Data file handling

DataFileHandling
Prof. K. Adisesha

Learning Outcomes
 Introduction
 Stream in C++
 file stream operation
 Types of data Files
 Opening and Closing of Files
 File Modes
 Input and Output Operation file
 File pointers
2

Introduction
File Definition:
3

Introduction
File Definition:
 A file is a collection of related data stored in a particular
area on the disk.
 Programs can be designed to perform the read and write
operations on these files.
 In general a file is a sequence of bits, bytes, lines or
records whose meaning is defined by its user.
 C++ I/O occurs in streams, which are sequence of bytes.
 If bytes flows from device like a keyboard, a disk drive,
etc., to main memory, this is called input operation.
4

Stream in C++
Definition:
 A stream is sequence of bytes. In C++, a stream is a
general name given to flow of data.
 The three streams in C++ are as follows.
 Input Stream: The stream that supplies data to the
program is known as input stream.
 Output Stream: The stream that receives data from the
program is known as output stream.
 Error Stream: Error streams basically an output stream
used by the programs to the file or on the monitor to report
error messages.
5

File headers
fstream.h header file:
 The I / O system of C++ contains a set of classes that define
the file handling methods.
 These include:
 ifstream
 ofstream
 fstream
 These classes are derived from fstream base and from the
corresponding iostream.h.
 These classes, designed to manage the disk files, are declared
in fstream.h and therefore we must include this file in any
program that uses files.
6

file stream operation
Classes for file stream:
7

file stream operation
Classes for file stream operation:
8
Class Meanings
filebuf It sets the file buffer to read and write
fstreambase
It serves as a base class for the derived classes ifstream, ofstream
and fstream and contains open( ) and close( ) as member functions
ifstream
It supports input operations.
It contains open( ) with default input mode and inherits get( ),
getline( ), read( ), seekg( ) and tellg( ) functions from istream.
ofstream
It supports output operations.
It contains open( ) with default output mode and inherits put( ),
seekp( ), tellp( ) and write( ) functions from ostream
fstream
It supports simultaneous input and output operations.
It contains open( ) with default input mode and inherits all the
functions from istream and ostream classes through iostream

Types of Files
Types of data Files:
 Generally there are two types of files in C++:
 Text Files:
 A text file is a file that stores the information in ASCII
characters.
 Each line of text is terminated by a special character, known as
End of Line (EOL) or delimiter.
 Binary Files:
 A binary file is a file that contains information in the same
format as it is held in memory.
 In binary files, no delimiters are used for a line and no
translations occur here.
9

Files Operations
Opening Files:
 A file must first be opened before data can be read from it or
written to it.
 In C++ there are two ways to open a file with the file stream
object.
 Opening file using constructor.
 Opening file using open ( ) member function.
 The first method is preferred when a single file is used with a
stream.
 However for managing multiple files with the same stream, the
second method is preferred.
10

Opening Files
Opening file using constructor:
 In order to access a file, it has to be opened either in read, write
or append mode.
 In all the three file stream classes, a file can be opened by
passing a filename as the first parameter in the constructor
itself.
 The syntax for opening a file using constructor is:
 streamclass_name file_objectname (“filename”)
 Example:
 ofstream fout (“results.dat”);
 ifstream fin (“results.dat”);
11

Opening Files
Opening files using open( ):
 open( ) can be used to open multiple files that use the
same stream object.
 Syntax for opening a file using open ( ) member function:
file_stream_class stream_object;
stream_object.open (“file_name”);
 Example:
ofstream outfile;
outfile.open (“data”);
outfile.open (“text1.dat”);
12

Opening Files
Opening files using open( ):
 To open a file for both input and output, we declare
objects of fstream class.
 Syntax for fstream class using Constructor:
fstream fstream-object(“file name”, mode);
 syntax for open( ) member function:
fstream-object.open(“file name”, mode);
 Example:
fstream outfile;
outfile.open (“text1.dat”, mode);
13

File Modes
File Modes:
 While using constructors or open( ), the files were created
or opened in the default mode.
 There was only one argument passed, i.e. the filename.
 C++ provides a mechanism of opening a file in different
modes in which case the second parameter must be
explicitly passed.
 Syntax:
stream_object.open(“filename”, mode);
 Example:
fout.open(“data”, ios::app); //opens in append mode
14

File Modes
The lists of file modes are:
15
Mode method Stream Type Meaning
ios::app ofstream append to end of the file at opening time
ios::in ifstream open file for reading
ios::out ofstream open file for writing
ios::ate ifstream Open file for updating and move the file
pointer to the end of file
ios::trunc ofstream On opening, delete the contents of file
ios::nocreate ofstream Turn down opening if the file does not
exists
ios::binary ifstream Opening a binary file.

