Files Theory

 File handling

Stream:

Stream means flow of data.

Input stream means flow of data from file to program.

Output stream is the flow of data from program to file.

Stream Class Model:

§  ios: This is base class of stream class hierarchy. istream class and ostream class are inherited from this class.   

§  istream: This class is inherited from ios class. This class is useful for input stream. If we want to read data from file to the program this class is used.

§  ostream: This class is inherited from ios class. This class is useful for output stream. If we want to write data to file from the program ostream class is used.

§  iostream: This class is inherited from ostream class and istream class. It is work as a base class for fstream class.

§  fstream: This class is inherited from iostream class. This class is used to write and read from the file.

§  ifstream: This class is used to read data from the file.

§  istream_withassign: This class is inherited from istream class. Cin is an object of istream_withassign class.

§  ofstream: This class is used to write data to file.

§  ostream_withassign: This class is inherited from ostream class. Cout is an object of ostream_withassign class.

Text output

Text output is possible with two options. 1. Insertion operator 2. Put function

Insertion operator:  It is used to write data from program to file.

void main()

{

     char c=‘a’;

    ofstream of1(“test.dat”);

    of1<<c;

}         

Same way we can write data of integer, float or string type also.

  Put() function :  The put() function is member of the ostream class.

   Prototype of put()

 ostream & ostream :: put(char c)

The put function is called through an object of ostream ,or an object of any subclass of ostream class.

void main()

{

     char c=‘a’;

    ofstream of1(“test.dat”);

    of1.put(c);

}         

 

Text input : There are three options for text input

§  Extraction operator

§  get()

§  getline()

Extraction operator

It is used to get input from file to the program

It is overloaded in istream class.

void main()

{

    char c;

   ifstream if1(“test.dat”);

   if1>>c;

  cout<<c;

}

Extraction operator can work with int, float and string also.

get() function

§  The get function is available in istream class.

§  The get function read single byte from the file and stores in character variable.

§  It is member of istream class and can be invoked with istream class object or object of subclass of istream class object.

§  The prototype of istream class is:

istream & istream :: get(char &); 

Example of get()

void main()

{

    char c;

   ifstream if1(“test.dat”);

   if1.get(c);

  cout<<c;

}

 

getline() function

§  This function is used to read complete line from the file.

§  It is member of istream class.

§  The prototype is:

 istream & istream getline(char  * ,int , char=‘\n’)

The first parameter suggest, the string that has been read by the getline function

The second parameter is the number of character to be read by the getline function.

The third parameter is character that suggest, up to that character the string to be read. The default value of the third character is ‘\n’.

The getline() will read upto first occurrence from the second and third arguments.