Thinking in C++ 2nd ed Volume 1 Revision 6

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So, although what we really do in object-oriented programming is create new data types, virtually all object-oriented programming languages use the “class” keyword. When you see the word “type” think “class” and vice versa 3 . Since a class describes a set of objects that have identical characteristics (data elements) and behaviors (functionality), a class is really a data type because a floating point number, for example, also has a set of characteristics and behaviors. The difference is that a programmer defines a class to fit a problem rather than being forced to use an existing data type that was designed to represent a unit of storage in a machine. You extend the programming language by adding new data types specific to your needs. The programming system welcomes the new classes and gives them all the care and type-checking that it gives to built-in types. The object-oriented approach is not limited to building simulations. Whether or not you agree that any program is a simulation of the system you’re designing, the use of OOP techniques can easily reduce a large set of problems to a simple solution. Once a class is established, you can make as many objects of that class as you like, and then manipulate those objects as if they are the elements that exist in the problem you are trying to solve. Indeed, one of the challenges of object-oriented programming is to create a one-to-one mapping between the elements in the problem space and objects in the solution space. But how do you get an object to do useful work for you There must be a way to make a request of that object so it will do something, such as complete a transaction, draw something on the screen or turn on a switch. And each object can satisfy only certain requests. The requests you can make of an object are defined by its interface, and the type is what determines the interface. A simple example might be a representation of a light bulb: 3 Some people make a distinction, stating that type determines the interface while class is a particular implementation of that interface. 44 Thinking in C++ www.BruceEckel.com
Type Name Interface Light +on() +off() +brighten() +dim() Light lt; lt.on(); The interface establishes what requests you can make for a particular object. However, there must be code somewhere to satisfy that request. This, along with the hidden data, comprises the implementation. From a procedural programming standpoint, it’s not that complicated. A type has a function associated with each possible request, and when you make a particular request to an object, that function is called. This process is usually summarized by saying that you “send a message” (make a request) to an object, and the object figures out what to do with that message (it executes code). Here, the name of the type/class is Light, the name of this particular Light object is lt, and the requests that you can make of a Light object are to turn it on, turn it off, make it brighter or make it dimmer. You create a Light object by simply declaring a name (lt lt) for that identifier. To send a message to the object, you state the name of the object and connect it to the message request with a period (dot). From the standpoint of the user of a pre-defined class, that’s pretty much all there is to programming with objects. The diagram shown above follows the format of the Unified Modeling Language (UML). Each class is represented by a box, with the type name in the top portion of the box, any data members that you care to describe in the middle portion of the box, and the member functions (the functions that belong to this object, which receive any messages you send to that object) in the bottom portion of the box. The ‘+’ signs before the member functions indicate they are public. Very often, only the name of the class and the public member functions are shown in UML design diagrams, and so the 1: Introduction to Objects 45
Page 1 and 2: Thinking in C++ 2 nd edition Volume
Page 3 and 4: TICA18: July 29, 1999. Rewrote Chap
Page 5 and 6: TICA7, August 14, 1998. Strings cha
Page 7 and 8: http://www.microsoft.com/typography
Page 9 and 10: In Bruce Eckel President, MindView
Page 11 and 12: MindView Ad Space
Page 13 and 14: Dedication To the scholar, the heal
Page 15 and 16: 2: Making & Using Objects 87 The pr
Page 17 and 18: Type-safe linkage............. 323
Page 19 and 20: protected ............. 618 protect
Page 21 and 22: Preface Like any human language, C+
Page 23 and 24: So the short answer is: what isn’
Page 25 and 26: end up losing some portion of the a
Page 27 and 28: Chapters C++ is a language in which
Page 29 and 30: Chapter 5: Hiding the Implementatio
Page 31 and 32: existing type. In this chapter you
Page 33 and 34: (and official mirror sites) where i
Page 35 and 36: note that the CD ROM is browser-bas
Page 37: Constantine, Lucy Lockwood, Tom Kef
Page 40 and 41: But computers are not so much machi
Page 42 and 43: the solution will run. There’s st
Page 46 and 47: middle portion is not shown. If you
Page 48 and 49: necessary to achieve the functional
Page 50 and 51: more specific types of trash are de
Page 52 and 53: Shape +draw() +erase() +move() +get
Page 54 and 55: Thermostat Controls Cooling System
Page 56 and 57: BirdController What happens when fl
Page 58 and 59: doStuff(c); What’s happening here
Page 60 and 61: The second approach is to create ob
Page 62 and 63: Analysis and design The object-orie
Page 64 and 65: It’s often proposed that you “b
Page 66 and 67: Phase 1: What are we making In the
Page 68 and 69: eveal itself in the fullness of tim
Page 70 and 71: getting into too much detail too ea
Page 72 and 73: 2. Object assembly. As you’re bui
Page 74 and 75: Phase 4: Iteration This is the poin
Page 76 and 77: will still function. You need not f
Page 78 and 79: You’re already on the learning cu
Page 80 and 81: large, complex program, there’s n
Page 82 and 83: first time, so it should not be mis
Page 84 and 85: Performance issues A common questio
Page 86 and 87: alternatives. Even if you eventuall
Page 88 and 89: By reading this chapter first, you
Page 90 and 91: takes several steps. The transition
Page 92 and 93: variable in another object module,
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point of definition the compiler al
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In a function declaration, you give
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cause the preprocessor to search fo
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until link time, one possibility is
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This book will use Standard C++ (an
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included the header file but all th
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"Hello, world!" And now, finally, t
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int main() { // Specifying formats
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Simple file manipulation Standard I
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This upward compatibility from C to
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iostream object. It’s that simple
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it’s much easier if you have each
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so if you have an array a and you w
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while(in >> word) is what gets the
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Exercises Solutions to selected exe
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If you’ve never seen C before, th
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} x = y = z; // ... It turns out th
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In cfunc( ), the first if that eval
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to a nonzero value). Other conditio
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while(guess != secret) { // Compoun
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curly brace ‘{’. This is in con
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switch(selector) { case integral-va
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using namespace std; void removeHat
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: C03:AutoIncrement.cpp // Shows us
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The first part of the program defin
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: C03:Specify.cpp // Demonstrates t
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All the variables, and even the fun
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from dog, bird is four bytes away f
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: C03:PassByValue.cpp #include usi
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pointers later, but this is arguabl
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All possible combinations of basic
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variable was defined. That is, a sc
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int main() { //.. { // Begin a new
