File Handling In C++

SYLLABUS OUTLINE Data File Handling: Need for a data file, Types of data files – Text file and Binary file; Text File : Basic file operations on text file: Creating/Writing text into file, Reading and manipulation of text from an already existing text File (accessing sequentially); Binary File : Creation of file, Writing data into file, Searching for required data from file, Appending data to a file, Insertion of data in sorted file, Deletion of data from file, Modification of data in a file; Implementation of above mentioned data file handling in C++; Components of C++ to be used with file handling:

Header file : fstream.h; ifstream, ofstream, fstream classes; Opening a text file in in, out, and app modes; open(), get(), put(), getline() and close() functions; Detecting end-of-file (with or without using eof() function); Opening a binary file using in, out, and app modes; open(), read(), write() and close() functions; Detecting end-of-file (with or without using eof() function); tellg(), tellp(), seekg(), seekp() functions SYLLABUS OUTLINE (Contd.)

All programs we looked earlier: Introduction input data from the keyboard . output data to the screen. Difficult to handle large amount of input data. Output would also be lost as soon as we exit from the program. How do we store data permanently?. We can use secondary storage device. Data is packaged up on the storage device as data structures called files .

Files (Streams) Files are used to store data in a relatively permanent form, on floppy disk, hard disk, tape or other form of secondary storage. Files can hold huge amounts of data if need be. Ordinary variables (even records and arrays) are kept in main memory which is temporary and rather limited in size. Lets put it in points…………..

Why use files? Convenient way to deal with large quantities of data. Store data permanently (until file is deleted). Avoid having to type data into program multiple times. Share data between programs.

The following is a comparison of the two types of storage………..

Main memory Made up of RAM chips. Used to hold a program when it is running, including the values of its variables (whether integer, char, an array, etc.) Secondary memory Usually a disk drive (or magnetic tape). Used to hold files (where a file can contain data, a program, text, etc.) Can hold rather large amounts of data.

Main memory Can only hold relatively small amounts of data. Is temporary (as soon as the program is done or the power goes out all of these values are gone). Gives fast access to the data (all electronic ). Secondary memory Can hold rather large amounts of data. Is fairly permanent . (A file remains even if the power goes out. It will last until you erase it, as long as the disk isn't damaged, at least.) Access to the data is considerably slower (due to moving parts).

I/O in C++ I/O in C++ uses streams A Stream is a general name given to flow of data.

Flow of Data…. PROGRAM DEVICES OR FILES Input Stream >> Output Stream << Data Data istream class ostream class (Insertion operator)‏ (Extraction operator)‏

More About Files….. Now we need to know: how to " connect " file to program how to tell the program to read data how to tell the program to write data error checking and handling eof

I/O in C++ Different streams are used to represent different kinds of data flow. Each stream is associated with a particular class , which contains member functions and definitions for dealing with that particular kind of data flow.

The following classes in C++ have access to file input and output functions: ifstream ofstream fstream File Related Classes

The Stream Class Hierarchy ios istream get()‏ getline()‏ read()‏ >> ostream put()‏ write()‏ << fstreambase iostream Ifstream Open()‏ Tellg()‏ Seekg()‏ Ofstream Open()‏ Tellp()‏ Seekp()‏ fstream NOTE : UPWARD ARROWS INDICATE THE BASE CLASS

OPENING A FILE 1. By using the CONSTRUCTOR of the stream class. ifstream transaction(“sales.dly”); ofstream result(“result.02”); 2. By using the open() function of the stream class ifstream transaction; transaction.open(“sales.dly”); (Associating a stream with a file)‏

File Mode Parameters PARAMETER MEANING ios::app Append to end-of file ios::ate goto end of file on opening ios::binary binary file ios::in Open existing file for reading ios::nocreate open fails if file doesn’t exist ios::noreplace open fails if file already exists ios::out creates new file for writing on ios::trunc Deletes contents if it exists The mode can combine two or more modes using bit wise or ( | )

Checking For Successful File Opening ifstream transaction(“sales.dly”); if (transcation == NULL)‏ { cout<<“unable to open sales.dly”; cin.get(); // waits for the operator to press any key exit(1); }

Closing of File Stream_name.close(); e.g., transaction.close(); fl.close(); Note : There is no need to give the physical file name at the time of closing a file.

