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File Handling in C++

File In a computer system files are used to store the necessary information / data stored. There are mainly two types of files:

Text file
Binary file

Text file. It stores information/data in ASCII characters. In text files, each line of text is terminated with a special character known as EOL (End of Line) character.

Binary file. It contains the data/information in the same format as it is held in memory. In binary files, no delimiters or EOF are used for a line for terminate the line

Classes for file stream operation

By using stream classes we can perform different operation such as read a file or write a file. There are some stream classes:

ofstream: This stream class is used to write on files
ifstream: This stream class is used to read from files
fstream: This stream class is used to both read and write from/to files.

Modes of file

Mode	Description
ios::in	open file for reading only
ios::out	open file for writing only
ios::binary	Open file in a binary mode.
ios::ate	Set the initial position at the end of the file. If the value of flag is not set to any value, then the by default initial position is the beginning of the file.
ios::app	All output operations are performed at the end of the file.
ios::trunc	If the file opened for output operations,then its previous content is deleted and replaced by the new one.

Opening a file:There are two ways for open a file:-

OPENING FILE USING CONSTRUCTOR

ofstream fout(“file1”);    //open a file “file1” for output only
ifstream fin(“data”);  //open a file “data” for input only

1 2	ofstream fout(“file1”); //open a file “file1” for output only ifstream fin(“data”); //open a file “data” for input only

OPENING FILE USING open()

Stream-object.open(“filename”, mode)
      ofstream ofile;
      ofile.open(“data1”);  	// open a file “data1” for write only
      
      ifstream ifile;
      ifile.open(“data2”);		// open a file “data2” for read only

Stream-object.open(“filename”, mode)

ofstream ofile;

ofile.open(“data1”); // open a file “data1” for write only

ifstream ifile;

ifile.open(“data2”); // open a file “data2” for read only

Example: Write a program to open a file using constructor & write a character in a file using write() function

int main() {
    ofstream f("E:\x.txt", ios::out); // open a file “x.txt” in a write mode
    char a;
    cout << "enter a character = ";
    cin >> a;
    f.write((char * ) & a, sizeof(a)); // write a character in file “x.txt”
    f.close(); // close a file
    return 0;
}

int main() {

ofstream f("E:\x.txt", ios::out); // open a file “x.txt” in a write mode

char a;

cout << "enter a character = ";

cin >> a;

f.write((char * ) & a, sizeof(a)); // write a character in file “x.txt”

f.close(); // close a file

return 0;

}

Output

enter a character=   x (Entered in console)


File x.txt
x

enter a character= x (Entered in console)

File x.txt

Note: In the above program, we are opening a file x.txt which is exists in an E drive with the help of ofstream class object (f).

After that we will enter character (x) in a console and and write the entered character in a file using wrire() function. Then we will close a file by using close () function.

Use of read() and write() function

“read () and write()” functions are used to performs the reading and writing operation in a file in a binary format.

The format of read() and write() function are as follows:

read( (char*)&p , sizeof(p) );

write( (char*)&p , sizeof(p) );

These function receives two argument. The first argument is the address of the variable P and the second argument is the size of variable P in byte.

Example: Write a program to open a file using open () function & write a character in a file using write () function.

int main() {
    ofstream f;
    char a;
    f.open("E: \x.txt", ios::app); // open file ”x.txt” from E drive
    cout << "enter a character=";
    cin >> a;
    f.write((char * ) & a, sizeof(a)); // write a character in file “x.txt”
    f.close(); // close a file
}

int main() {

ofstream f;

char a;

f.open("E: \x.txt", ios::app); // open file ”x.txt” from E drive

cout << "enter a character=";

cin >> a;

f.write((char * ) & a, sizeof(a)); // write a character in file “x.txt”

f.close(); // close a file

}

Output

enter a character=   x (Entered in console)


File x.txt
x

enter a character= x (Entered in console)

File x.txt

Note: In the above program, we are opening a file x.txt which is exists in an E drive with the help of ofstream class object (f).

After that we will enter character (x) in a console and write the entered character in a file using wrire() function.

Then we will close a file by using close () function.

Example: Write a program read a character in a file using read () function.

int main() {
    ifstream f;
    char a;
    f.open(“E: \x.txt”, ios:: in ); // open file ”x.txt” from E drive 
    f.read((char * ) & a, sizeof(a)); // read a character from file “x.txt”	
    cout << ”character = ” << a; // write a char in a console 
}

int main() {

ifstream f;

char a;

f.open(“E: \x.txt”, ios:: in ); // open file ”x.txt” from E drive

f.read((char * ) & a, sizeof(a)); // read a character from file “x.txt”

cout << ”character = ” << a; // write a char in a console

}

Output

character=   a (console)


File x.txt
ascdef

character= a (console)

File x.txt

ascdef

Note: In the above program, we are opening a file x.txt which is exist in a E drive.

After that we will read a character (a) from a file “x.txt” and write that character in a console.

Example: Write a program write and read a character in a file using read () & write () function. Use ifstream and ofstream class.

int main() {
    ofstream f;
    char a;
    f.open("E: \x.txt", ios::app); // open file ”x.txt” from E drive in write mode 	
    cout << "enter a character";
    cin >> a; // enter a character by user        
    f.write((char * ) & a, sizeof(a)); // write a character in file “x.txt”     
    f.close(); //close a file x.txt                    			
    ifstream f1;
    f1.open("E: \x.txt", ios:: in ); // open file ”x.txt” from E drive        	
    f1.read((char * ) & a, sizeof(a)); // read a character from file “x.txt”
    cout << "character = " << a; // write a char in a console
}

int main() {

ofstream f;

char a;

f.open("E: \x.txt", ios::app); // open file ”x.txt” from E drive in write mode

cout << "enter a character";

cin >> a; // enter a character by user

f.write((char * ) & a, sizeof(a)); // write a character in file “x.txt”

f.close(); //close a file x.txt

ifstream f1;

f1.open("E: \x.txt", ios:: in ); // open file ”x.txt” from E drive

f1.read((char * ) & a, sizeof(a)); // read a character from file “x.txt”

cout << "character = " << a; // write a char in a console

}

Output

enter a character=   s 
character = s


File Contains(s.txt)
s

enter a character= s

character = s

File Contains(s.txt)

Note: In the above program, we are opening a file x.txt which is exists in a E drive with the help of ofstream class object (f).

After that we will enter character (s) in a console and write the entered character in a file using wrire() function.

Then we will close a file by using close () function.

Again we will open a x.txt file with the help of ifstream class object (f1) and read a character (s) from a file and write that character in a console.

Example: Write a program to write and read a character in a file using read () & write () function. Use fstream class.

int main() {
    fstream f;
    char a;
    f.open("E: \x.txt", ios::app); // open file ”x.txt” from E drive				
    cout << "Enter a character = ";
    cin >> a; // enter a character by user        			
    f.write((char * ) & a, sizeof(a)); // write a character in file “x.txt”     
    f.close(); //close a file x.txt    
    f.open("E: \x.txt", ios:: in ); // open file ”x.txt” from E drive       
    f.read((char * ) & a, sizeof(a)); // read a character from file “x.txt”
    cout << "Character = " << a; // write a char in a console 
    f.close(); //close a file x.txt

}

int main() {

fstream f;

char a;

f.open("E: \x.txt", ios::app); // open file ”x.txt” from E drive

cout << "Enter a character = ";

cin >> a; // enter a character by user

f.write((char * ) & a, sizeof(a)); // write a character in file “x.txt”

f.close(); //close a file x.txt

f.open("E: \x.txt", ios:: in ); // open file ”x.txt” from E drive

f.read((char * ) & a, sizeof(a)); // read a character from file “x.txt”

cout << "Character = " << a; // write a char in a console

f.close(); //close a file x.txt

}

Output

enter a character= 											s 											character =s

1	enter a character= s character =s

Example: Write a program to write a string in a file using write () function.

int main() {
    ofstream f;
    char a[50];
    f.open("E: \x.txt", ios::app); // open file ”x.txt” from E drive		
    cout << "Enter a string";
    cin >> a; // string enter by user
    f.write((char * ) & a, sizeof(a)); // write an entered string in file “x.txt”
    f.close(); //close a file x.txt  
}

int main() {

ofstream f;

char a[50];

f.open("E: \x.txt", ios::app); // open file ”x.txt” from E drive

cout << "Enter a string";

cin >> a; // string enter by user

f.write((char * ) & a, sizeof(a)); // write an entered string in file “x.txt”

f.close(); //close a file x.txt

}

Output

Enter a string=
monu 


File Contains(s.txt)
monu

Enter a string=

monu

File Contains(s.txt)

monu

Example: Write a program to read a string in a file using read() function.

int main() {
    ifstream f;
    char a[50];
    f.open("E: \x.txt", ios:: in ); // open file ”x.txt” from E drive   
    f.read((char * ) & a, sizeof(a)); // read a string from file “x.txt”
    cout << "string = " << a; // write a string in a console 					

}

int main() {

ifstream f;

char a[50];

f.open("E: \x.txt", ios:: in ); // open file ”x.txt” from E drive

f.read((char * ) & a, sizeof(a)); // read a string from file “x.txt”

cout << "string = " << a; // write a string in a console

}

Output

string=  this                    (console)


File Contains(s.txt)
this is my book

string= this (console)

File Contains(s.txt)

this is my book

Note: Assume in a file “x.txt”, ”this is my book” is written. Then read () function will read only first string (this) or first 50 character string.

