C++: The Complete Reference in .NET

Creation QR Code ISO/IEC18004 in .NET C++: The Complete Reference

brings the std namespace into visibility (ie, it puts std into the global namespace) After this statement has been compiled, there is no difference between working with an old-style header and a new-style one One other point: for the sake of compatibility, when a C++ program includes a C header, such as stdioh, its contents are put into the global namespace This allows a C++ compiler to compile C-subset programs

As explained, both namespaces and the new-style headers are fairly recent additions to the C++ language, added during standardization While all new C++ compilers support these features, older compilers may not When this is the case, your compiler will report one or more errors when it tries to compile the first two lines of the sample programs in this book If this is the case, there is an easy work-around: simply use an old-style header and delete the namespace statement That is, just replace

#include <iostream> using namespace std;

This change transforms a modern program into an old-style one Since the old-style header reads all of its contents into the global namespace, there is no need for a namespace statement One other point: for now and for the next few years, you will see many C++ programs that use the old-style headers and do not include a using statement Your C++ compiler will be able to compile them just fine However, for new programs, you should use the modern style because it is the only style of program that complies with the C++ Standard While old-style programs will continue to be supported for many years, they are technically noncompliant

This section introduces C++'s most important feature: the class In C++, to create an object, you first must define its general form by using the keyword class A class is similar syntactically to a structure Here is an example The following class defines a type called stack, which will be used to create a stack:

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// This creates the class stack class stack { int stck[SIZE]; int tos; public: void init(); void push(int i); int pop(); };

A class may contain private as well as public parts By default, all items defined in a class are private For example, the variables stck and tos are private This means that they cannot be accessed by any function that is not a member of the class This is one way that encapsulation is achieved access to certain items of data may be tightly controlled by keeping them private Although it is not shown in this example, you can also define private functions, which then may be called only by other members of the class To make parts of a class public (that is, accessible to other parts of your program), you must declare them after the public keyword All variables or functions defined after public can be accessed by all other functions in the program Essentially, the rest of your program accesses an object through its public functions Although you can have public variables, good practice dictates that you should try to limit their use Instead, you should make all data private and control access to it through public functions One other point: Notice that the public keyword is followed by a colon The functions init( ), push( ), and pop( ) are called member functions because they are part of the class stack The variables stck and tos are called member variables (or data members) Remember, an object forms a bond between code and data Only member functions have access to the private members of their class Thus, only init( ), push( ), and pop( ) may access stck and tos Once you have defined a class, you can create an object of that type by using the class name In essence, the class name becomes a new data type specifier For example, this creates an object called mystack of type stack:

stack mystack;

When you declare an object of a class, you are creating an instance of that class In this case, mystack is an instance of stack You may also create objects when the class is defined by putting their names after the closing curly brace, in exactly the same way as you would with a structure To review: In C++, class creates a new data type that may be used to create objects of that type Therefore, an object is an instance of a class in just the same way that some other variable is an instance of the int data type, for example Put differently, a class is a