File Modes
Example of opening file:
16

Closing File
Closing File:
 The member function close( ) on its execution removes the
linkage between the file and the stream object.
 Syntax:
stream_object.close( );
 Example:
ofstream_obj.close( );
ifstream_obj.close( );
17

Operation in text file
Input and output operation in text file:
 The data in text files are organized into lines with new
line character as terminator.
 Text file need following types of character input and
output operations:
 put( ) function
 get( ) function
 getline( ) function
18

Text files
put( ) function in text file:
 The put( ) member function belongs to the class ofstream
and writes single character to the associated stream.
 Syntax:
ofstream_object.put(ch); // ch is the character variable.
 Example:
char ch=’A’;
ofstream fout(“text.txt”);
fout.put(ch);
 fout is the object of ofstream.
 Text is the name of the file.
 Value at ch is written to text.
19

Text files
get( ) function in text file:
 The get( ) member function belong to the class ifstream
and reads a single character from the associated stream.
 Syntax:
ifstream_object.get (ch); // ch is the character variable.
 Example:
char ch=’A’;
ifstream fin(“text.txt”);
fin.get (ch);;
 fin is the object of ifstream.
 Text is the name of the file.
 Value at ch is written to text.
20

Text files
getline( ) function in text file:
 The getline( ) member function belong to the class
ifstream, it reads a whole line from the associated stream.
 Syntax:
fin.getline(buffer, SIZE)
It reads SIZE characters from the file represented by the object fin or till the
new line character is encountered, whichever comes first into the buffer.
 Example:
char Student[SIZE];
ifstream fin;
fin.getline (Student, SIZE);
21

Binary files
Input and output operation in binary files:
 Binary files are very much use when we have to deal with
database consisting of records.
 The binary format is more accurate for storing the
numbers as they are stored in the exact internal
representation.
 There is no conversion while saving the data and hence it
is faster.
 Functions used to handle data in binary form are:
 write ( ) member function.
 read ( ) member function
22

Binary files
write ( ) member function in binary files:
 The write( ) member function belongs to the class ofstream and
which is used to write binary data to a file.
 These functions take 2 arguments.
 First is the address of the variable
 Second the size of the variable in bytes.
 Syntax:
ofstream_object.write((char *) & variable, sizeof(variable));
 The address of the variable must be type casted to pointer to character.
 Example: student s;
ofstream fout(“std.dat”, ios::binary);
fout.write((char *) &s, sizeof(s));
23

Binary files
Detecting End of file eof( ):
 Detecting end of file is necessary for preventing any further
attempt to read data from the file.
 eof( ) is a member function of ios class.
 It returns a non-zero (true) value if the end of file condition is
encountered while reading; otherwise returns a zero (false).
 Example:
ifstream fin;
if(fin.eof( ))
{ statements; }
 This is used to execute set statements on reaching the end of the file by
the object fin.
24

File pointers
File pointers and their manipulation:
 In C++, the file I/O operations are associated with the two
file pointers:
 Input pointer (get pointer)
 Output pointer (put pointer)
 We use these pointers to move through files while reading
or writing.
 Each time an input or output operation takes place,
appropriate pointer is automatically advanced.
25

File pointers
File pointers and their manipulation:
 There are three modes under which we can open a file:
 Read only mode:
 Write only mode
 Append mode
 When a file is opened in read only mode, the input pointer is
automatically set at the beginning of the file.
 When a file is opened in write only mode, the existing
contents are deleted and output pointer is set at the beginning
 If we want to open an existing file to add more data, the file is
opened in append mode. This moves the file pointer to the end
of the file.
26

File pointers
Functions for manipulation of file pointers:
 To move file pointers to any desired position inside a file,
file stream classes support the following functions:
 seekg() - Moves get file pointer to a specific location
 seekp() - Moves put file pointer to a specific location
 tellg() - Returns the current position of the get pointer
 tellp() - Returns the current position of the put pointer
 The seekp() and tellp() are member functions of ofstream
 The seekg() and tellg() are member functions of ifstream.
 All four functions are available in the class fstream. 27

File pointers
seekg( ) file pointers:
28

File pointers
seekg(offset, seekdir) file pointers:
 The seekg(offset, seekdir) has two arguments: offset and
seekdir.
 The offset indicates the number of bytes the get pointer is to be
moved from seekdir position.
 Syntax:
stream_objectname.seekg(offset, origin_value);
 Example:
29
seekg( ) function option Action performed
object.seekg(0, ios::beg) Take get pointer to the beginning of the file
object.seekg(0, ios::cur) Stay get pointer at the current position.
object.seekg(-m, ios::end) Go backward by m bytes from the file end.

File pointers
seekg(offset, seekdir) file pointers:
30

File pointers
seekp() file pointers:
 Move the put pointer to a specified location from the beginning
of a file.
 There are two types:
 seekp(long);
 seekp(offset, seekdir);
 The seekp(long) moves the put pointer to a specified location
from the beginning of a file.
 Example:
infile.seekp(20);
31

File pointers
tellg ( ) and tellp( )file pointers:
 tellg( ) returns the current position of the get pointer.
 Syntax:
position = ifstream_object.tellg( );
 Example:
int position= fin.tellg();
 tellp( ) returns the current position of the put pointer.
 Syntax:
position = ifstream_object.tellp( );
 Example:
int position = fin.tellp();
32

File pointers
tellp( )file pointers:
33

File pointers
Functions for Manipulation of file pointers:
34

Operation on binary file
Basic operation on binary file in C++:
 Searching
 Appending data
 Inserting data in sorted files
 Deleting a record
 Modifying data.
35

Data file handling

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