Example: Write a program to write and read a integer data in a file using read() & write() function. use ifstream and ofstream class.

int main() {
    ofstream f;
    int a;
    f.open("E: \x.txt", ios::app); // open file ”x.txt” from E drive
    cout << "enter a integer data";
    cin >> a; // enter integer by user 
    f.write((char * ) & a, sizeof(a)); // write a integer in file “x.txt”     
    f.close(); //close a file x.txt                    			
    ifstream f1;
    f1.open("E: \x.txt", ios:: in ); // open file ”x.txt” from E drive        
    f1.read((char * ) & a, sizeof(a)); // read a integer data from file “x.txt”	
    cout << "integer = " << a; // write a integer in a console            			
}

int main() {

ofstream f;

int a;

f.open("E: \x.txt", ios::app); // open file ”x.txt” from E drive

cout << "enter a integer data";

cin >> a; // enter integer by user

f.write((char * ) & a, sizeof(a)); // write a integer in file “x.txt”

f.close(); //close a file x.txt

ifstream f1;

f1.open("E: \x.txt", ios:: in ); // open file ”x.txt” from E drive

f1.read((char * ) & a, sizeof(a)); // read a integer data from file “x.txt”

cout << "integer = " << a; // write a integer in a console

}

Output

enter a integer data =  5
integer = 5                    (console)


File Contains(s.txt)
5

enter a integer data = 5

integer = 5 (console)

File Contains(s.txt)

Example: Write a program to write in a file using ofstream object.

 int main() {
     ofstream f; // create an object ‘f ’of ofstream   
     f.open("E: \x.txt", ios::out); // open file ”x.txt” from E drive in write mode	
     f << "aaaa bbbb cccc"; // write a statement in file “x.txt”			
     f << "\n xxxx yyyy zzzz"; // write a statement in file “x.txt”
     f.close(); //close a file x.txt    	                		
 }

int main() {

ofstream f; // create an object ‘f ’of ofstream

f.open("E: \x.txt", ios::out); // open file ”x.txt” from E drive in write mode

f << "aaaa bbbb cccc"; // write a statement in file “x.txt”

f << "\n xxxx yyyy zzzz"; // write a statement in file “x.txt”

f.close(); //close a file x.txt

}

Output

File Contains(s.txt)
aaaa bbbb cccc 
xxxx yyyy zzzz

File Contains(s.txt)

aaaa bbbb cccc

xxxx yyyy zzzz

Example: Write a program to write and read in a file using ofstream & ifstream object.

int main() {
    char a[20];
    ofstream f; // create an object ‘f ’of ofstream 
    f.open("E: \x.txt", ios::out); // open file ”x.txt” from E drive				
    f << "aaaa bbbb cccc"; // write a statement in file “x.txt”
    f << "\n xxxx yyyy zzzz"; // write a statement in file “x.txt”	
    f.close(); //close a file x.txt    				
    ifstream f1; // create an object ‘f1 ’of ifstream
    f1.open(“E: \x.txt”, ios:: in ); // open file ”x.txt” from E drive     
    f1 >> a; // read a string from file
    cout << a; // write in a console				
}

int main() {

char a[20];

ofstream f; // create an object ‘f ’of ofstream

f.open("E: \x.txt", ios::out); // open file ”x.txt” from E drive

f << "aaaa bbbb cccc"; // write a statement in file “x.txt”

f << "\n xxxx yyyy zzzz"; // write a statement in file “x.txt”

f.close(); //close a file x.txt

ifstream f1; // create an object ‘f1 ’of ifstream

f1.open(“E: \x.txt”, ios:: in ); // open file ”x.txt” from E drive

f1 >> a; // read a string from file

cout << a; // write in a console

}

Output

aaaa                 (console)


File Contains(x.txt)
aaaa bbbb cccc
xxxx yyyy zzzz

aaaa (console)

File Contains(x.txt)

aaaa bbbb cccc

xxxx yyyy zzzz

Note: In the above program, statement (f1>>a) will read only string “aaaa” from a file. If we will again read string using ifstream object f1 then for example

f1>>a;			// read a string from file					                                            cout<<a;		// write in a console								                                             f1>>a;  			// read a string from file							        cout<<a;  		// write in a console

1	f1>>a; // read a string from file cout<<a; // write in a console f1>>a; // read a string from file cout<<a; // write in a console

Output

aaaabbbb

aaaabbbb

Find End Of File (EOF)

We can find the end of file by using the eof() function.

The eof() function returns the non-zero value when end of file is detected, otherwise eof() function returns zero.

Example: Write a program to write and read in a file & display the content of file. Use eof() function.

int main() {
    char a[20];
    ofstream f;
    f.open("E: \x.txt", ios::out); // open file ”x.txt” from E drive				
    f << "aaaa bbbb cccc"; // write a statement in file “x.txt”	
    f << "\n xxxx yyyy zzzz"; // write a statement in file “x.txt”	
    f.close(); //close a file x.txt    				
    ifstream f1;
    f1.open("E: \x.txt", ios:: in ); // open file ”x.txt” from E drive       
    while (f1.eof() == 0) //eof() return 0 if end not detected 		
    {
        f1 >> a; // read a string from file					
        cout << a; // write in a console		
    }
}

int main() {

char a[20];

ofstream f;

f.open("E: \x.txt", ios::out); // open file ”x.txt” from E drive

f << "aaaa bbbb cccc"; // write a statement in file “x.txt”

f << "\n xxxx yyyy zzzz"; // write a statement in file “x.txt”

f.close(); //close a file x.txt

ifstream f1;

f1.open("E: \x.txt", ios:: in ); // open file ”x.txt” from E drive

while (f1.eof() == 0) //eof() return 0 if end not detected

{

f1 >> a; // read a string from file

cout << a; // write in a console

}

Output

aaaabbbbccccxxxxyyyyzzzz                (console)


File Contains(x.txt)
aaaa bbbb cccc  xxxx yyyy zzzz

aaaabbbbccccxxxxyyyyzzzz (console)

File Contains(x.txt)

aaaa bbbb cccc xxxx yyyy zzzz

Note: In the above program, statement

while (f1.eof() == 0) //eof() return 0 if end not detected	
{
    f1 >> a; // read a string from file		
    cout << a; // write in a console
}

while (f1.eof() == 0) //eof() return 0 if end not detected

{

f1 >> a; // read a string from file

cout << a; // write in a console

}

Initially function eof() return zero and condition will be true.

Then we will read a data from a file and print it in a console.

When function eof() detect the end of file then it will return non-zero value and then condition will be false and while loops terminates.

FILE POINTERS AND THEIR MANIPULATION

In a C++ file pointer is used to point to the reading or writing locations within a stream. There are following member functions of file pointer

Function	Description
seekg()	moves pointer to a specified location in write mode
seekp()	moves pointer to a specified location in read mode
tellp()	gives current position of the pointer for write
tellg()	gives current position of the pointer for read

Use of tellg()and tellp() functions

tellg() – gives current position of the pointer for write

tellp() – gives current position of the pointer for read

Example: Write a program to show the use of tellg() & tellp() function.

Write a program to show the present position of input and output pointer using tellg() & tellp().

int main() {
    char a[20];
    int loc;
    ofstream f;
    f.open("E: \x.txt", ios::out); // open file ”x.txt” from E drive in write mode	
    loc = f.tellp(); //  provides present position of output file pointer (0)
    cout << "position of o / p pointer = " << loc; // present position is 0		
    f << "aaaa bbbb cccc"; // write a statement in file “x.txt”
    loc = f.tellp(); //  provides present position of output file pointer (14)	
    cout << "after writing position of o / p pointer = " << loc; // present position is 14	
    f.close(); //close a file x.txt    				
    ifstream f1;
    f1.open("E: \x.txt", ios:: in ); // open file ”x.txt” from E drive in read mode     
    loc = f.tellg(); //  provides present position of input file pointer (0) 
    cout << "position of i / p pointer = " << loc; // present position is 0	  
    while (f1.eof() == 0) {
        f1 >> a; // read a string from file
    }
    loc = f.tellg(); //  provides present position of input file pointer (14) 	
    cout << "after reading position of o / p pointer = "<< loc; // present position is 14	 
    f1.close();
}

int main() {

char a[20];

int loc;

ofstream f;

f.open("E: \x.txt", ios::out); // open file ”x.txt” from E drive in write mode

loc = f.tellp(); // provides present position of output file pointer (0)

cout << "position of o / p pointer = " << loc; // present position is 0

f << "aaaa bbbb cccc"; // write a statement in file “x.txt”

loc = f.tellp(); // provides present position of output file pointer (14)

cout << "after writing position of o / p pointer = " << loc; // present position is 14

f.close(); //close a file x.txt

ifstream f1;

f1.open("E: \x.txt", ios:: in ); // open file ”x.txt” from E drive in read mode

loc = f.tellg(); // provides present position of input file pointer (0)

cout << "position of i / p pointer = " << loc; // present position is 0

while (f1.eof() == 0) {

f1 >> a; // read a string from file

}

loc = f.tellg(); // provides present position of input file pointer (14)

cout << "after reading position of o / p pointer = "<< loc; // present position is 14

f1.close();

}

Output

position of o/p pointer= 0                                 after writing position of o/p pointer= 14                              position of i/p pointer=  0                                                after reading position of o/p pointer=14    
           (console)


File Contains(x.txt)
aaaa bbbb cccc

position of o/p pointer= 0 after writing position of o/p pointer= 14 position of i/p pointer= 0 after reading position of o/p pointer=14

(console)

File Contains(x.txt)

aaaa bbbb cccc

Use of seekg()and seekp() functions

Function	Description
seekg()	moves pointer to a specified location in write mode
seekp()	moves pointer to a specified location in read mode

seekg() and seekp() function have a two arguments. Their format is fellows:-

seekg( offset , pre_position );

seekp( offset , pre_position );

first argument specifies the number of bites the file pointer is to be shifted from the pre_position of the pointer.

The pre_position may have one of the following possible values:-

pre_position	Description
ios :: beg	Beginning of the file
ios :: cur	Current position of the file pointer
ios :: end	End of the file

File Pointer With Its Arguments in a seekg() function

Seek Option	Working
seekg(0,ios :: beg );	Go to the beginning of the file.
seekg(0,ios :: cur );	Rest at the current position.
seekg(0,ios :: end );	Go to the end of the file.
seekg(n,ios :: beg );	Shift file pointer to n+1 byte in the file.
seekg(n,ios :: cur );	Go front by n byte from current position.
seekg(-n,ios :: cur );	Go back by n byte from the present position.
seekg(-n,ios :: end );	Go back by n byte from the end of position.

Example: Write a program to enter text and again second time re-enter text from beginning position and replace the first word and display the content after 10 byte of the file pointer from the beginning of the file.

