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Chapter 12- Data File Handling, , II PUC, MDRPUC, Hassan, , Chapter-12, DATA FILE HANDLING,  Introduction:, , , 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., , , , If bytes flow from main memory to devices like a display screen, a printer etc. this is called output, operation., , , , In C++, file input/output facilities are implemented through a header file fstream.h., ,  Stream in C++:, , , A stream is sequence of bytes. In C++, a stream is a general name given to flow of data., , , , Different streams are used to represent different kinds of data flow., , , , The three streams in C++ are as follows., o Input Stream: The stream that supplies data to the program is known as input stream., o Output Stream: The stream that receives data from the program is known as output, stream., o Error Stream: Error streams basically an output stream used by the programs to the file or, on the monitor to report error messages., , 1|Page, , Keerthi Kumar H M

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Chapter 12- Data File Handling, , II PUC, MDRPUC, Hassan, ,  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 and 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., ,  Classes for file stream operation:, Class, filebuf, , Meanings, It sets the file buffer to read and write, It supports operations common to the file streams. It serves as a base class for the, , fstreambase, , derived classes ifstream,ofstream and fstream and contains open( ) and close( ), as member functions, , ifstream, , ofstream, , It supports input operations. It contains open( ) with default input mode and, inherits get( ), getline( ), read( ), seekg( ) and tellg( ) functions from istream., It supports output operations. It contains open( ) with default output mode and, inherits put( ), seekp( ), tellp( ) and write( ) functions from ostream, It supports simultaneous input and output operations. It contains open( ) with, , fstream, , default input mode and inherits all the functions from istream and ostream, classes through iostream, ,  Types of data Files:, , , Generally there are two types of files in C++:, , 2|Page, , Keerthi Kumar H M

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Chapter 12- Data File Handling, , II PUC, MDRPUC, Hassan, ,  Text Files:, o A text file is a file that stores the information in ASCII characters., o Each line of text is terminated by a special character, known as End of Line (EOL) or delimiter.,  Binary Files:, o A binary file is a file that contains information in the same format as it is held in memory., o In binary files, no delimiters are used for a line and no translations occur here., ,  Opening and Closing of 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., o Opening file using constructor., o 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., ,  Opening files using Constructors:, , , 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”), , The syntax of opening a file for output purpose only using an object ofstream class and the, constructor is as follows:, ofstream, , ofstream_object(“file name”);, , , , Example: ofstream fout (“results.dat”);, , , , The syntax of opening a file for input purpose only using an object ifstream class and the, constructor is as follows:, ifstream, , , , ifstream_object(“file name”);, , Example: ifstream fin (“results.dat”);, ,  Opening files using open( ):, , , open( ) can be used to open multiple files that use the same stream object., , , , The syntax for opening a file using open ( ) member function is as follows:, file_stream_class, , stream_object;, , stream_object.open (“file_name”);, 3|Page, , Keerthi Kumar H M

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Chapter 12- Data File Handling, , , , II PUC, MDRPUC, Hassan, , The syntax of opening a file for output purpose only using an object ofstream class and open( ), member function is as follows:, oftream_object.open(“file name”);, , , , Example: ofstream, , outfile;, , outfile.open (“data”);, outfile.open (“text.dat”);, , , The syntax of opening a file for input purpose only using an object ifstream class and open( ), member function is as follows:, iftream_object.open(“file name”);, , , , Example: ifstream ifile;, ifile.open (“data”);, , , , To open a file for both input and output, we declare objects of fstream class. We know that the, class fstream is derived from both ifstream and ofstream,, , , , The syntax for opening a file an object of type fstream class and the constructor is as follows:, fstream fstream-object(“file name’, mode);, , , , The syntax for opening a file an object of type fstream class and the open( ) member function is as, follows:, fstream-object.open(“file name’, mode);, , Important, 3 Marks, ,  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:, , , , Example:, , , , The lists of file modes are:, , stream_object.open(“filename”, mode);, fout.open(“data”, ios::app), , Mode method, ios::app, , Meaning, , Stream Type, , append to end of the file at opening time, , ofstream, , ios::in, , open file for reading, , ifstream, , ios::out, , open file for writing, , ofstream, , ios::ate, 4|Page, , // This opens the file data in the append mode., , Open file for updating and move the file, pointer to the end of file, , ifstream, Keerthi Kumar H M

