File Handling in C++

File Handling:

Header file used for file handling is fstream.h.

·        It is a process of storing data into files.

·        File handling transfers data between program and hard disk file.

·        C++ has its own function to access file data and store data into files.

Simple program:

void main()

{

            char *name; int roll_no;

            ofstream fout(“data”);

            fout<<”Rahul”;

            fout<<101;

            fout.close();

            ifstream fin(“data”);

            fin>>name;

            fin>>roll_no;

            cout<<roll_no<<name;

            fin.close();

}

File Modes:

File modes specify that, how file data will be read and write operation perform.

	Mode	Description
1.	ios::in	Open file for read only mode.
2.	ios::out	Open file for writing mode.
3.	ios::app	Append data to the end of file.
4.	ios::ate	Write data on the end of file and provide the facility of modifying existing contents.
5.	ios::binary	Create the binary file.
6.	ios::nocreate	Open fail if file does not exist.
7.	ios::noreplace	Open fail if file already exist.
8.	ios::trunc	Delete all the contents of the file if it exists. It will not create new file.

Note: The mode can combine two or more parameter using the bitwise OR (|).

Input and Output Functions for File handling:

·        Put and Get function:

                                i.            Put function:

The put function writes a single character to the associated stream/file.

For Ex:

file.put(c)

Writes a character c to the output buffer at the current put position and increases the put pointer to point the next character.

                              ii.            Get function:

The get function read a single character from the associated stream/file.

For Ex:

file.get(c)

Reads a character c from the current position and increment get pointer to the next character for next data get.

Sample program for file handling:

#include<iostream.h>

#include<conio.h>

#include<fstream.h>

void main()

{

            fstream file;

            file.open(“data.txt”,ios::in|ios::out);

            char c[4]={‘a’,’b’,’c’,’d’}, data;

            for(int i=0;c[i]!=NULL;i++)

            {

                        file.put(c[i]);

            }

            file.seekg(0);

            cout<<”\n Reading data from file\n”;

            while(file)

            {

                        file.get(data);

                        cout<<data;

            }

            file.close();

}

·        Write and read function:

Write and read functions are specially designed to input or output binary data in sequence.

file.read((char *)&v, sizeof(v));

file.write((char *)&v,sizeof(v));

file.read(memory_block,size);

file.write(memory_block,size);

Function for manipulating file pointer:

C++ provides some functions that relocate the file pointer and we can set any position inside the file.

                    i.            seekg():

Move get pointer to specific location.

                  ii.            seekp():

Move put pointer to specific location.

                iii.            tellg():

Give the current position of get pointer.

               iv.            tellp():

Give the current position of put pointer.

Reference Positions
0	ios::beg
1	ios::cur
2	ios::end

Examples:                                                                                          

file.tellp();

file.seekg(offset,reference position);

file.seekg(0);

Error handling in file operation:

Error that may occur –

                    i.            A file which we are trying to open for reading does not exist.

                  ii.            The file name used for a new file may already exist.

                iii.            We may use an invalid file name.

               iv.            There may not any space in the disk for storing more data.

Error handling functions for file handling –

        i.            eof():

Return true, if end of file (EOF) is detected while reading a file. Otherwise returns false.

      ii.            bad():

Return true, if an invalid operation has occurred, otherwise false.

    iii.            good():

Return true, if no error has occurred, otherwise return fail.

   iv.            fail():

Return true, when an input or output operation has failed.