Write a program to show the use of seekp() and seekg() function.

int main() {
    char a[20];
    ofstream f;
    f.open("E: \x.txt", ios::out); // open file ”x.txt” from E drive in write mode	
    f << "aaaa bbbb cccc"; // write a statement in file “x.txt”		
    f.seekp(0, ios::beg); // Go to the beginning of the file.	
    f << "xxxx"; // write a statement in file “x.txt”
    f.close(); //close a file x.txt    				
    ifstream f1;
    f1.open("E: \x.txt", ios:: in ); // open file ”x.txt” from E drive      	
    f1.seekg(10, ios::beg); // Shift file pointer to 10 byte in the file	  	    
    while (f1.eof() == 0) {
        f1 >> a; // read a string from file
        cout << a; // write in a console
    }
    f1.close();
}

int main() {

char a[20];

ofstream f;

f.open("E: \x.txt", ios::out); // open file ”x.txt” from E drive in write mode

f << "aaaa bbbb cccc"; // write a statement in file “x.txt”

f.seekp(0, ios::beg); // Go to the beginning of the file.

f << "xxxx"; // write a statement in file “x.txt”

f.close(); //close a file x.txt

ifstream f1;

f1.open("E: \x.txt", ios:: in ); // open file ”x.txt” from E drive

f1.seekg(10, ios::beg); // Shift file pointer to 10 byte in the file

while (f1.eof() == 0) {

f1 >> a; // read a string from file

cout << a; // write in a console

}

f1.close();

}

Output

cccc             (console)


File Contains(x.txt)
xxxx bbbb cccc

cccc (console)

File Contains(x.txt)

xxxx bbbb cccc

Note: In the above program, first, we write statement “aaaa bbbb cccc” then we will shift the output file pointer by using seekp() function (f.seekp(0, ios :: beg);)at the beginning of the file and again write statement ”xxxx” in place of “aaaa”.

Now the new statement/new content of file is “xxxx bbbb cccc”.

During reading file first we move the input file pointer 10 byte in a forward direction by using seekg() function (f1.seekg(10, ios :: beg);) then we will read file till end of file.

Example: Write a program using seekg() to achive the following:

To move the pointer by 15 position.
To go backward by 20 byte from the end.
To go byte 50 in the file.

First code is

#include <iostream>

using namespace std;

int main() {
    ifstream f1;
    f1.open("E: \x.txt", ios:: in ); // open file ”x.txt” from E drive for read
    f1.seekg(15, ios::cur); // Shift file pointer to 15th byte in the file	  	       
    while (f1.eof() == 0) {
        f1 >> a; // read a string from file
        cout << a; // write in a console	
    }
    f1.close();
}

#include <iostream>

using namespace std;

int main() {

ifstream f1;

f1.open("E: \x.txt", ios:: in ); // open file ”x.txt” from E drive for read

f1.seekg(15, ios::cur); // Shift file pointer to 15th byte in the file

while (f1.eof() == 0) {

f1 >> a; // read a string from file

cout << a; // write in a console

}

f1.close();

}

Second code is

#include <iostream>

using namespace std;

int main() {
    ifstream f1;
    f1.open("E: \x.txt", ios:: in ); // open file ”x.txt” from E drive      	
    f1.seekg(-20, ios::end); // Shift file pointer back to 20 byte from end of file
    while (f1.eof() == 0) {
        f1 >> a; // read a string from file	
        cout << a; // write in a console
    }
    f1.close();
}

#include <iostream>

using namespace std;

int main() {

ifstream f1;

f1.open("E: \x.txt", ios:: in ); // open file ”x.txt” from E drive

f1.seekg(-20, ios::end); // Shift file pointer back to 20 byte from end of file

while (f1.eof() == 0) {

f1 >> a; // read a string from file

cout << a; // write in a console

}

f1.close();

}

Third is

#include <iostream>

using namespace std;

 int main() {
    ifstream f1;
    f1.open("E: \x.txt", ios:: in ); // open file ”x.txt” from E drive  
    f1.seekg(50, ios::bg); // Shift file pointer to 50 byte in the file	  	  
    while (f1.eof() == 0) {
        f1 >> a; // read a string from file	
        cout << a; // write in a console
    }
    f1.close();
}

#include <iostream>

using namespace std;

int main() {

ifstream f1;

f1.open("E: \x.txt", ios:: in ); // open file ”x.txt” from E drive

f1.seekg(50, ios::bg); // Shift file pointer to 50 byte in the file

while (f1.eof() == 0) {

f1 >> a; // read a string from file

cout << a; // write in a console

}

f1.close();

}

Example: Write a program to copy the content of one file into another file.

int main() {
    char a[20];
    ofstream f;
    f.open("E: \x.txt", ios::out); // open file ”x.txt” from E drive					
    f << "aaaa bbbb cccc"; // write a statement in file “x.txt”
    f.close(); //close a file x.txt    				
    ifstream f1;
    f1.open("E: \x.txt", ios:: in ); // open file ”x.txt” from E drive      		
    ofstream f2;
    f2.open("E: \xyz.txt", ios::out); //  open file ”xyz.txt” from E drive      	                	
    while (f1.eof() == 0) {
        f1 >> a; // read a string from file x.txt
        f2 << a; // write in a file xyz.txt	
    }
    f1.close();
}

int main() {

char a[20];

ofstream f;

f.open("E: \x.txt", ios::out); // open file ”x.txt” from E drive

f << "aaaa bbbb cccc"; // write a statement in file “x.txt”

f.close(); //close a file x.txt

ifstream f1;

f1.open("E: \x.txt", ios:: in ); // open file ”x.txt” from E drive

ofstream f2;

f2.open("E: \xyz.txt", ios::out); // open file ”xyz.txt” from E drive

while (f1.eof() == 0) {

f1 >> a; // read a string from file x.txt

f2 << a; // write in a file xyz.txt

}

f1.close();

}

Output

aaaa bbbb cccc            (file x.txt)


aaaa bbbb cccc            (file xyz.txt)

aaaa bbbb cccc (file x.txt)

aaaa bbbb cccc (file xyz.txt)

Use of put() and get() function

“get()” is a member function of the class fstream. This function reads the single character from a file.

“put()” function is a member of fstream class. The put() function write a single character in the file.

Example: Write a program to write and read the characters in a file using put() & get() function.

#include <iostream>

using namespace std;

int main() {
    char a;
    ofstream f;
    f.open("E: \x.txt", ios::out);
    cout << "enter character = ";
    cin >> a; // character entered by user in console
    f.put(a); //  read console & write a character in file “x.txt”		
    f.close(); //close a file x.txt    				
    ifstream f1;
    f1.open("E: \x.txt", ios:: in ); // open file ”x.txt” from E drive     	
    f1.get(a); //  read a single character from file 	 	
    cout << "character = " << a;
    f1.close();
}

#include <iostream>

using namespace std;

int main() {

char a;

ofstream f;

f.open("E: \x.txt", ios::out);

cout << "enter character = ";

cin >> a; // character entered by user in console

f.put(a); // read console & write a character in file “x.txt”

f.close(); //close a file x.txt

ifstream f1;

f1.open("E: \x.txt", ios:: in ); // open file ”x.txt” from E drive

f1.get(a); // read a single character from file

cout << "character = " << a;

f1.close();

}

Output

Enter character=  s               
character = s            (console)


s          (file x.txt)

Enter character= s

character = s (console)

s (file x.txt)

Example: Write a program to write and read five characters in a file using put() & get() function.

#include <iostream>

using namespace std;

int main() {
    char a;
    ofstream f;
    f.open("E: \x.txt", ios::out);
    cout << "enter character = ";
    for (int i = 1; i <= 5; i++) {
        cin >> a;
        f.put(a); // write a character in file “x.txt”	
    }
    f.close(); //close a file x.txt    				
    ifstream f1;
    f1.open("E: \x.txt", ios:: in ); // open file ”x.txt” from E drive 
    cout << "character = ";
    for (int i = 1; i <= 5; i++) {
        f1.get(a); //  read the character from file
        cout << a;
    }
    f1.close();
}

#include <iostream>

using namespace std;

int main() {

char a;

ofstream f;

f.open("E: \x.txt", ios::out);

cout << "enter character = ";

for (int i = 1; i <= 5; i++) {

cin >> a;

f.put(a); // write a character in file “x.txt”

}

f.close(); //close a file x.txt

ifstream f1;

f1.open("E: \x.txt", ios:: in ); // open file ”x.txt” from E drive

cout << "character = ";

for (int i = 1; i <= 5; i++) {

f1.get(a); // read the character from file

cout << a;

}

f1.close();

}

Output

enter character = x                                           y				                  z				                   q                        				  u  			                        
character = xyzqu        (console)


xyzqu           (file x.txt)

enter character = x y z q u

character = xyzqu (console)

xyzqu (file x.txt)

Use of fail() function

“fail()” stream state member function is used to check whether a file has been opened for input or output successfully or not.

It returns the non-zero value if an operation is unsuccessful(or file is not opened) and return zero when it is open.

#include <iostream>

using namespace std;

int main() {
    ofstream f;
    f.open("E: \x.txt", ios::out); // open file ”x.txt” from E drive for write	
    if (f.fail() == 0) //fail() return 0 when file is open
    {
        f << "aaaa bbbb cccc"; // write a statement in file “x.txt”
        f.close(); //close a file x.txt 	
    } else {
        cout << "file is not opened.";
    }

}

#include <iostream>

using namespace std;

int main() {

ofstream f;

f.open("E: \x.txt", ios::out); // open file ”x.txt” from E drive for write

if (f.fail() == 0) //fail() return 0 when file is open

{

f << "aaaa bbbb cccc"; // write a statement in file “x.txt”

f.close(); //close a file x.txt

} else {

cout << "file is not opened.";

}

Output

aaaa bbbb cccc        (file x.txt)

1	aaaa bbbb cccc (file x.txt)

Note: In the above program, fail() return 0 when file is open and condition will be true after that we can perform operation and return non-zero value when file is not open and condition will be false.

Exception Handling

In C++ programming, an exception is an abnormal condition that arises/occurs in a source code during run time.

Exception is a run time error.

Example:

#include <iostream>
using namespace std;

int main() {
    int a, b;
    a = 0;
    b = 100 / a; //Error, Arithmetic Error
    cout << "a & b = " << a << b;
}

#include <iostream>

using namespace std;

int main() {

int a, b;

a = 0;

b = 100 / a; //Error, Arithmetic Error

cout << "a & b = " << a << b;

}

Output

Error, Arithmetic Error

1	Error, Arithmetic Error

When we try to compile this program we will receive an error message because value of 100/a (100/0) is infinite and it can’t be possible to save and print infinite value.

Handle Exception in C++

In a C++ programming language whenever an exceptional condition is arises it can be handled by the three keywords: try, catch and throw.