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using namespace std; int globe; voi
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want a value to be extant throughou
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} int i; // The data definition voi
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The const was taken from C++ and in
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Operators and their use This sectio
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Introduction to preprocessor macros
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Bitwise not produces the opposite o
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An interesting bit pattern: unsigne
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x = a * -b; but the reader might ge
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Common pitfalls when using operator
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checking to catch errors. Once you
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(4) Implicit type conversions, norm
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Can't use xp as an X* at this point
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Keyword Meaning xor_eq ^= (bitwise
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The struct declaration must end wit
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int main() { Structure3 s1, s2; Str
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You can see how much more readable
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Once you perform an assignment, the
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for(int i = 0; i < 10; i++) cout
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Even though func1( ) and func2( ) d
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#include using namespace std; int
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++, which “adds one to the pointe
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int* ip = a; P(*ip); P(*++ip); P(*(
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in all upper case. A common flag na
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punctuation are concatenated into a
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Defining a function pointer To defi
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Using a function pointer Once you d
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Make: an essential tool for separat
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multiple rules. Many make programs
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target1.exe: target2.exe: If you ju
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Declare: Declare.o $(CPP) $(OFLAG)D
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lectures, exercises, and guided sol
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values in your instance and print t
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flag. You will need to consult your
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to switch from some language that y
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:~ A tag name like CStashTag is gen
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delete []s->storage; } } ///:~ init
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new unsigned char[newBytes]; The ge
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: C04:CLibTest.cpp //{L} CLib // Te
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Each separate C file is a translati
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of all their function names. So ini
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C library converted to C++ // Decla
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You can see that all the member fun
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: C04:CppLibTest.cpp //{L} CppLib /
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What's an object Now that you’ve
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Object details A question that come
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most of the time, except when struc
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included throughout the system, the
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This will yield a true result, and
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end up “turning off” namespaces
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} void Stack::initialize() { head =
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Read file and store lines in the St
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etween what the user of the structu
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16. Modify Stash to use a vector as
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5: Hiding the Implementation A typi
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The second reason for access contro
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Although func( ) can access any mem
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void Z::initialize() { j = 99; } vo
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private: Holder* h; int* p; public:
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second argument) for n bytes past t
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Any object belonging to this class
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The examples in this book, however,
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void initialize(); void push(void*
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Here’s a simple example demonstra
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u.cleanup(); } ///:~ The only thing
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9. Copy the implementation and test
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This not only provides a single uni
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Now, when an object is defined, voi
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The destructor is called automatica
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eginning of a scope. If a construct
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However, some confusion may result
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pointer “down” (a relative term
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} storage = b; // Point to new memo
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Stack with constructors & destructo
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ut is not responsible for cleaning
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Now if you decide to add another el
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zz[i].print(); } ///:~ Notice that
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Safety during coding is a big issue
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7: Function Overloading & Default A
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Although function overloading is a
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int f(); This works fine when the c
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~Stash(); int add(void* element); v
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Both constructors are exercised in
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Although the member functions civil
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(outside all functions and classes)
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Placeholder arguments Arguments in
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Mem::Mem(int sz) { mem = 0; size =
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int main() { MyString s("My test st
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Notice that a call to ensureMinSize
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7. Create a new version of the Stac
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This provides safety and control in
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const). Storage must be allocated b
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situations, const means “a piece
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has the option of doing constant fo
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const int* const x = &d; // (1) int
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Function arguments & return values
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Returning by value as a const becom
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temporary X. However, f7( ) takes i
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that attempting to modify the desti
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Error: const temporary created by f
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void print(); }; Fred::Fred(int sz)
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until Chapter 10: static. The stati
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The “enum hack” in old code In
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non-const member function. Thus, an
