ground-up for the Mac. With unlimited storage available for $5 per month, as well as a free 15-day trial, peace of mind is within reach with... Read more
Parallels Desktop 13.0.0 - Run Windows a...
Parallels allows you to run Windows and Mac applications side by side. Choose your view to make Windows invisible while still using its applications, or keep the familiar Windows background and... Read more
Mellel 4.0.0 - The word processor for sc...
Mellel is the leading word processor for OS X and has been widely considered the industry standard for long form documents since its inception. Mellel focuses on writers and scholars for technical... Read more
Adobe Muse CC 2017 2017.1.0 - Design and...
Muse CC 2017 is available as part of Adobe Creative Cloud for as little as $14.99/month (or $9.99/month if you're a previous Muse customer). Adobe Muse 2017 enables designers to create websites as... Read more
WhatsApp 0.2.5862 - Desktop client for W...
WhatsApp is the desktop client for WhatsApp Messenger, a cross-platform mobile messaging app which allows you to exchange messages without having to pay for SMS. WhatsApp Messenger is available for... Read more
WhatsApp 0.2.5862 - Desktop client for W...
WhatsApp is the desktop client for WhatsApp Messenger, a cross-platform mobile messaging app which allows you to exchange messages without having to pay for SMS. WhatsApp Messenger is available for... Read more

Radiation City (Games)
Radiation City 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Radiation City Welcome to the world of Radiation City where a great survival adventure awaits you! | Read more »
The best deals on the App Store this wee...
The summer is drawing quickly to a close, but luckily there's a game for every season. It's an excellent week for some bargain shopping if that's what you're after. There are some big names and indie darlings in this week's roundup. It's a great... | Read more »
KORG iMono/Poly (Music)
KORG iMono/Poly 1.0.0 Device: iOS Universal Category: Music Price: $19.99, Version: 1.0.0 (iTunes) Description: *** Special Sale for a limited time to celebrate the debut of KORG iMono/Poly (33% OFF) until Sep 30! *** Reviving a... | Read more »
Super Phantom Cat 2 beginner's guid...
Super Phantom Cat 2 presents a whole new world of fun platforming challenges and perplexing puzzles. It's a well-designed platformer with a bright, neon aesthetic that brings the genre up to date. [Read more] | Read more »
Shadow Fight 2 Special Edition (Games)
Shadow Fight 2 Special Edition 1.0.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0.0 (iTunes) Description: ** New story chapter! **** No Ads! **** No energy! ** The best fighting series on mobile has returned and... | Read more »
4 RPGs like Final Fantasy XV that deserv...
Square Enix announced another Final Fantasy XV spin-off today - Final Fantasy XV Pocket Edition. This mobile, episodic version of the hit RPG gives the game a chibi-fied makeover. The first episode will be free, followed by 9 more premium episodes... | Read more »
Guild sieges and soul gems in latest upd...
Webzen’s MU Origin hit app stores last year, giving fans of fantasy hack-n-slash MMOs like Diablo a new fix to fixate on. This latest update introduces a competitive guild battle, a fresh dungeon challenge, a mini-game and some elemental gems to... | Read more »
Little Red Lie (Games)
Little Red Lie 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: ARE YOU MORE AFRAID OF POVERTY THAN DEATH? Little Red Lie is a narrative-focused, interactive fiction experience that reduces... | Read more »
You can now apply to be Clash of Clans...
Earlier this month, word got out that the Builder, the trusty handiman who tirelessly built every single building inevery singleClash of Clansbase had called it quits. Sick of seeing his work destroyed endless, the Builder has set out for our world... | Read more »
Meshi Quest beginner's guide - how...
Meshi Quest is Square Enix's newest free-to-play release, and it's a real charmer. You start off as the head of a sushi restaurant, upgrading your food and equipment as you serve visitors heaping helpings of your delicious meals. As you progress,... | Read more »

Price Scanner via

Low Cost Subscription Graphics App Alternativ...
I’m not a fan of the subscription software model, I don’t use any subscription apps. Used to be that you paid your license fee and the app was yours to use indefinitely, or until one opted for a paid... Read more
Clearance 2016 13-inch MacBook Airs, Apple re...
Apple has Certified Refurbished 2016 13″ MacBook Airs available starting at $809. An Apple one-year warranty is included with each MacBook, and shipping is free: – 13″ 1.6GHz/8GB/128GB MacBook Air: $... Read more
2017 13-inch MacBook Airs on sale for $100 of...
B&H Photo new 2017 13″ MacBook Airs on sale today for $100 off MSRP, starting at $899: – 13″ 1.8GHz/128GB MacBook Air (MQD32LL/A): $899, $100 off MSRP – 13″ 1.8GHz/256GB MacBook Air (MQD42LL/A... Read more
Sale! 13-inch 2.3GHz MacBook Pros for $100 of...
B&H Photo has 13″ 2.3GHz MacBook Pros in stock today and on sale for $100 off MSRP including free shipping plus NY & NJ sales tax only: – 13-inch 2.3GHz/128GB Space Gray MacBook Pro (MPXQ2LL... Read more
2016 MacBook Pros, Apple refurbished, availab...
Apple has Certified Refurbished 2016 15″ and 13″ MacBook Pros available starting at $1189. An Apple one-year warranty is included with each model, and shipping is free: – 15″ 2.7GHz Touch Bar Space... Read more
Apple offers Certified Refurbished iPhone 6s...
Apple has Certified Refurbished unlocked iPhone 6s’s and 6s Plus’s available starting at $449. An Apple one-year warranty is included with each phone, and shipping is free: – 16GB iPhone 6s: $449, $... Read more
Apple offers Certified Refurbished Pencils fo...
Apple has Certified Refurbished Apple Pencils available for $85 including free shipping. Their price is $14 off MSRP, and it’s the lowest price available for a Pencil. Read more
2016 15-inch 2.6GHz Touch Bar MacBook Pro ava...
B&H Photo has clearance 2016 15″ 2.6GHz MacBook Pros in stock today and on sale for $500 off original MSRP. Shipping is free, and B&H charges NY & NJ sales tax only: – 15″ 2.6GHz Touch... Read more
21-inch 2.3GHz iMac on sale for $999, save $1...
Amazon has the new 2017 21″ 2.3GHz iMac (MMQA2LL/A) in stock and on sale for $999.99 including free shipping. Their price is $100 off MSRP, and it’s the lowest price available for this model. Read more
Free Instant Translator 2.0 App For iOS Relea...
Mobile application development company, Neoappz has announced the release and immediate availability of Instant Translator 2.0 for iOS devices. Instant Translator is a user-friendly application which... Read more

Jobs Board

*Apple* Solutions Consultant - Apple Inc. (U...
Job Summary As an Apple Solutions Consultant, you'll be the link between our future customers and our products. You'll showcase your entrepreneurial spirit as you Read more
*Apple* Solutions Consultant - Apple Inc. (U...
…about helping others on a team while also delighting customers? As an Apple Solutions Consultant (ASC), you will discover customers needs and help connect them Read more
Sr. Software Engineer, Core Services, *Apple...
…part of the server team that powers various features within the App Store, Apple Music, iBooks, iTunes, and Podcasts. You will be working cross functionally with Read more
SW Engineer *Apple* TV Frameworks - Apple I...
Job Summary The Apple TV team is looking for a software engineer to join us as we work to define the future of the tvOS platform. Key Qualifications You're Read more
*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.