The Keyword try: Any code or statement that we want to monitor for an exception must be put inside the try block.

Syntax for try block:

try {
    statement 1;
    statement2;
}

try {

statement 1;

statement2;

}

Example:

try {
    statement 1;
    statement2;
}

try {

statement 1;

statement2;

}

In an above statement we have written try block.

Inside the try block we have placed a code (b=100/a) in which exception may occur.

Value of “ a” can be any integer value there is no problem but if the value of variable “a” is zero then error will generate because 100/a (100/0) is infinite and it can’t be possible to save and print infinite value.

The Keyword throw: If the exception occurs within try block it is automatically thrown by system or it can be manually thrown by using “throw” keyword. Syntax for throw:

throw (excep);

when excep is throw catch statement associated with the try block is handle this exception.

The Keyword catch: When the exceptional condition is arises within the try block it is thrown by the keyword throw and catch by the catch statement associated with the try block.

Syntax for catch block:

 try {
     statement 1;
     statement2;
 } catch (argument) {
     statement3;
 }

try {

statement 1;

statement2;

} catch (argument) {

statement3;

}

Note: If there is no exception within the try block then catch block will never execute.

Example: Write a program to show exception.

#include <iostream>

using namespace std;

int main() {
    int a, b;
    a = 0;

    b = 100 / a; // error,  arithmetic error
    cout << "\n a & b =" << a << b;
}

#include <iostream>

using namespace std;

int main() {

int a, b;

a = 0;

b = 100 / a; // error, arithmetic error

cout << "\n a & b =" << a << b;

}

Output

 
compile time error, arithmetic error

Example: Write a program to throw an exception when a =0 otherwise perform division.

 #include <iostream>

 using namespace std;

 int main() {
     int a, b;
     cout << "Enter the value of a =";
     cin >> a;
     try {
         if (a == 0) // if a=0 then throw exception & catch by catch ststement 

         {
             throw a;
         }
         b = 100 / a;
         cout << "\n a & b =" << a << b;
     } catch (int i) {
         cout << "Exception occurs because value of a is =" << i;
     }
     cout << "\n Exit main";
 }

#include <iostream>

using namespace std;

int main() {

int a, b;

cout << "Enter the value of a =";

cin >> a;

try {

if (a == 0) // if a=0 then throw exception & catch by catch ststement

{

throw a;

}

b = 100 / a;

cout << "\n a & b =" << a << b;

} catch (int i) {

cout << "Exception occurs because value of a is =" << i;

}

cout << "\n Exit main";

}

Output

(if a =0 then)     									                      enter the value of a =
0		// enter by user   
exception occurs because value of a is = 0
 exit main	

(Second condition if a =5 then Output)  		                          					                    enter the value of a =
5
 a & b =520
exit main

(if a =0 then) enter the value of a =

0 // enter by user

exception occurs because value of a is = 0

exit main

(Second condition if a =5 then Output) enter the value of a =

a & b =520

exit main

Example: Write a program to throw an exception when a =1 otherwise perform subtraction of x and y.

#include <iostream>

using namespace std;

int main() {
    int x, y, a;
    cout << "Enter the value of a ,x & u =";
    cin >> a >> x >> y;

    try {
        if (a == 1) {
            throw a;
        }
        cout << "x-y =" << (x - y);
    } catch (int i) {
        cout << "Exception occurs because value of a is =" << i;
    }
    cout << "Exit main";
    return 0;
}

#include <iostream>

using namespace std;

int main() {

int x, y, a;

cout << "Enter the value of a ,x & u =";

cin >> a >> x >> y;

try {

if (a == 1) {

throw a;

}

cout << "x-y =" << (x - y);

} catch (int i) {

cout << "Exception occurs because value of a is =" << i;

}

cout << "Exit main";

return 0;

}

Output

( if a=0 )
enter the value of a ,x & u =
1
5
4
exception occurs because value of a is =1
 exit main

enter the value of a ,x & u =
2
5
4
x-y =1 
exit main

( if a=0 )

enter the value of a ,x & u =

exception occurs because value of a is =1

exit main

enter the value of a ,x & u =

x-y =1

exit main

Multiple Catch Block

In a C++ programming we can define multiple catch statement for a single try block. Syntax for multiple catch is:

try {
    statement 1;
    statement2;
} catch (argument) {
    statement3;
} catch (argument) {
    statement4;
} catch (argument) {
    statement5;
}

try {

statement 1;

statement2;

} catch (argument) {

statement3;

} catch (argument) {

statement4;

} catch (argument) {

statement5;

}

Example: Write a program to throw multiple exception and defined multiple catch statement.

#include <iostream>

using namespace std;

void num(int a) {
    try {
        if (a == 0) {
            throw 'x';
        } else {
            if (a > 0)
                throw a;
            else
                throw 2.2;
        }
    } catch (int c) {
        cout << "\n positive value=" << c;
    } catch (char i) {
        cout << "\n value =" << i;
    } catch (double d) {
        cout << "\n negative  value =" << d;
    }
}

int main() {
    num(0);
    num(4);
    num(-1);
}

#include <iostream>

using namespace std;

void num(int a) {

try {

if (a == 0) {

throw 'x';

} else {

if (a > 0)

throw a;

else

throw 2.2;

}

} catch (int c) {

cout << "\n positive value=" << c;

} catch (char i) {

cout << "\n value =" << i;

} catch (double d) {

cout << "\n negative value =" << d;

}

int main() {

num(0);

num(4);

num(-1);

}

Output

value =x
 positive value=4
 negative  value =2.2

value =x

positive value=4

negative value =2.2

Default catch()

In a C++ exception handling it is also possible to define single or default catch block for one or more exception of different types.

In such a situation, a single catch block can catch exception thrown by multiple throw statement.

Example: Write a program to throw multiple exception and defined multiple catch statement.

#include <iostream>

using namespace std;

void num(int a) {
    try {
        if (a == 0) {
            throw a;
        } else {
            if (a > 0)
                throw 'X';
            else
                throw 2.2;
        }
    } catch (...) { // default catch	
        cout << "\n exception";
    }
}
int main() {
    num(0);
    num(4);
    num(-1);
}

#include <iostream>

using namespace std;

void num(int a) {

try {

if (a == 0) {

throw a;

} else {

if (a > 0)

throw 'X';

else

throw 2.2;

}

} catch (...) { // default catch

cout << "\n exception";

}

int main() {

num(0);

num(4);

num(-1);

}

Output

 exception
 exception
 exception

exception

Template in C++

In C++ programming language, Template is used to declare a group of function or class in a generic manner.

Generic means that that can process all types of data.

By using template a single function can defined for a group of functions, it is called as a “function template”.

Similarly, when template is associated with classes are known as class template.

Advantage of function template: It avoid unnecessary repetition of source code.

Using template we can create a single function that can process any type of data .

It can accept data of any type such as int, float, long etc.

Syntax for declare class template:

template class < T > class name_of_class {}

1	template class < T > class name_of_class {}

“template” is a keywords.

“template class <t>” statement tells the compiler the following class declaration can use the template data type.

Here T is a variable of template type. It is used to define variable of template (generic) type.

Within the angle bracket <> we declare a variable of template.

We can declare one or more variable separated by comma.

“template” always be global and should not be local means template cannot be declared inside of function or class.

T k; Where , k is variable of type template.

Normal Template Function Declaration

Syntax for Template Function

template class < T > type function_name() { // code }

Example: Write a program to perform constructor overloading and pass different data type argument.

#include <iostream>

using namespace std;

class A {
    public:
        A(char c) //	 constructor with character argument
    {
        cout << " c = " << c;
    }
    A(int i) //	constructor with integer argument	
    {
        cout << "\n i = " << i;
    }
    A(double d) //	constructor with double argument
    {
        cout << "\n d = " << d;
    }
};

int main() {
    A x('a'); // pass character data type
    A y(20); // pass integer data type
    A z(20.55); // pass double data type
}

#include <iostream>

using namespace std;

class A {

public:

A(char c) // constructor with character argument

{

cout << " c = " << c;

}

A(int i) // constructor with integer argument

{

cout << "\n i = " << i;

}

A(double d) // constructor with double argument

{

cout << "\n d = " << d;

}

};

int main() {

A x('a'); // pass character data type

A y(20); // pass integer data type

A z(20.55); // pass double data type

}

Output

 c = a
 i = 20
 d = 20.55

c = a

i = 20

d = 20.55

In the above program we have created three overloaded constructor, first accept integer data as argument and second accepts float data as argument and third constructor accepts character data as argument.

This approach has following disadvantages

Re-defining the same function separately for each data type. It increases the requires more time.
Size of program is increased. Hence, occupies more memory.
If constructor/function contains bug, it should be correct in every constructor/function.

Example: Write a program to create constructor and pass different data type as argument using template.

 #include <iostream>

 using namespace std;

 template < class T >
     class xyz {
         public:
             xyz(T c) {
                 cout << " c = " << c << endl;
             }
     };
 int main() {
     xyz < char > x('a'); // pass character data type
     xyz < int > y(20); // pass integer data type
     xyz < double > z(20.55); // pass double data type
 }

#include <iostream>

using namespace std;

template < class T >

class xyz {

public:

xyz(T c) {

cout << " c = " << c << endl;

}

};

int main() {

xyz < char > x('a'); // pass character data type

xyz < int > y(20); // pass integer data type

xyz < double > z(20.55); // pass double data type

}

Output

 c = a
 c = 20
 c = 20.55

c = a

c = 20

c = 20.55

In the above program we have created a class “xyz” and one constructor it can accept all data type because, constructor contains the variable of template T.

Normal Template Function Declaration

Syntax for Template Function

 2
 4

template class < T > type function_name() { // code
}

Example: Write a program to define normal template function.

#include <iostream>

using namespace std;

template < class T >
    void show(T x) {
        cout << "x = " << x << endl;

    }
int main() {
    char c = 'A';
    int i = 10;
    double d = 20.33;

    show(c);
    show(i);
    show(d);
}

#include <iostream>

using namespace std;

template < class T >

void show(T x) {

cout << "x = " << x << endl;

}

int main() {

char c = 'A';

int i = 10;

double d = 20.33;

show(c);

show(i);

show(d);

}

Output

 x = A
x = 10
x = 20.33

x = A

x = 10

x = 20.33

Example: Write a program to find the square of different data type using template.

