C++ Programming Code Examples

In the C++ Programming Language, the #define directive allows the definition of macros within your source code. These macro definitions allow constant values to be declared for use throughout your code. Macro definitions are not variables and cannot be changed by your program code like variables. You generally use this syntax when creating constants that represent numbers, strings or expressions. The syntax for creating a constant using #define in the C++ is: #define token value • Using #define to create Macros Macros also follow the same structure as Symbolic Constants; however, Macros allow arguments to be included in the identifier: Unlike in functions, the argument here is enclosed in parenthesis in the identifier and does not have a type associated with it. Before compilation, the compiler will replace every instance of SQUARE_AREA(l) by ((l) * (l)), where l can be any expression. • Conditional Compilation There are several directives, which can be used to compile selective portions of your program's source code. This process is called conditional compilation. The conditional preprocessor construct is much like the 'if' selection structure. Consider the following preprocessor code:

The main purpose of C++ programming is to add object orientation to the C programming language and classes are the central feature of C++ that supports object-oriented programming and are often called user-defined types. A class is used to specify the form of an object and it combines data representation and methods for manipulating that data into one neat package. The data and functions within a class are called members of the class. When you define a class, you define a blueprint for a data type. This doesn't actually define any data, but it does define what the class name means, that is, what an object of the class will consist of and what operations can be performed on such an object. A class definition starts with the keyword class followed by the class name; and the class body, enclosed by a pair of curly braces. A class definition must be followed either by a semicolon or a list of declarations. For example, we defined the Box data type using the keyword class as follows: The keyword public determines the access attributes of the members of the class that follows it. A public member can be accessed from outside the class anywhere within the scope of the class object. You can also specify the members of a class as private or protected which we will discuss in a sub-section. A class provides the blueprints for objects, so basically an object is created from a class. We declare objects of a class with exactly the same sort of declaration that we declare variables of basic types. Following statements declare two objects of class Box: Both of the objects Box1 and Box2 will have their own copy of data members. The public data members of objects of a class can be accessed using the direct member access operator (.). It is important to note that private and protected members can not be accessed directly using direct member access operator (.). There are further interesting concepts related to C++ Classes and Objects which we will discuss in various sub-sections listed below: • Class Member Functions: A member function of a class is a function that has its definition or its prototype within the class definition like any other variable. • Class Access Modifiers: A class member can be defined as public, private or protected. By default members would be assumed as private. • Constructor & Destructor: A class constructor is a special function in a class that is called when a new object of the class is created. A destructor is also a special function which is called when created object is deleted. • Copy Constructor: The copy constructor is a constructor which creates an object by initializing it with an object of the same class, which has been created previously. • Friend Functions: A friend function is permitted full access to private and protected members of a class. • Inline Functions: With an inline function, the compiler tries to expand the code in the body of the function in place of a call to the function. • this Pointer: Every object has a special pointer this which points to the object itself. • Pointer to C++ Classes: A pointer to a class is done exactly the same way a pointer to a structure is. In fact a class is really just a structure with functions in it. • Static Members of a Class: Both data members and function members of a class can be declared as static.

Read block of data. Extracts n characters from the stream and stores them in the array pointed to by s. This function simply copies a block of data, without checking its contents nor appending a null character at the end. If the input sequence runs out of characters to extract (i.e., the end-of-file is reached) before n characters have been successfully read, the array pointed to by s contains all the characters read until that point, and both the eofbit and failbit flags are set for the stream. Internally, the function accesses the input sequence by first constructing a sentry object (with noskipws set to true). Then (if good), it extracts characters from its associated stream buffer object as if calling its member functions sbumpc or sgetc, and finally destroys the sentry object before returning. The number of characters successfully read and stored by this function can be accessed by calling member gcount. Pointer to an array where the extracted characters are stored. Number of characters to extract. streamsize is a signed integral type. Function returns the istream object (*this). Errors are signaled by modifying the internal state flags: • eofbit: The function stopped extracting characters because the input sequence has no more characters available (end-of-file reached). • failbit: Either the function could not extract n characters or the construction of sentry failed. • badbit: Error on stream (such as when this function catches an exception thrown by an internal operation). When set, the integrity of the stream may have been affected. Multiple flags may be set by a single operation. If the operation sets an internal state flag that was registered with member exceptions, the function throws an exception of member type failure. Modifies the elements in the array pointed to by s and the stream object. Concurrent access to the same stream object may cause data races, except for the standard stream object cin when this is synchronized with stdio (in this case, no data races are initiated, although no guarantees are given on the order in which extracted characters are attributed to threads). Basic guarantee: if an exception is thrown, the object is in a valid state. It throws an exception of member type failure if the resulting error state flag is not goodbit and member exceptions was set to throw for that state. Any exception thrown by an internal operation is caught and handled by the function, setting badbit. If badbit was set on the last call to exceptions, the function rethrows the caught exception.

