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

CrossOver 14.1.6 - Run Windows apps on y...
CrossOver can get your Windows productivity applications and PC games up and running on your Mac quickly and easily. CrossOver runs the Windows software that you need on Mac at home, in the office,... Read more
Printopia 2.1.14 - Share Mac printers wi...
Run Printopia on your Mac to share its printers to any capable iPhone, iPad or iPod Touch. Printopia will also add virtual printers, allowing you to save print-outs to your Mac and send to apps.... Read more
Google Drive 1.24 - File backup and shar...
Google Drive is a place where you can create, share, collaborate, and keep all of your stuff. Whether you're working with a friend on a joint research project, planning a wedding with your fiancé, or... Read more
Chromium 45.0.2454.85 - Fast and stable...
Chromium is an open-source browser project that aims to build a safer, faster, and more stable way for all Internet users to experience the web. Version 45.0.2454.85: Note: Does not contain the "... Read more
OmniFocus 2.2.5 - GTD task manager with...
OmniFocus helps you manage your tasks the way that you want, freeing you to focus your attention on the things that matter to you most. Capturing tasks and ideas is always a keyboard shortcut away in... Read more
iFFmpeg 5.7.1 - Convert multimedia files...
iFFmpeg is a graphical front-end for FFmpeg, a command-line tool used to convert multimedia files between formats. The command line instructions can be very hard to master/understand, so iFFmpeg does... Read more
VOX 2.6 - Music player that supports man...
VOX is a beautiful music player that supports many filetypes. The beauty is in its simplicity, yet behind the minimal exterior lies a powerful music player with a ton of features and support for all... Read more
Box Sync 4.0.6567 - Online synchronizati...
Box Sync gives you a hard-drive in the Cloud for online storage. Note: You must first sign up to use Box. What if the files you need are on your laptop -- but you're on the road with your iPhone? No... Read more
Carbon Copy Cloner 4.1.4 - Easy-to-use b...
Carbon Copy Cloner backups are better than ordinary backups. Suppose the unthinkable happens while you're under deadline to finish a project: your Mac is unresponsive and all you hear is an ominous,... Read more
OmniGraffle Pro 6.3.1 - Create diagrams,...
OmniGraffle Pro helps you draw beautiful diagrams, family trees, flow charts, org charts, layouts, and (mathematically speaking) any other directed or non-directed graphs. We've had people use... Read more

Rock(s) Rider - HD Edition (Games)
Rock(s) Rider - HD Edition 1.0.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0.0 (iTunes) Description: *** PLEASE NOTE: Compatible with iPhone 4s, iPad 2, iPad mini, iPod touch (5th generation) or newer *** Do you... | Read more »
Rebuild 3: Gangs of Deadsville (Games)
Rebuild 3: Gangs of Deadsville 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: It's been a few years since the zombpocalypse turned the world's cities into graveyards and sent the few... | Read more »
Power Ping Pong (Games)
Power Ping Pong 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Do you wield your bat with zen-like focus or do your balls of fury give you a killer spin? Table tennis goes mobile with a... | Read more »
Z.O.N.A Project X (Games)
Z.O.N.A Project X 1.00 Device: iOS Universal Category: Games Price: $1.99, Version: 1.00 (iTunes) Description: Z.O.N.A Project X - shooter in the post-apocalyptic world. | Read more »
Trick Shot (Games)
Trick Shot 1.0.6 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0.6 (iTunes) Description: A game where all you have to do is throw a ball into a box, simple? Trick Shot is a minimalist physics puzzler with 90 levels... | Read more »
Goat Simulator MMO Simulator (Games)
Goat Simulator MMO Simulator 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: ** IMPORTANT - SUPPORTED DEVICESiPhone 4S, iPad 2, iPod Touch 5 or better.** Coffee Stain Studios brings next-gen... | Read more »
Worms™ 4 (Games)
Worms™ 4 1.02 Device: iOS Universal Category: Games Price: $4.99, Version: 1.02 (iTunes) Description: The latest instalment in the worldwide mega hit franchise! Coming soon to iPhone, iPad and iPod touch. When the guys and girls at... | Read more »
The Deer God (Games)
The Deer God 1.0 Device: iOS Universal Category: Games Price: $6.99, Version: 1.0 (iTunes) Description: 30% off launch sale!!! “It can be a struggle, but it's all worth it when you're shooting fire out your antlers.” Kotaku “The... | Read more »
AppSpy's Patreon campaign kicks off
Occasionally you'll see us use AppSpy's videos here on 148Apps to support an article we've written. That's because we're part of Steel Media, and AppSpy is Steel's video arm, so we're all part of one happy family. [Read more] | Read more »
We're Sorry to Report that Moonrise...
Moonrise is a very promising-looking, Pokemon-esque monster collecting and battling game that we were really looking forward to reviewing, but unfortunately it looks like that's never going to happen. [Read more] | Read more »