#include <iostream>

using namespace std;

template < class T >
    class sqr {
        public:
            sqr(T c) // constructor 
        {
            cout << " square = " << (c * c) << endl;
        }
    };
int main() {
    sqr < int > y(25); //create object y, call constructor & pass integer data type
    sqr < double > z(15.2); //create object y, call constructor &  pass double data type
}

#include <iostream>

using namespace std;

template < class T >

class sqr {

public:

sqr(T c) // constructor

{

cout << " square = " << (c * c) << endl;

}

};

int main() {

sqr < int > y(25); //create object y, call constructor & pass integer data type

sqr < double > z(15.2); //create object y, call constructor & pass double data type

}

Output

  square = 625
 square = 231.04

1 2	square = 625 square = 231.04

Class Template With More Parameter

In C++ programming, class template can contain one or more parameter of generic data type.

The argument is separated by comma with template declaration.

Syntax for class template with more than one parameter:

template < class T1, class T2 > class name_of_class { }

Example: Write a program to define a constructor with multiple template variables.

#include <iostream>

using namespace std;

template < class T1, class T2 >
    class xyz {
        public:
            xyz(T1 a, T2 b) {
                cout << " a = " << a << "  b = " << b << endl;
            }
    };
int main() {
    xyz < int, float > x(2, 2.5);
    xyz < int, char > y(20, 'A');
    xyz < float, int > z(3.12, 50);
}

#include <iostream>

using namespace std;

template < class T1, class T2 >

class xyz {

public:

xyz(T1 a, T2 b) {

cout << " a = " << a << " b = " << b << endl;

}

};

int main() {

xyz < int, float > x(2, 2.5);

xyz < int, char > y(20, 'A');

xyz < float, int > z(3.12, 50);

}

Output

 a = 2  b = 2.5
 a = 20  b = A
 a = 3.12  b = 50

a = 2 b = 2.5

a = 20 b = A

a = 3.12 b = 50

Example: Write a program to exchange the value of two variable. Use Template variable as function argument.

#include <iostream>

using namespace std;

template < class T >
    void swap(T * a, T * b) {
        T temp;
        temp = * a;
        * a = * b;
        * b = temp;
    }

int main() {
    int x = 5, y = 10;

    cout << "before swap x = " << x << " & y =" << y;
    swap( & x, & y);
    cout << "\n after  swap x = " << x << " & y =" << y;

    double i = 2.22, j = 3.33;

    cout << "\n before swap i = " << i << " & j =" << j;
    swap( & i, & j);
    cout << "\n after  swap i = " << i << " & j =" << j;
}

#include <iostream>

using namespace std;

template < class T >

void swap(T * a, T * b) {

T temp;

temp = * a;

* a = * b;

* b = temp;

}

int main() {

int x = 5, y = 10;

cout << "before swap x = " << x << " & y =" << y;

swap( & x, & y);

cout << "\n after swap x = " << x << " & y =" << y;

double i = 2.22, j = 3.33;

cout << "\n before swap i = " << i << " & j =" << j;

swap( & i, & j);

cout << "\n after swap i = " << i << " & j =" << j;

}

Output

 before swap x = 5 & y =10
 after  swap x = 10 & y =5
 before swap i = 2.22 & j =3.33
 after  swap i = 3.33 & j =2.22

before swap x = 5 & y =10

after swap x = 10 & y =5

before swap i = 2.22 & j =3.33

after swap i = 3.33 & j =2.22

Overloading of Template Function

In a C++ programming language, like a function & constructor we can also override the template.

If we create more than one function with same name and one function take template type data as a argument and another function takes primitive data type as a argument then it overrides the function which takes template data as an argument.

#include <iostream>

using namespace std;

template < class T >
    void show(T x) {
        cout << "\n Template variable = " << x;
    }

void show(int i) {
    cout << "\n Integer variable = " << i;
}

int main() {
    show('A');
    show(10);
    show(50.55);
}

#include <iostream>

using namespace std;

template < class T >

void show(T x) {

cout << "\n Template variable = " << x;

}

void show(int i) {

cout << "\n Integer variable = " << i;

}

int main() {

show('A');

show(10);

show(50.55);

}

Output

 Template variable = A
 Integer variable = 10
 Template variable = 50.55

Template variable = A

Integer variable = 10

Template variable = 50.55

In the above program we have created two function (show ()) with same name.

One function take template type data as a argument and another function takes integer data type as a argument then it overrides the function which takes template data as an argument.

Abstract Class in C++

In a C++ programming language , a class that contains at least one pure virtual function is called abstract class.

This pure virtual function is a function is declared within base class and defined by derived class.

Like a other class abstract class can also contains normal function.

We can not create object of an abstract class,Any attempt to so will result in an error, but we can create reference to an abstract class.

#include <iostream>

using namespace std;

class A { //abstract  base class
    public:
        virtual void show() = 0; // pure virtual function 
    void display() {
        cout << "\n Display in abstract class";
    }
};
class B: public A { //derived class
    public: void show() {
        cout << " Show  of derived class ";
    }

};
int main() {

    B b;
    b.show(); // call to B’s show()
    b.display(); // call to A'a display()
}

#include <iostream>

using namespace std;

class A { //abstract base class

public:

virtual void show() = 0; // pure virtual function

void display() {

cout << "\n Display in abstract class";

}

};

class B: public A { //derived class

public: void show() {

cout << " Show of derived class ";

}

};

int main() {

B b;

b.show(); // call to B’s show()

b.display(); // call to A'a display()

}

Output

 Show  of derived class 
 Display in abstract class

1 2	Show of derived class Display in abstract class

Description: In the above program, we have declared a pure virtual function “show()” in a base class A which is defined by derived class B.

Because class A contain a pure virtual function therefore class A is an abstract class.

Abstract class can also contain a normal member function (in this program member function is display() ).

Virtual Function in C++

In a C++ programming language, A virtual function is a member function that is declared and defined within a base class and redefined by a derived class even if the number and type of argument are matching.

Rules for Virtual Function:

A virtual function may be declared as friend for another class.
Constructor cannot be declared as virtual, but destructor can be declared as virtual.
Like other function virtual function can return a value.

Example: Write a program to declare virtual function and executes the same function defined in base & derived class.

Write a program to use pointer for both base and derived class and call the member function. Use virtual keyword.

Write a program to create a virtual function.

#include <iostream>

using namespace std;

class A { // base class	
    public: virtual void show() {
        cout << "\n Show  of base class ";
    }
    virtual void display() {
        cout << "\n Display of base class ";
    }
};
class B: public A { //derived class
    public: void show() {
        cout << "\n Show  of derived class ";
    }
    void display() {
        cout << "\n Display of derived  class ";
    }
};

int main() {
    A a;
    B b;
    A * p;

    p = & a; // point to A
    p -> show(); // access  A’s show()
    p -> display(); // access  A’s display()

    p = & b; // point to B				
    p -> show(); // access  B’s show()
    p -> display(); // access  B’s display()
    return 0;
}

#include <iostream>

using namespace std;

class A { // base class

public: virtual void show() {

cout << "\n Show of base class ";

}

virtual void display() {

cout << "\n Display of base class ";

}

};

class B: public A { //derived class

public: void show() {

cout << "\n Show of derived class ";

}

void display() {

cout << "\n Display of derived class ";

}

};

int main() {

A a;

B b;

A * p;

p = & a; // point to A

p -> show(); // access A’s show()

p -> display(); // access A’s display()

p = & b; // point to B

p -> show(); // access B’s show()

p -> display(); // access B’s display()

return 0;

}

Output

 Show  of base class 
 Display of base class 
 Show  of derived class 
 Display of derived  class

Show of base class

Display of base class

Show of derived class

Display of derived class

Note: In the above program ‘a ‘is an object of base class A and ‘b’ is an object of derived class B.

The pointer variable ‘p’ point to the base class. In the statement “p = &a;” the address of object ‘a’ is assigned to pointer ‘p’.

Then the pointer calls the member function of class A.

Similarly, in the statement “p = &b;” the address of object ‘b’ is assigned to pointer ‘p’.

Then the pointer calls the member function of class B.

Pure Virtual Function

In a C++ programming language, A pure virtual function is a function which is declared within base class and defined by derived class.

We can declare a pure virtual function by using “virtual” keyword.

Any normal function cannot be declared as pure function. Syntax for declaration of pure virtual function:

virtual type function _name(parameter list)= 0;

Example: virtual void show () =0;

Example: Write a program to create a pure virtual function.

#include <iostream>

using namespace std;

class A { // base class
    public:
        virtual void show() = 0; // pure virtual function 
};
class B: public A { //derived class
    public: void show() {
        cout << " Show  of derived class ";
    }
};
int main() {

    B b;
    b.show(); // call to B’s show()
}

#include <iostream>

using namespace std;

class A { // base class

public:

virtual void show() = 0; // pure virtual function

};

class B: public A { //derived class

public: void show() {

cout << " Show of derived class ";

}

};

int main() {

B b;

b.show(); // call to B’s show()

}

Output

 Show  of derived class

1	Show of derived class

Description: In the above program, we have declared a pure virtual function “show ()” in a base class A which is defined by derived class B.

Function Overriding in C++

In a C++ programming language, it the base and derived both class has a function with same name and same parameter then derived class overrides the base class definition.

Such function’s are called overridden function and this process is called function overriding.

#include <iostream>

using namespace std;
class A { // base class	
    public: void show() {
        cout << "Show  of base class ";

    }
};
class B: public A { //derived class 
    public: void show() {
        cout << "Show  of derived class ";
    }
};
int main() {
    B b;
    b.show(); // derived class show()	
}

#include <iostream>

using namespace std;

class A { // base class

public: void show() {

cout << "Show of base class ";

}

};

class B: public A { //derived class

public: void show() {

cout << "Show of derived class ";

}

};

int main() {

B b;

b.show(); // derived class show()

}

Output

Show  of derived class

1	Show of derived class

Note: In the above program, class A & B both has a function (show ()) with same name and same parameter list.

When we call a show () function of base class A then show () function of derived class overrides the show () function of base class.

Constructor and Destructor Calling in C++

In a C++ programming language constructor are called from base class to derived class and destructor are called reverse of constructor means from derived class to base class.

Example: Write a program to show the sequence of execution of constructor and destructor.