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cq.lastQuote(); // OK //! cq.quote(
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} int main() { const Z zz; zz.f();
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char Comm::read(int index) const {
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9. Write a const pointer to a doubl
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assign via a void* (without a cast)
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In C, one of the ways to preserve e
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granted. In the un-parenthesized ve
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mixed together, so a problem like t
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space than the code generated to do
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Here, the class user never has dire
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void setWidth(int w) { width = w; }
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updateLocal(); return local.tm_sec;
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if(storage != 0) delete []storage;
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The Stack class makes even better u
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Inlines & the compiler To understan
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class Forward { int i; public: Forw
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interface and thereby making the cl
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Because there are actually two stat
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} } exit(1); inline void assure(std
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C++ is complicated enough without a
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second function, without the need f
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10: Name Control Creating names is
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function. C and C++ allow you to cr
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int i; public: X(int ii = 0) : i(ii
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static Obj b inside f( ) and the st
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all you’ve done is change the vis
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Creating a namespace The creation o
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names in an unnamed namespace, you
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Integer a, b, c; Integer divide(Int
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} #endif // USINGDECLARATION_H ///:
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is not very safe. Global data can b
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ws.print(); } ///:~ Here, the quali
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static const X x3; static const X x
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A static member function cannot acc
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int main() { //! Egg x(1); // Error
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zeroing of the storage occupied by
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definition for the Initializer init
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constructor, so you can tell if the
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} static Dependency1 dep1; return d
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across the various translation unit
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that when you give the argument wit
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your namespace into that function s
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a Mirror object, which it assigns t
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Although references also exist in P
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2. Once a reference is initialized
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} ///:~ The call to f(1) produces a
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how does the compiler know how to p
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farther to provide storage for the
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output for bigfun( ), you can see i
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When the local object goes out of s
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} }; int HowMany2::objectCount = 0;
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cout.width(width); cout
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Temporary objects Line 15 begins th
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cout
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Here’s an example: //: C11:NoCopy
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combined with the object dereferenc
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fp = &Simple2::f; } ///:~ In the de
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underlying implementation without a
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the member functions const and prov
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21. Create a simple class without a
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The difference is that the argument
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} }; i += rv.i; return *this; int m
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operator++(Integer& a); // Postfix:
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} Byte operator!() const { cout
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an example of all the operators you
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friend int operator=(const Integer&
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if(&left == &right) {/* self-assign
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} #define TRYC(OP) \ out
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%= right.b; return *this; } Byte& o
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} Byte b3 = 92; b1 = b2 = b3; int m
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ack the object that was changed. Th
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left-hand side of an equal sign. Th
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class ObjContainer { vector a; publ
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#include #include "../require.h" u
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pointer,” although the example sh
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around and calls operator( ) for th
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eturn i[x]; } friend ostream& opera
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Operator &= |= %= >>=
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When you create an operator=, you m
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} ~Dog() { cout
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it. However, if your object require
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: p(dog), houseName(house) { cout
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Before you make any modifications (
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Automatic operator= creation Becaus
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In this case, automatic type conver
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Reflexivity One of the most conveni
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using namespace std; class Stringc
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: C12:TypeConversionFanout.cpp clas
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(the creator of the class) or the u
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16. Add an int data member to both
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13: Dynamic Object Creation Sometim
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Object creation When a C++ object i
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... sometime later: obj->destroy();
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with a call to free( )). Just as a
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Before a pointer to that block is r
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If you have a memory leak in your p
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The other change is the replacement
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can prevent a memory leak (more ele
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However, for the string pointers, i
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Now the array elements in q can be
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Another issue is heap fragmentation
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} free(m); class S { int i[100]; pu
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} for(int i = 0; i < psize; i++) if
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empty bracket syntax to indicate ar
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In both cases you’re handed the s
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When the program runs, it does not