Types of Files The two basic types of files are Text files & Binary files

Text Files A text file consists of readable characters separated into lines by newline characters. (On most PCs, the newline character is actually represented by the two-character sequence of carriage return (ASCII 13), line feed (ASCII 10). (\n)

A binary file stores data to disk in the same form in which it is represented in main memory. If you ever try to edit a binary file containing numbers you will see that the numbers appear as nonsense characters. Binary Files

Not having to translate numbers into a readable form makes binary files somewhat more efficient . Binary files also do not normally use anything to separate the data into lines. Such a file is just a stream of data with nothing in particular to separate components. Binary Files

When using a binary file we write whole record data to the file at once. but the numbers in the binary file will not be readable in this way. When using a text file, we write out separately each of the pieces of data about a given record. The text file will be readable by an editor Text Files Binary Files

for the text file we will use the usual output operator(<<) and will output each of the pieces of the record separately. with the text file we will read each of the pieces of record from the file separately, using the usual input operator(>>) For the binary file we will use write to write to the file, With the binary file we will use the read function to read a whole record, The programs to create the data files will differ in how they open the file and in how they write to the file.

: Sequential access . With this type of file access one must read the data in order, much like with a tape, whether the data is really stored on tape or not. Random access (or direct access ). This type of file access lets you jump to any location in the file, then to any other, etc., all in a reasonable amount of time. Types of File Access

FILE POINTERS Each file object has two integer values associated with it : get pointer put pointer These values specify the byte number in the file where reading or writing will take place.

File pointers….. By default reading pointer is set at the beginning . By default writing pointer is set at the end (when you open file in ios::app mode)‏ There are times when you must take control of the file pointers yourself so that you can read from and write to an arbitrary location in the file.

Functions associated with file pointers : The seekg() and tellg() functions allow you to set and examine the get pointer . The seekp() and tellp() functions allow you to set and examine the put pointer .

seekg() function : (with one argument) With one argument : fl.seekg(k); fl.seekp(k); where k is absolute position from the beginning. The start of the file is byte 0 It will result in moving the pointer as shown- Begin File End k bytes ^ File pointer

‘ seek’ functions : ( With two arguments ) Number of bytes file pointer to be moved Location from where File pointer is to be moved fl.seekg(offset, refposition); fl.seekp(offset, refposition); Refposition takes one of the following forms : ios::beg Start of the file ios::cur current position of the pointer ios::end End of the file

File Pointer offset calls fl.seekg(0,ios::beg); Go to start fl.seekg(0,ios::cur); Stay at the current position fl.seekg(0,ios::end); Go to the end of file fl.seekg(m,ios::beg); Move to (m+1)th byte in the file

File Pointer offset calls fl.seekg(m,ios::cur); Go forward by m bytes from current pos fl.seekg(-m,ios::beg); Go backward by m bytes from current pos fl.seekg(-m,ios::cur); Go backward by m bytes from the end

seekg() function : ( With two arguments ) : Go backward by m bytes from the end m bytes fl.seekg(m,ios::cur); Go forward by m bytes from current pos fl.seekg(m,ios::beg); Move to (m+1)th byte in the file m bytes Begin End End Begin m bytes Begin End ^ Offset from Begin ^ Offset from current position ^ Offset from end fl.seekg(-m,ios::cur);

EXAMPLES Creation of a text file

#include <fstream.h> #include <conio.h> #include <stdio.h> void main()‏ { clrscr(); char c,d,ans; char str[80]; ofstream outfl("try.txt"); do { cout<<"please give the string : "; gets(str); outfl<<str; cout <<"do you want to write more...<y/n> : "; ans=getch(); } while(ans=='y'); outfl<<'\0'; outfl.close(); clrscr(); ifstream infl; getch(); cout <<"reading from created file \n"; infl.open("try.txt"); out.open("cod.dat"); //********************************** c=infl.get(); do { d=c+1; cout<<c<<d<<'\n'; out.put(d); c= infl.get(); } while (c!='\0'); out<<'\0'; infl.close(); outfl.close(); getch(); //********************************* } Program to generate coded file…… (Text File)

File Handling In C++

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File Handling In C++