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Chapter 12- Data File Handling, , ios::trunc, , II PUC, MDRPUC, Hassan, , On opening, delete the contents of file, , ofstream, , ios::nocreate, , Turn down opening if the file does not exists, , ofstream, , ios::noreplace, , Turn down opening if the file already exists, , ofstream, , Opening a binary file., , ifstream, , ios::binary, Example:, , fstreamfout (“text”, ios::out);, , // open text in output mode, , fstream fin(“text”, ios::in);, , // open text in input mode, , fout.open(“data”, ios::app), , // This opens the file data in the append mode, , fout.open(“data”, ios::app | ios::nocreate), // This opens the file in the append mode but fails to open if it does not exist, ,  Closing File:, , , The member function close( ) on its execution removes the linkage between the file and the stream, object., , , , Syntax:, , , , Example: ofstream.close( );, , stream_object.close( );, , ifstream.close( );, ,  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:, o put( ) function, o get( ) function, , Important, 3 Marks, ,  put ( ):, , , The put( ) member function belongs to the class ofstream and writes single character to the, associated stream., , , , Syntax:, , , , Example: char ch=’A’;, , ofstream_object.put(ch);, , // where ch is the character variable., , 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., ,  get( ):, , , The get( ) member function belong to the class ifstream and reads a single character from the, associated stream., , 5|Page, , Keerthi Kumar H M

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Chapter 12- Data File Handling, , , , Syntax:, , , , Example: char ch;, , ifstream_object.get (ch);, , II PUC, MDRPUC, Hassan, , // where ch is the character variable., , ifstream fin(“text.txt”);, fin.get (ch);, , , fin is the object of ifstream. Text is the name of the file. Reads a character into the variable ch., ,  getline( ):, , , It is used to read a whole line of text. It belongs to the class ifstream., , , , Syntax:, , , , It reads SIZE characters from the file represented by the object fin or till the new line character is, , fin.getline(buffer, SIZE), , encountered, whichever comes first into the buffer., , , Example:, char book[SIZE];, ifstream fin;, fin.getline (book, SIZE);, ,  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:, , Important, 3 Marks, , o write ( ) member function., o read ( ) member function,  write ( ):, , , The write ( ) member function belongs to the class ofstream and which is used to write binary data, to a file., , , , Syntax:, , , , These functions take 2 arguments. The first is the address of the variable and second the size of the, , ofstream_object.write((char *) & variable, sizeof(variable));, , variable in bytes. 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));, , 6|Page, , Keerthi Kumar H M

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Chapter 12- Data File Handling, , II PUC, MDRPUC, Hassan, ,  read ( ):, , , The read ( ) member function belongs to the class ifstream and which is used to read binary data, from a file., , , , Syntax:, , , , These functions take 2 arguments. The first is the address of the variable and second the size of the, , ifstream_object.read((char *) & variable, sizeof(variable));, , variable in bytes. The address of the variable must be type casted to pointer to character., , , Example:, , student s;, ifstream fin(“std.dat”, ios::binary), fin.write((char *) &s, sizeof(s));, ,  Detecting End of file:, , , 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., ,  File pointers and their manipulation:, , , In C++, the file I/O operations are associated with the two file pointers:, o Input pointer (get pointer), o 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., o ifstream, like istream, has a pointer known as get pointer that points to the element to be read, in the next input operation., o ofstream, like ostream, has a pointer known as put pointer that points to the location where the, next element has to be written., , , , There are three modes under which we can open a file:, o Read only mode, , 7|Page, , Keerthi Kumar H M

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Chapter 12- Data File Handling, , II PUC, MDRPUC, Hassan, , o Write only mode, o Append mode, , , , When we open a file in read only mode, the input pointer is automatically set at the beginning so, that we read the file from the beginning., , , , When we open a file 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., ,  Functions for manipulation of file pointers:, , , To move file pointers to any desired position inside a file, file stream classes support the following, functions., o seekg(), , -, , Moves get file pointer to a specific location, , o seekp(), , -, , Moves put file pointer to a specific location, , o tellg(), , -, , Returns the current position of the get pointer, , o, , -, , Returns the current position of the put pointer, , tellp(), , , , 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., , Important, 3 Marks, ,  seekg( ):, , , Move the get pointer to a specified location from the beginning of a file., , , , There are two types:, o seekg(long);, o seekg(offset, seekdir);, , , , The seekg(long) moves the get pointer to a specified location from the beginning of a file., , 8|Page, , Keerthi Kumar H M