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Notice that operator new only retur
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5. Repeat the above exercise, but a
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14: Inheritance & Composition One o
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int i; public: X() { i = 0; } void
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public: Y() { i = 0; } int change()
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The solution is simple: Call the co
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This makes built-in types act a lit
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#define CLASS(ID) class ID { \ publ
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properly reverse the order of the c
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in the new class. In the next chapt
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Name hiding comes into play here be
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~GameBoard() { cout
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ecause that function was not explic
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implementation hiding themselves, s
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} operator ifstream&() { return fil
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inherit privately, you’re “impl
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int read() const { return i; } void
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organic, evolutionary creature, rat
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your diagrams any way you find help
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Child object to a Parent& (if you c
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#include #include using namespace
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types inside the new type. Typicall
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class BusinessTraveler from Travele
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15: Polymorphism & Virtual Function
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quickly see the usefulness of this
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“narrow” that interface, but ne
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virtual void play(note) const { cou
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class Brass : public Wind { public:
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The keyword virtual tells the compi
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pointer (the VPTR) into the structu
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instrument pointer brass object VPT
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call word ptr [bx+4] Finally, the s
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from the previous assembly-language
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instrument virtual void play() virt
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cout
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may be a common piece of code that
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virtual string sit() const { return
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the examples you’ve seen here, an
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exists) and Dog, which no longer ex
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x = d2.f(); //! d2.f(s); // string
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int main() { Bird b; Cat c; Pet* p[
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Order of constructor calls The seco
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that is called last. This is anothe
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int main() { Base1* bp = new Derive
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The only distinction occurs when yo
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ely on portions of an object that h
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} Object* peek() const { return hea
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Creating containers that hold Objec
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using namespace std; class Shape {
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picture” of class relationships.
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12. Create a model of a greenhouse
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has no default constructor, so why
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16: Introduction to Templates Inher
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} int pop() { return stack[top > 0
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need an object, create it with new,
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object-based hierarchy with its con
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code. The container no longer holds
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In main( ), you can see how easy it
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people see software as a service, a
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} }; class Number { float f; public
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}* head; public: Stack() : head(0)
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changeable throughout the lifetime
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#ifndef AUTOCOUNTER_H #define AUTOC
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The destructor for CleanupCheck doe
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in the program, and you don’t nec
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int main() { Stack ac; // Ownership
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array, copying the old array to the
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of the underlying container) for an
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} friend ostream& operator
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} // Jump an iterator forward itera
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void push(T* dat) { head = new Link
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dereference operator performs the e
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To create the end sentinel: iterato
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} inflate(); storage[next++] = elem
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int main() { { // To force destruct
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class Square : public Shape { publi
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drawAll(p); cout
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that, to acquire a library from a t
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16. (Advanced) Modify PointerToMemb
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Although many of these issues have
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Begin and end comment tags A very i
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void func(int a) { you immediately
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The issue of where to put the openi
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Use of require( ) and assure( ) The
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also from the insights of friends i
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elationship where it doesn’t exis
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22. Don’t use private inheritance
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than global variables, although you
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the heap, the catcher must know to
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has enough information to deal with
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768 Thinking in C++ www.BruceEckel.
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C Thinking in C: Foundations for Ja
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Analysis & Design Extreme Programmi
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mathematical determinism and the il
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# compiler under dos: { all } # Obj
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C07:MemTest.cpp C09:Cpptime.cpp C12
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Index -, 177 --, 178 !, 177 !=, 172
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linking compiled C code with C++, 4
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declaration, 93, 245, 256 analyzing
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static member, 378, 440, 477 using
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Love, Tom, 777 lvalue, 170, 358 mac
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organization code, 260 code in head
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short, 145 side effect, 170, 178 si
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assembly-language code generated by
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