#include <iostream>

using namespace std;
class A1 {
    public: A1() //   constructor  	
    {
        cout << "Constructor A1" << endl;
    }

    ~A1() //   Destructor  
    {
        cout << "Destructor A1"<< endl;
    }
};

class A2: public A1 { // derived class A2   

    public: A2() //   constructor  	
    {
        cout << "Constructor A2"<< endl;
    }~A2() //   Destructor 
    {
        cout << "Destructor A2"<< endl;
    }
};
class A3: public A2 { // derived class A3  
    public: A3() //   constructor  				
    {
        cout << "Constructor A3" << endl;
    }~A3() //   Destructor  
    {
        cout << "Destructor A3"<< endl;
    }
};
int main() {
    A3 ob;
}

#include <iostream>

using namespace std;

class A1 {

public: A1() // constructor

{

cout << "Constructor A1" << endl;

}

~A1() // Destructor

{

cout << "Destructor A1"<< endl;

}

};

class A2: public A1 { // derived class A2

public: A2() // constructor

{

cout << "Constructor A2"<< endl;

}~A2() // Destructor

{

cout << "Destructor A2"<< endl;

}

};

class A3: public A2 { // derived class A3

public: A3() // constructor

{

cout << "Constructor A3" << endl;

}~A3() // Destructor

{

cout << "Destructor A3"<< endl;

}

};

int main() {

A3 ob;

}

Output

Constructor A1
Constructor A2
Constructor A3
Destructor A3
Destructor A2
Destructor A1

Constructor A1

Constructor A2

Constructor A3

Destructor A3

Destructor A2

Destructor A1

Virtual Base Class in C++

In a C++ programming language to overcome the ambiguity problem occurred due to multipath inheritance we use “virtual” keyword.

By using the “virtual” keyword we can declares the specified class virtual.

When a class declared as virtual, then the compiler takes necessary precaution to avoid the duplication of member variable.

We can make a class virtual if it is a base class and is used by more than one derived classes as their base class.

Example: Write a program to declare virtual base classes. Derive a class using two virtual base class.

#include <iostream>

using namespace std;
class A1 {
    protected: int a1;
};
class A2: public virtual A1 { // virtual declaration 
    protected: int a2;
};
class A3: public virtual A1 { // virtual declaration  
    protected: int a3;
};
class A4: public A2, A3 { // virtual declaration 
    protected: int a4;
    public:
    void getdata() {
        cout << "Enter values of a1, a2, a3, a4";
        cin >> a1 >> a2 >> a3 >> a4;
    }
    void showdata() {
        cout << "values of a1, a2, a3, a4 = ";
        cout << a1 << a2 << a3 << a4;
    }
};
int main() {
    A4 obj;
    obj.getdata();
    obj.showdata();
   return 0;
}

#include <iostream>

using namespace std;

class A1 {

protected: int a1;

};

class A2: public virtual A1 { // virtual declaration

protected: int a2;

};

class A3: public virtual A1 { // virtual declaration

protected: int a3;

};

class A4: public A2, A3 { // virtual declaration

protected: int a4;

public:

void getdata() {

cout << "Enter values of a1, a2, a3, a4";

cin >> a1 >> a2 >> a3 >> a4;

}

void showdata() {

cout << "values of a1, a2, a3, a4 = ";

cout << a1 << a2 << a3 << a4;

}

};

int main() {

A4 obj;

obj.getdata();

obj.showdata();

return 0;

}

Output

 Enter values of a1, a2, a3, a4	
								              10													 20													 30													 40 												
                values of a1, a2, a3, a4= 10 20 30 40

Enter values of a1, a2, a3, a4

10 20 30 40

values of a1, a2, a3, a4= 10 20 30 40

Inheritance and types of Inheritance in C++

Inheritance is a one of the most important feature of object oriented programming.

Inheritance allow an object of one class to acquire the properties of another object of another class.

It supports the reusability and support hierarchical classification.

The class which inherits the another class is called derived class and the class which inherited is called base class.

Syntax of creating a derived class:

class derived_class_name: access_specifier base_class_name {}

1	class derived_class_name: access_specifier base_class_name {}

Example:

 class B : public A	// public derivation								{										}

1	class B : public A // public derivation { }

In the above syntax, class A is a base class, class B is a derived class. Here class B is derived publicly.

Example:

class B : private A	// private derivation								{										}

1	class B : private A // private derivation { }

In the above syntax, class A is a base class, class B is a derived class.

Here class B is derived privately.

Example:

class B :  A	// by default private derivation								{										}

1	class B : A // by default private derivation { }

If no access specifier is given , by default derivation is private.

Public & Private Inheritance: In a C++ when a class derived and public access specifier is used.

All the public member of base class can be accessed directly in the derived class but when private access specifier is used, then even public member of base class can not access directly in derived class

Public Inheritance: When a public access specifier is used, the public member of the base class are the public member of the derived class.

Example:

#include <iostream>

using namespace std;
class A { //   Base class							
    public: int x;
};
class B: public A { //   Derived class 
    public: int y;void show() {
        x = 10;
        y = 20; // x is also public member of derived class B	
        cout << x << "  " << y;
    }
};
int main() {
    B obj;
    obj.show();
}

#include <iostream>

using namespace std;

class A { // Base class

public: int x;

};

class B: public A { // Derived class

public: int y;void show() {

x = 10;

y = 20; // x is also public member of derived class B

cout << x << " " << y;

}

};

int main() {

B obj;

obj.show();

}

Output

10 20

10 20

Description: In the above program, class B derives class A means class A is a base class, class B is a derived class.

During inheriting a class public access specifier is used therefore public member of base class A can directly access in derived class B.

In above program “x” is a public member of base class A but it can directly access in derived class B.

Private Inheritance: When a class derived and private access specifier is used, then an object of derived class has no permission to access even public member of base class directly in main() function.

In such case, the public member of base class can be accessed using public member function of the derived class.

Example : When a class derived and private access specifier is used, then an object of derived class has no permission to access even public member of base class directly in main() function.

#include <iostream>

using namespace std;

class A { //   Base class
    public: int x;
};

class B: private A { //   Derived class
    public: int y;
};
int main() {
    B obj;
    obj.x = 10; // error, x is not accessible here because x is a private member of derived class
    obj.y = 20;
    cout << obj.x; // error, x is not accessible here because x is a private member of derived class
    cout << obj.y;
}

#include <iostream>

using namespace std;

class A { // Base class

public: int x;

};

class B: private A { // Derived class

public: int y;

};

int main() {

B obj;

obj.x = 10; // error, x is not accessible here because x is a private member of derived class

obj.y = 20;

cout << obj.x; // error, x is not accessible here because x is a private member of derived class

cout << obj.y;

}

Output

 obj.x = 10; // error, x is not accessible here because x is a private member of derived class
 cout << obj.x; // error, x is not accessible here because x is a private member of derived class

1 2	obj.x = 10; // error, x is not accessible here because x is a private member of derived class cout << obj.x; // error, x is not accessible here because x is a private member of derived class

Solution of such problem is that the public member of base class can be accessed using public member function of the derived class.

#include <iostream>

using namespace std;

class A { //   Base class
    public: int x;
};

class B: private A { //   Derived class  
    public: int y;
    void show() {
        x = 10;
        y = 20; // x is private member of derived class & accessible here		
        cout << x << "  " << y;
    }
};

int main() {
    B obj;
    obj.show();
}

#include <iostream>

using namespace std;

class A { // Base class

public: int x;

};

class B: private A { // Derived class

public: int y;

void show() {

x = 10;

y = 20; // x is private member of derived class & accessible here

cout << x << " " << y;

}

};

int main() {

B obj;

obj.show();

}

Output

10  20

10 20

Derived class can not access private data of base class

In a C++ programming ,derived class can’t access private data of base class.

If we will try to do so we will get an error message.

Example: In the below program we are trying to access the private data of base class in a derived class.

#include <iostream>

using namespace std;

class A { //   Base class
    private: int x;
};

class B: public A { //   Derived class  
    public: int y;
    void show() {
        x = 10;
        y = 20; //error, x is private member of derived class		
        cout << x << "  " << y; //error, x is private member of derived class
    }
};

int main() {
    B obj;
    obj.show();
}

#include <iostream>

using namespace std;

class A { // Base class

private: int x;

};

class B: public A { // Derived class

public: int y;

void show() {

x = 10;

y = 20; //error, x is private member of derived class

cout << x << " " << y; //error, x is private member of derived class

}

};

int main() {

B obj;

obj.show();

}

Output

 error: ‘int A::x’ is private within this context
 cout << x << "  " << y; //error, x is private member of derived class

1 2	error: ‘int A::x’ is private within this context cout << x << " " << y; //error, x is private member of derived class

Protected access specifier with public derivation : when a protected access specifier is used, the protected member of the base class are the protected member of the derived class.

Protected access specifier : A protected access specifier is similar to the private only difference is that it has a access to their derived classes.

Example 1

#include <iostream>

using namespace std;

class A { //   Base class
    protected: int x;
};

class B: public A { //   Derived class
    public: void show() {
        x = 10; //x is accessible here because x is protected member of derived class	
        cout << x;
    }
};

int main() {
    B obj;
    obj.show();
}

#include <iostream>

using namespace std;

class A { // Base class

protected: int x;

};

class B: public A { // Derived class

public: void show() {

x = 10; //x is accessible here because x is protected member of derived class

cout << x;

}

};

int main() {

B obj;

obj.show();

}

Output

10

Example 2

#include <iostream>

using namespace std;

class A { //   Base class
    protected: int x;
};
class B: public A { //   Derived class  
    protected: int y;
};
int main() {
    B obj;
    obj.x = 10; // error, x is not accessible here because x is a protected member of derived class                       
    obj.y = 20; //error	
    cout << obj.x << " " << obj.y; //error
    return 0;
}

#include <iostream>

using namespace std;

class A { // Base class

protected: int x;

};

class B: public A { // Derived class

protected: int y;

};

int main() {

B obj;

obj.x = 10; // error, x is not accessible here because x is a protected member of derived class

obj.y = 20; //error

cout << obj.x << " " << obj.y; //error

return 0;

}

Output

error: ‘int A::x’ is protected within this context
    obj.x = 10; // error, x is not accessible here because x is a protected member of derived class

1 2	error: ‘int A::x’ is protected within this context obj.x = 10; // error, x is not accessible here because x is a protected member of derived class

Types of Inheritance

There are following types of inheritance supported by C++:

Single Inheritance
Multilevel Inheritance
Multiple Inheritance
Hierarchical Inheritance
Hybrid Inheritance
Multipath Inheritance

Single inheritance: When only one class derived a class and derived class is not used as a base class such type of inheritance are called Single inheritance.