In C++, constructor is a special method which is invoked automatically at the time of object creation. It is used to initialize the data members of new object generally. The constructor in C++ has the same name as class or structure. Constructors are special class functions which performs initialization of every object. The Compiler calls the Constructor whenever an object is created. Constructors initialize values to object members after storage is allocated to the object. Whereas, Destructor on the other hand is used to destroy the class object. • Default Constructor: A constructor which has no argument is known as default constructor. It is invoked at the time of creating object. • Parameterized Constructor: In C++, a constructor with parameters is known as a parameterized constructor. This is the preferred method to initialize member data. These are the constructors with parameter. Using this Constructor you can provide different values to data members of different objects, by passing the appropriate values as argument. • Copy Constructors: These are special type of Constructors which takes an object as argument, and is used to copy values of data members of one object into other object. The copy constructor is a constructor which creates an object by initializing it with an object of the same class, which has been created previously. The copy constructor is used to - • Initialize one object from another of the same type. • Copy an object to pass it as an argument to a function. • Copy an object to return it from a function. If a copy constructor is not defined in a class, the compiler itself defines one.If the class has pointer variables and has some dynamic memory allocations, then it is a must to have a copy constructor. The most common form of copy constructor is shown here.

The #ifndef directive of the C++ Programming Language helps in allowing the conditional compilation. The C++ Programming Language's preprocessor helps in determining only if the macro provided is not at all existed before including the specific subsequent code in the C++ compilation process. The #ifndef preprocessor only checks If the specific macro is not at all defined with the help of the #define directive. If the condition is TRUE then it will be helpful in executing the code otherwise the else code of the #ifndef will be compiled or executed only if present. The #ifndef works for the opposite condition of the #ifdef directive of the C Programming Language. The "MACRO" definition should not be defined for the specific preprocessor which is used to include the C Programming Source Code into the specific compiled application. The #ifndef must be ended with the #endif directive of the C Programming Language. If the #ifndef does not accept then else code statements will be printed which are actually used in including the specific which is defined. The #endif directive of the C Programming Language helps in closing the #ifndef directive of the C Programming Language. It is must and should end only with the #endif C Source code directive. The $ifndef directive usually checks/helps in seeing the specific identifier is currently not defined or not. The #ifndef preprocessor of the C Programming Language helps in allowing the conditional compilations. The preprocessor directive helps in determining whether the macro is existed or not before the subsequent code in the compilation process/ procedure. The #ifndef directive and #if !defined identifier are equivalent directives of the C Programming Language. The #ifndef directive helps in checking the opposite condition of the #ifdef directive of the C Programming Language. If the specified identifier is not even defined or definition is removed with the help of the #undef then the condition is TRUE for nonzero value or else the condition will be FALSE.

Write block of data. Inserts the first n characters of the array pointed by s into the stream. This function simply copies a block of data, without checking its contents: The array may contain null characters, which are also copied without stopping the copying process. Internally, the function accesses the output sequence by first constructing a sentry object. Then (if good), it inserts character into its associated stream buffer object as if calling its member function sputc until n characters have been written or until an insertion fails (in this case it sets the badbit flag). Finally, it destroys the sentry object before returning. Pointer to an array of at least n characters. Number of characters to insert. Integer value of type streamsize representing the size in characters of the block of data to write. streamsize is a signed integral type. Function returns the ostream object (*this). Errors are signaled by modifying the internal state flags: • eofbit: - • failbit: May be set if the construction of sentry failed. • badbit: Either an insertion on the stream failed, or some other error happened (such as when this function catches an exception thrown by an internal operation). When set, the integrity of the stream may have been affected. Multiple flags may be set by a single operation. If the operation sets an internal state flag that was registered with member exceptions, the function throws an exception of member type failure. Access up to n characters pointed by s. Modifies the stream object. Concurrent access to the same stream object may cause data races, except for the standard stream objects (cout, cerr, clog) when these are synchronized with stdio (in this case, no data races are initiated, although no guarantees are given on the order in which characters from multiple threads are inserted). Basic guarantee: if an exception is thrown, the object is in a valid state. It throws an exception of member type failure if the resulting error state flag is not goodbit and member exceptions was set to throw for that state. Any exception thrown by an internal operation is caught and handled by the function, setting badbit. If badbit was set on the last call to exceptions, the function rethrows the caught exception.

The C++ comments are statements that are not executed by the compiler. The comments in C++ programming can be used to provide explanation of the code, variable, method or class. If we write comments on our code, it will be easier for us to understand the code in the future. Also, it will be easier for your fellow developers to understand the code. By the help of comments, you can hide the program code also. There are two types of comments in C++: • Single Line comment • Multi Line comment The single line comment starts with // (double slash). C++ multi line comment is used to comment multiple lines of code. It is surrounded by slash and asterisk (/* ..... */). Comments shouldn't be the substitute for a way to explain poorly written code in English. We should always write well-structured and self-explanatory code. And, then use comments.