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Chapter 12- Data File Handling, , II PUC, MDRPUC, Hassan, , , , Example: inf.seekg(20);, , , , 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., , , , seekdir takes one of the following three seek direction constants., Constant, , Meaning, , ios::beg, , seek from beginning of file, , ios::cur, , seek from current location, , ios::end, , seek from end of file, , , , Syntax:, , , , Example : Some of the pointer offset calls and their actions are shown in the following table, , stream_objectname.seekg(offset, origin_value);, , seekg( ) function option, , Action performed, , object.seekg(0, ios::beg), , Take get pointer to the beginning of the file, , object.seekg(0, ios::end), , Go to end of the file, , object.seekg(0, ios::cur), , Stay get pointer at the current position., , object.seekg(m, ios::beg), , Move forward by (m+1) bytes in the file, , object.seekg(-m, ios::end), , Go backward by m bytes from the file end., ,  seekp ( ):, , , Move the put pointer to a specified location from the beginning of a file., , , , There are two types:, o seekp(long);, o seekp(offset, seekdir);, , , , The seekp(long) moves the put pointer to a specified location from the beginning of a file., , , , Example: inf.seekp(20);, , , , The seekp(offset, seekdir) has two arguments: offset and seekdir., , , , The offset indicates the number of bytes the put pointer is to be moved from seekdir position., , , , Syntax:, , stream_objectname.seekp(offset, origin_value);, , seekp( ) function option, , Action performed, , object.seekp(0, ios::beg), , Go to beginning of the file for writing, , object.seekp(0, ios::end), , Go to end of the file for writing, , object.seekp(0, ios::cur), , Stay at the current position for writing, , 9|Page, , Keerthi Kumar H M

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Chapter 12- Data File Handling, , II PUC, MDRPUC, Hassan, , object.seekp(m, ios::beg), , Move forward by m bytes from the beginning for writing, , object.seekp(-m, ios::end), , Go backward by m bytes from the end for writing, ,  tellg ( ) and tellp( ):, , , tellg( ) returns the current position of the get pointer., , , , Syntax:, , , , Example: int position, , position = ifstream_object.tellg( );, , position= fin.tellg();, , , tellp( ) returns the current position of the put pointer., , , , Syntax:, , , , Example: int position, , position = ifstream_object.tellp( );, , position= fin.tellp();, ,  Basic operation on binary file in C++:, , , Basic operation on binary file is:, o Searching, o Appending data, o Inserting data in sorted files, o Deleting a record, o Modifying data, CHAPTER 12 – DATA FILE HANDLING BLUE PRINT, VSA (1 marks), , SA (2 marks), , LA (3 Marks), , Essay (5 Marks), , Total, , -, , 01 Question, , 01 Question, , -, , 02 Question, , -, , Question no 15, , Question no 23, , -, , 05 Marks, , Important Questions, 2 Marks Question:, 1. Differentiate between ifstream and ofstream., , [March 2015], , 2. What is a stream? Mention any one stream used in C++., , [June 2015], , 3. Write any two member functions belonging to of stream class., , [March 2016], , 4. Write any two member functions belonging to if stream class., , [June 2016], , 5. Differentiate between read( ) and write( )., , [March 2017], , 6. Differentiate between put( ) and get( ) functions with reference to binary files., 10 | P a g e, , [June 2017], , Keerthi Kumar H M

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Chapter 12- Data File Handling, , II PUC, MDRPUC, Hassan, , 3 Marks Question:, 1. Give the function of put( ), get( ) and getline( ) with respect to text files., 2. List the fifferent modes of opening a file with their meaning in C++., 3. Give the functions for the following:, a. get( ), , b. getline( ), , [March 2015], [June 2015], [March 2016], , c. read( ), , 4. Mention the types of data files. Explain., 5. Explain any three modes of to open a file in C++., 6. Write the member function belong to ifstream., , [June 2016], [March 2017], [June 2017], , ****************, , 11 | P a g e, , Keerthi Kumar H M