Here, X is a base class, Y is a derived class. In a single inheritance there is only one base class and one derived class.

Multilevel Inheritance When a class derived from another derived class such type of inheritance is called multilevel inheritance.

Here X is s base class for Y, Y is a derived class from X and Y is also base class for Z. Z is a derived class from Y.

Multiple Inheritance : When a single class is derived from two or more then two class then such type of inheritance is called multiple inheritance.

X & Y are the base class for Z , Z is deriver class. Class Z is derived from Class X & Y.

Hierarchical Inheritance: When a two or more classes are derived from a single base class is known as hierarchical inheritance.

W is a only base class and X,Y & Z are derived class. X,Y & Z are the derived from W.

Hybrid Inheritance : The combination of two or more inheritance are called hybrid inheritance.

In this type two types of inheritance are use single inheritance and multilevel inheritance.

Single Inheritance: W is a base class, Z is a derived class. Single inheritance has only one base class and one derived class.

Multilevel Inheritance:X is s base class for Y, Y is a derived class from X and base class for Z. Z is a derived class from Y.

Multipath Inheritance : When a class derived from two or more classes that are derived from same base class such type of inheritance is known as multipath inheritance.

W is a base class and X & Y are derived class. The class X & Y are the derived from W.

Further Z is derived from X & Y. means X & Y is a base class for Z and Z is a derived class.

Here, ambiguity is generated. Hence, virtual keyword is used to avoid ambiguity.

Single Inheritance

Single inheritance: When only one class derived a class and derived class is not used as a base class such type of inheritance are called Single inheritance.

Here, X is a base class, Y is a derived class. In a single inheritance there is only one base class and one derived class.

Example: Write a program to create a base class student and derived class record to read student record such as name, roll number, age & height and display by using single inheritance.

#include <iostream>

using namespace std;

class student { // base class
    protected:
        char name[20];
    int rollno;
};
class record: public student { // derived class
    public: float height;
    int age;
    void getdata() {
        cout << " Enter Name, Roll number, Height & Age";
        cin >> name >> rollno >> height >> age;
    }
    void showdata() {
        cout << "Name= " << name << endl;
        cout << "Roll number =" << rollno << endl;
        cout << "Height=" << height << endl;
        cout << "Age =" << age << endl;
    }
};

int main() {
    record obj;
    obj.getdata();
    obj.showdata();
}

#include <iostream>

using namespace std;

class student { // base class

protected:

char name[20];

int rollno;

};

class record: public student { // derived class

public: float height;

int age;

void getdata() {

cout << " Enter Name, Roll number, Height & Age";

cin >> name >> rollno >> height >> age;

}

void showdata() {

cout << "Name= " << name << endl;

cout << "Roll number =" << rollno << endl;

cout << "Height=" << height << endl;

cout << "Age =" << age << endl;

}

};

int main() {

record obj;

obj.getdata();

obj.showdata();

}

Output

 Enter Name, Roll number, Height & Age 
Ram
2 
5.6
22

Name= Ram
Roll number =2
Height=5.6
Age =22

Enter Name, Roll number, Height & Age

Ram

5.6

Name= Ram

Roll number =2

Height=5.6

Age =22

Note: In the above program, we have created base class student and derived class record.

Student class holds the protected data member name & rollno(A protected data member is similar to the private only difference is that it has a access to their derived classes).

Class record is derived from student means that it inherits all properties of student class.

Multilevel Inheritance :When a class derived from another derived class such type of inheritance is called multilevel inheritance.

Here X is s base class for Y, Y is a derived class from X and Y is also base class for Z. Z is a derived class from Y.

Example: Write a program to read student record such as name, roll number & age and display by using the concept of multilevel inheritance, create classes A1, A2 & A3.

#include <iostream>

using namespace std;
class A1 { // base class		
  protected: char name[20];
};
class A2: public A1 { // base class for A3 & derives class from A1	
  protected: int rollno;
};
class A3: public A2 { // derived class from A2
  protected: int age;
  public:
  void getdata() {
    cout << "Enter name, roll number & age";
    cin >> name >> rollno >> age;
  }
  void showdata() {
    cout << "name = " << name << endl;
    cout << "roll number = " << rollno << endl;
    cout << "age = " << age << endl;
  }
};
int main() {
  A3 obj;
  obj.getdata();
  obj.showdata();
  return 0;
}

#include <iostream>

using namespace std;

class A1 { // base class

protected: char name[20];

};

class A2: public A1 { // base class for A3 & derives class from A1

protected: int rollno;

};

class A3: public A2 { // derived class from A2

protected: int age;

public:

void getdata() {

cout << "Enter name, roll number & age";

cin >> name >> rollno >> age;

}

void showdata() {

cout << "name = " << name << endl;

cout << "roll number = " << rollno << endl;

cout << "age = " << age << endl;

}

};

int main() {

A3 obj;

obj.getdata();

obj.showdata();

return 0;

}

Output

Enter name, roll number & age
name = Ram
roll number = 2
age = 23

Enter name, roll number & age

name = Ram

roll number = 2

age = 23

Multiple Inheritance : When a single class is derived from two or more then two class then such type of inheritance is called multiple inheritance

X & Y are the base class for Z , Z is deriver class. Class Z is derived from Class X & Y.

Example: Write a program to derive a class from multiple base classes.

#include <iostream>

using namespace std;
class A { // base class									
  public: int a;
};
class B { // base class	
  public: int b;
};
class C { // base class						
  public: int c;
};
class D: public A, public B, public C { // derived class D
  public: int d;void getdata() {
    cout << " Enter values of a, b, c, d ";
    cin >> a >> b >> c >> d;
  }
  void showdata() {
    cout << "Values of a, b, c, d = " << a <<" " << b<<" " << c<<"  "<< d;
  }
};
int main() {
  D obj;
  obj.getdata();
  obj.showdata();
  return 0;
}

#include <iostream>

using namespace std;

class A { // base class

public: int a;

};

class B { // base class

public: int b;

};

class C { // base class

public: int c;

};

class D: public A, public B, public C { // derived class D

public: int d;void getdata() {

cout << " Enter values of a, b, c, d ";

cin >> a >> b >> c >> d;

}

void showdata() {

cout << "Values of a, b, c, d = " << a <<" " << b<<" " << c<<" "<< d;

}

};

int main() {

D obj;

obj.getdata();

obj.showdata();

return 0;

}

Output

  Enter values of a, b, c, d
  10	// enter by user	
  20	// enter by user
  30	// enter by user
  40	// enter by user	 
  Values of a, b, c, d= 10  20  30  40

Enter values of a, b, c, d

10 // enter by user

20 // enter by user

30 // enter by user

40 // enter by user

Values of a, b, c, d= 10 20 30 40

Note: In this program, A, B & C are the base class and class D is derived class from A ,B & C .

Class D inherits the properties of class A, B & C.

Hierarchical Inheritance: When a two or more classes are derived from a single base class is known as hierarchical inheritance

W is a only base class and X,Y & Z are derived class. X,Y & Z are the derived from W.

Example: Write a program to show the hierarchical inheritance.

#include <iostream>

using namespace std;
class A { // base class A					
  public: int a;
};
class B: public A { // derived class	B from class A
  public: int b;
  void showB() {
    a = 10;
    b = 20;
    cout << "a + b = " << (a + b)<<endl;
  }
};
class C: public A { // derived class	C  from class A	
  public: int c;
  void showC() {
    a = 10;
    c = 30;
    cout << "a + c = " << (a + c)<<endl;
  }
};
class D: public A { // derived class	D  from class A	
  public: int d;
  void showD() {
    a = 10;
    d = 40;
    cout << "a + d = " << (a + d)<<endl;
  }
};
int main() {
  B ob1;
  C ob2;
  D ob3;
  ob1.showB();
  ob2.showC();
  ob3.showD();
  return 0;
}

#include <iostream>

using namespace std;

class A { // base class A

public: int a;

};

class B: public A { // derived class B from class A

public: int b;

void showB() {

a = 10;

b = 20;

cout << "a + b = " << (a + b)<<endl;

}

};

class C: public A { // derived class C from class A

public: int c;

void showC() {

a = 10;

c = 30;

cout << "a + c = " << (a + c)<<endl;

}

};

class D: public A { // derived class D from class A

public: int d;

void showD() {

a = 10;

d = 40;

cout << "a + d = " << (a + d)<<endl;

}

};

int main() {

B ob1;

C ob2;

D ob3;

ob1.showB();

ob2.showC();

ob3.showD();

return 0;

}

Output

a + b = 30
a + c = 40
a + d = 50

a + b = 30

a + c = 40

a + d = 50

Note: A is a only base class. B, C & D are the derived class from A. Class B,C & D all inherits the properties of class A.

Hybrid Inheritance : The combination of two or more inheritance are called hybrid inheritance.

In this type two types of inheritance are use single inheritance and multilevel inheritance.

Single Inheritance: W is a base class, Z is a derived class. Single inheritance has only one base class and one derived class.

Multilevel Inheritance: X is s base class for Y, Y is a derived class from X and base class for Z. Z is a derived class from Y.

Example: Write a program to show the hybrid inheritance.

Write a program to create a derived class from multiple base class.

Write a program to create hybrid inheritance and take data members such as name of the player, age, city and game name.

#include <iostream>

using namespace std;

class location { // base class  
  public: char city[20];
};
class player { // base class	
  public: char name[20];
};
class year: public player { //   derived class from player & base class for game  
  public: int age;
};
class game: public year, public location { //  derived class from player & location.
  public: char game_name[20];
  void getdata() {
    cout << "Enter name, age, city & game name";
    cin >> name >> age >> city >> game_name;
  }
  void showdata() {
    cout << "name = " << name << endl;
    cout << "age = " << age << endl;
    cout << "city = " << city << endl;
    cout << "game name = " << game_name << endl;
  }
};
int main() {
  game ob;
  ob.getdata();
  ob.showdata();
}

#include <iostream>

using namespace std;

class location { // base class

public: char city[20];

};

class player { // base class

public: char name[20];

};

class year: public player { // derived class from player & base class for game

public: int age;

};

class game: public year, public location { // derived class from player & location.

public: char game_name[20];

void getdata() {

cout << "Enter name, age, city & game name";

cin >> name >> age >> city >> game_name;

}

void showdata() {

cout << "name = " << name << endl;

cout << "age = " << age << endl;

cout << "city = " << city << endl;

cout << "game name = " << game_name << endl;

}

};

int main() {

game ob;

ob.getdata();

ob.showdata();

}

Output

Enter name, age, city & game name
name = Ram
age = 23
city = Bhopal
game name = Chess

Enter name, age, city & game name

name = Ram

age = 23

city = Bhopal

game name = Chess

Note: In this type two types of inheritance are used single inheritance and multilevel inheritance.

