C++1
OOP in C++
CONSTRUCTOR INITIALIZATION LISTS
- Generally every object we create will require some sort of initialization. C++
allows a constructor function to be included in a class declaration. A class’s constructor is called each time an object of that class is created.
- Thus, any initialization to be performed on an object can be done automatically by the constructor function. A constructor function has the following characteristics : –
- It should have the same name as that of the class.
- It should not have any return type even void however they can take arguments.
- onstructers can take default arguments
- Constructers can be dynamically initialized.
- Constructer function cannot be made virtual
- It should be always declared in the public section of the class.
Example: The following program makes use of a constructor.
#include <iostream.h >
#include <conio.h >
class number
{int a;
public:
number( ); //constructor
void show( );};
Public number( )
{cout<< “In constructor\n”;
a=100;}
void show( )
{cout << a;}
void main( )
{clrscr();
number ob; // automatic call to constructor
ob.show( );
getch();
}
Output of the Program
In constructor
100
- In this simple example the constructor is called when the object is created, and the constructor initializes the private variable a to 100 .For a global object, its constructor is called once, when the program first begins execution. For local objects, the constructor is called each time the declaration statement is executed.
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OOP in C++
For the students of FYBSc (IT), SYBSc (CS), SYBCA
THE 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. 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:
classname (const classname &obj){ // body of constructor}
Here, obj is a reference to an object that is being used to initialize another object.
#include<iostream>
classLine
{
public:
int getLength(void);
Line(int len ); // simple constructor
Line(constLine&obj); // copy constructor
~Line(); // destructor
private:
int*ptr;
};
// Member functions definitions including constructor
Line::Line(int len)
{
cout <<“Normal constructor allocating ptr”<< endl;
// allocate memory for the pointer;
ptr =newint;
*ptr = len;
}
Line::Line(constLine&obj)
{
cout <<“Copy constructor allocating ptr.”<< endl;
ptr =newint;
*ptr =*obj.ptr;// copy the value
}
Line::~Line(void)
{
cout <<“Freeing memory!”<< endl;
delete ptr;
}
intLine::getLength(void)
{
return*ptr;
}
void display(Line obj)
{
cout <<“Length of line : “<< obj.getLength()<<endl;
}
// Main function for the program
void main()
{ Line line(10);
display(line);}
When the above code is compiled and executed, it produces the following result:
Normal constructor allocating ptr
Copy constructor allocating ptr.
Length of line : 10
Freeing memory!
Freeing memory!
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OOP in C++
For the students of FYBSc (IT), SYBSc (CS), SYBCA
C++ Identifiers:
- A C++ identifier is a name used to identify a variable, function, class, module, or any other user-defined item. An identifier starts with a letter A to Z or a to z or an underscore (_) followed by zero or more letters, underscores, and digits (0 to 9).
- C++ does not allow punctuation characters such as @, $, and % within identifiers.
- C++ is a case-sensitive programming language. Thus, Manpower and manpower are two different identifiers in C++.
- Here are some examples of acceptable identifiers:
Name1 abc move_name a_123
Myname_50 num1 num2 temp retVal
C++ Keywords:
- The following list shows the reserved words in C++. These reserved words may not be used as constant or variable or any other identifier names.
else new this Auto enum operator throw Bool explicit
private true Break export protected try Case extern public typedef
Catch false register typeid Char float reinterpret_cast typename
Class for return union Const friend short unsigned const_cast goto signed using
continue If sizeof virtual Default inline Static void Delete int static_cast volatile
Do long Struct Double mutable Switch while dynamic_cast namespace Template
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