Price Scanner via

Will You Buy An iPad Pro? – The ‘Book Mystiqu...
It looks like we may not have to wait much longer to see what finally materializes as a new, larger-panel iPad (Pro/Plus?) Usually reliable Apple product prognosticator KGI Securities analyst Ming-... Read more
eFileCabinet Announces SMB Document Managemen...
Electronic document management (EDM) eFileCabinet, Inc., a hosted solutions provider for small to medium businesses, has announced that its SecureDrawer and eFileCabinet Online services will be... Read more
WaterField Designs Unveils American-Made, All...
San Francisco’s WaterField Designs today unveiled their all-leather Cozmo 2.0 — an elegant attach laptop bag with carefully-designed features to suit any business environment. The Cozmo 2.0 is... Read more
Apple’s 2015 Back to School promotion: Free B...
Purchase a new Mac or iPad at The Apple Store for Education and take up to $300 off MSRP. All teachers, students, and staff of any educational institution qualify for the discount. Shipping is free,... Read more
128GB MacBook Airs on sale for $100 off MSRP,...
B&H Photo has 11″ & 13″ MacBook Airs with 128GB SSDs on sale for $100 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 11″ 1.6GHz/128GB MacBook Air: $799.99, $100 off MSRP... Read more
13-inch 2.5GHz MacBook Pro (refurbished) avai...
The Apple Store has Apple Certified Refurbished 13″ 2.5GHz MacBook Pros available for $829, or $270 off the cost of new models. Apple’s one-year warranty is standard, and shipping is free: - 13″ 2.... Read more
27-inch 3.2GHz iMac on sale for $1679, save $...
B&H Photo has the 27″ 3.2GHz iMac on sale for $1679.99 including free shipping plus NY sales tax only. Their price is $120 off MSRP. Read more
Apple and Cisco Partner to Deliver Fast-Lane...
Apple and Cisco have announced a partnership to create a “fast lane” for iOS business users by optimizing Cisco networks for iOS devices and apps. The alliance integrates iPhone with Cisco enterprise... Read more
Apple offering refurbished 2015 13-inch Retin...
The Apple Store is offering Apple Certified Refurbished 2015 13″ Retina MacBook Pros for up to $270 (15%) off the cost of new models. An Apple one-year warranty is included with each model, and... Read more
Apple refurbished 2015 MacBook Airs available...
The Apple Store has Apple Certified Refurbished 2015 11″ and 13″ MacBook Airs (the latest models), available for up to $180 off the cost of new models. An Apple one-year warranty is included with... Read more

Jobs Board

*Apple* Desktop Analyst - KDS Staffing (Unit...
…field and consistent professional recruiting achievement. Job Description: Title: Apple Desktop AnalystPosition Type: Full-time PermanentLocation: White Plains, NYHot Read more
Simply Mac *Apple* Specialist- Repair Techn...
Simply Mac is the greatest premier retailer of Apple products expertise in North America. We're looking for dedicated individuals to provide personalized service and Read more
Simply Mac *Apple* Specialist- Service Repa...
Simply Mac is the greatest premier retailer of Apple products expertise in North America. We're looking for dedicated individuals to provide personalized service and Read more
*Apple* Desktop Analyst - KDS Staffing (Unit...
…field and consistent professional recruiting achievement. Job Description: Title: Apple Desktop AnalystPosition Type: Full-time PermanentLocation: White Plains, NYHot Read more
Simply Mac- *Apple* Specialist- Store Manag...
Simply Mac is the largest premier retailer for Apple products and solutions. We're looking for dedicated individuals with a passion to simplify and enhance the Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.