Single Inheritance: location is a base class, game is a derived class.

Single level inheritance has only one base class and one derived class.

Class game inherits the properties of class location.

Multilevel Inheritance: player is a base class for Year, Year is a derived class from player .

year is a base class for game. game is a derived class from Year. Class game inherits the properties of both class player & year.

Multipath Inheritance : When a class derived from two or more classes that are derived from same base class such type of inheritance is known as multipath inheritance.

W is a base class and X & Y are derived class. The class X & Y are the derived from W. Further Z is derived from X & Y.

Means X & Y is a base class for Z and Z is a derived class. Here, ambiguity is generated.

Hence, virtual keyword is used to avoid ambiguity.

Example:

class A1 {
  protected: int a1;
};
class A2: public A1 {
  protected: int a2;
};
class A3: public A1 {
  protected: int a3;
};
class A4: public A2, public A3 {
  protected: int a4;
};

class A1 {

protected: int a1;

};

class A2: public A1 {

protected: int a2;

};

class A3: public A1 {

protected: int a3;

};

class A4: public A2, public A3 {

protected: int a4;

};

In the above example, A1 is a base class. The class A2 & A3 are the derived from class A1. Both A2 and A3 can access the variables/data of class A1 .

Further A4 is derived from A2 & A3.

If we try to access variable a1 of class A1 from class A4, Here, ambiguity is generated & compiler shows error message.

Member is ambiguous : “A1:a1” and “A1:a1”

The derived class A4 has two sets of data member of class A1 through the middle base classes A2 and A3.

The A1 is inherited twice.

Hence, virtual keyword is used to avoid ambiguity.

Operator Overloding in C++

In a C++ language, operator overloading is one of the important feature of c++.

It is an example of polymorphism. Polymorphism means one function having many forms .

There are different operators we use in a traditional programming language the operator such as +,-,*,/ etc.

For example: +( plus ) operator is used to perform addition of two variables , we cant add two object with “+” operator.

In C++ to perform operation with object we redefine the definitions of various operators.

Operator overloading feature helps to use these operators( +,- etc. ) with the object and object can be used in a natural manner as the variables of basic data types.

Example: Write a program to perform the addition of two object and store the result in third object. Display the content of third object.

#include <iostream>

using namespace std;

class xyz {
    public: int x, y;
    xyz() //	zero argument constructor
    {}
    xyz(int a, int b) //	two argument constructor
    {
        x = a;
        y = b;
    }
    void show() {
        cout << " x= " << x << " y = " << y << endl;
    }
}; // end of class

int main() {
    xyz A(2, 3), B(3, 4), C; // create three object & constructor called	
    A.show();
    B.show();
    C.x = A.x + B.x;
    C.y = A.y + B.y;
    C.show();
}

#include <iostream>

using namespace std;

class xyz {

public: int x, y;

xyz() // zero argument constructor

{}

xyz(int a, int b) // two argument constructor

{

x = a;

y = b;

}

void show() {

cout << " x= " << x << " y = " << y << endl;

}

}; // end of class

int main() {

xyz A(2, 3), B(3, 4), C; // create three object & constructor called

A.show();

B.show();

C.x = A.x + B.x;

C.y = A.y + B.y;

C.show();

}

Output

 x= 2 y = 3
 x= 3 y = 4
 x= 5 y = 7

x= 2 y = 3

x= 3 y = 4

x= 5 y = 7

Example: Write a program to perform addition of two objects using “operator” keyword.

  #include <iostream>

  using namespace std;

  class xyz {
      public: int x, y;
      xyz() //	zero argument constructor
      {}
      xyz(int a, int b) //	two argument constructor
      {
          x = a;
          y = b;
      }
      xyz operator + (xyz O1) {
          xyz O2;
          O2.x = x + O1.x;
          O2.y = y + O1.y;
          return O2;
      }
      void show() {
          cout << " x= " << x << " y = " << y << endl;
      }
  }; // end of class

  int main() {
      xyz A(2, 3), B(3, 4), C; // create three object & constructor called

      A.show();
      B.show();

      C = A + B;
      C.show();
  }

#include <iostream>

using namespace std;

class xyz {

public: int x, y;

xyz() // zero argument constructor

{}

xyz(int a, int b) // two argument constructor

{

x = a;

y = b;

}

xyz operator + (xyz O1) {

xyz O2;

O2.x = x + O1.x;

O2.y = y + O1.y;

return O2;

}

void show() {

cout << " x= " << x << " y = " << y << endl;

}

}; // end of class

int main() {

xyz A(2, 3), B(3, 4), C; // create three object & constructor called

A.show();

B.show();

C = A + B;

C.show();

}

Output

 x= 2 y = 3
 x= 3 y = 4
 x= 7 y = 3

x= 2 y = 3

x= 3 y = 4

x= 7 y = 3

Description : In the above program, A, B, C are the object of class xyz.

When the statement C= A + B is execute, the compiler searches for definition of operator + .

The object A call the operator function and object B is passed as an argument.

The copy of object B is stored in temporary object O1. In the operator function member variable of object A can directly accessible.

Then we have created additional object “O2” which holds the sum of objects A & O1 (B).

The return type of operator function is same as that of its class. The function return object O2 and it is assigned to object C.

Overloading Binary Operator

In a C++ programming, overloading with single operator is called a binary operator overloading.

In C++, like a arithmetic operator binary operator can also be overloaded.

Binary operator are overloaded by using member function and friend function.

1 Binary operator overloading using member function: In a binary operator overloading using member function one argument is required.

This argument contains value of the object.

For example: If we perform the addition of two object o1 & o2, then the overloaded function can declared as:

operator + (xyz o) ;

Where, “xyz” is a class name and “o” is the object. To call operator function the statement is as follow:

o3 = o1 + o2;

Here, object o1 call the operator function and object o2 is passed as an argument & copy of object “o2” store in temporary object ”o”.

The following statement can also be rewrite as:

o3 = o1.operator + (o2);

Example. Write a program to overload + binary operator.

#include <iostream>

using namespace std;

class xyz {
    public: int x, y;
    void getdata() {
        x = 5;
        y = 3;
    }
    xyz operator + (xyz O1) {
        xyz O2;
        O2.x = x + O1.x;
        O2.y = y + O1.y;
        return O2;
    }

    void show() {
        cout << " x= " << x << " y = " << y << endl;
    }
}; // end of class
int main() {
    xyz A, B, C;

    A.getdata();
    B.getdata();

    A.show();
    B.show();

    C = A + B;
    C.show();
}

#include <iostream>

using namespace std;

class xyz {

public: int x, y;

void getdata() {

x = 5;

y = 3;

}

xyz operator + (xyz O1) {

xyz O2;

O2.x = x + O1.x;

O2.y = y + O1.y;

return O2;

}

void show() {

cout << " x= " << x << " y = " << y << endl;

}

}; // end of class

int main() {

xyz A, B, C;

A.getdata();

B.getdata();

A.show();

B.show();

C = A + B;

C.show();

}

Output

 x= 5 y = 3
 x= 5 y = 3
 x= 10 y = 6

x= 5 y = 3

x= 10 y = 6

Note: In the above program, A, B, C are the object of class xyz.

When the statement C= A + B is execute, the compiler searches for definition of operator + .

The object A call the operator function and object B is passed as an argument.

The copy of object B is stored in temporary object O1.

In the operator function member variable of object A can directly accessible .

Then we have created additional object “O2” which holds the sum of objects A & O1 (B).

The return type of operator function is same as that of its class.

The function return object O2 and it is assigned to object C.

2. Binary operator overloading using friend function: In a C++ we can also overload binary operator by using friend function.

We can say friend function can be alternate of member function for overloading binary operator.

Both member & friend function gives the same result.

Friend function is generally useful when we perform an operation with operand of two different types.

For example consider the statement:

x = 3 + y ;

Where, x & y are the object of same type. 3 and ‘y’ will pass as an argument to the operator+() function and + operator will call operator+() function.

Example. Write a program to perform multiplication using an integer an object by using friend function.

#include <iostream>

using namespace std;

class xyz {
    public: int x, y;
    void getdata();
    void show();
    friend xyz operator * (int, xyz); // friend function declaration
}; // end of class

void xyz::getdata() {
    x = 5;
    y = 3;
}
void xyz::show() {
    cout << " x= " << x << " y =" << y << endl;
}

xyz operator * (int a, xyz obj) {
    xyz temp;
    temp.x = a * obj.x;
    temp.y = a * obj.y;
    return temp;
}
int main() {
    xyz A, B;

    A.getdata();
    A.show();

    B = 3 * A;
    B.show();
}

#include <iostream>

using namespace std;

class xyz {

public: int x, y;

void getdata();

void show();

friend xyz operator * (int, xyz); // friend function declaration

}; // end of class

void xyz::getdata() {

x = 5;

y = 3;

}

void xyz::show() {

cout << " x= " << x << " y =" << y << endl;

}

xyz operator * (int a, xyz obj) {

xyz temp;

temp.x = a * obj.x;

temp.y = a * obj.y;

return temp;

}

int main() {

xyz A, B;

A.getdata();

A.show();

B = 3 * A;

B.show();

}

Output

 x= 5 y =3
 x= 15 y =9

1 2	x= 5 y =3 x= 15 y =9

In the above program, A & B are the object of class xyz. Statement “ B = 3 * A ;” perform multiplication.

This statement contains both integer and class object.

As we known that left-hand operand is always used to call the function and right-hand operand passed as an argument.

But In this case left-hand operand is integer and cannot call the function.

The operator *( ) function is declared as friend .

When the Statement “ B = 3 * A ;” will execute it will call the “*” operator will call the operator*() function.