file handling - n k upadhyay

DATE:- 26/05/16

Presented By: Nitin Kumar Upadhyay K.V. Ramgarh Cantt

Region:- Ranchi

What is File and what is the purpose of using a File?

A file can be defined as bunch of bytes stored on some storage media.

Files are used to store data permanently in C++.

What is Stream and how I/O Operations takes place in a file?

A stream is a sequence of bytes or flow of data.

Stream is needed to perform input and output operations in a file.

What are different types of File Streams?

There are two types of streams.

ofstream :- It is used to write data to a file.

Variable output stream File

ifstream :- It is used to read data from a file. File input stream variable

To learn Merge and Search operations first we have to understand file opening modes used for above said purpose. Q. What is file opening mode Ans. File opening Mode defines type of operations which we can perform with the file. For Merge and Search operation following modes are used. ios::out:- It creates a new file for writing. ios::in :- It opens an existing file for reading. ios::app:- It is used to open an existing file to append more data inside the file.

Functions/Operators to read/write data from a file.

Functions/Operators to read data from a file. <<, get( ), getline( ),read()

Functions/Operators to write data to a file.

>>,put( ),write( )

Functions to read and write data from a file.

S.No.

Type of Data Function for Writing data

to a file

Function for Reading Data

from a file

01 Number << >>

02 char put( ),<< get( ),>>

03 Word << >>

04 String << >>

05 Line/Sentence << get( )getline( )

06 Record read( ) write( )

To perform search operation in file.

It must be open in ios::in mode and the data must be read from file as per the type of data or requirement.For ex. (i)Suppose a question is given to count or perform any operation in file on the basis of alphabets like counting of vowels or blank spaces etc.

Then data must be read from file usingfstream.get(char_var);If stream object is f1 and char variable is ch then f1.get(ch);

To perform search operation in file.

(ii) If question is given to count no of words or occurrence of a particular word then Then data must be read from file using file_stream>>string_var; If stream object is f1 and string variable is str then f1 >> str;

To perform search operation in file.

(iii) if question is given to count no of lines present in a file. Then data must be read from file using file_stream.get(str,no_of_char,delim_char) If stream object is f1 and string variable is str then

f1.get(str,80,’\n’);or

f1.getline(str,80,’\n’);

To perform search operation in file.

(iv) if question is given to count no of records Then data must be read from file using file_stream.read((char *)&o,sizeof(o)); If stream object is f1 and structure variable/class object is o then

f1.read((char *)&o,sizeof(o));

To perform search operation in a file implemeted using structure.For example suppose stu is a structure with following definition and student.dat is a file which contains details of students as given structure.strcut stu{ int rollno; char name[30]; float per;}s;

then to search record of a student having name sumit.void search( ){ fstream f1;char str[40]; f1.open(“student.dat”,ios::in|ios::binary); while(!f1.eof( )) { f1.read((char *)&s,sizeof(s)); if(strcmp(s.name,”sumit”)==0) cout<<s.rollno<<s.percentage } f1.close( );}

To add one more record of a student.

void append( ){ fstream f1;student p; f1.open(“student.dat”,ios::app|ios::binary); while(!f1.eof( )) { cout<<“Input rollno,name and percentage”; cin>>s.rollno;gets(s.name);cin>>s.per; f1.write((char *)&s,sizeof(s)); } f1.close( );}

#include<fstream.h> #include <conio.h> #include<stdio.h> void main( ) { char ch; char str[20]; fstream f1,f2,f3; f1.open("abc1.txt",ios::out); cout<<"input str"; gets(str);

f1<<str; f1.close(); f2.open("abc2.txt",ios::out); cout<<"input str"; gets(str); f2<<str; f2.close(); f1.open("abc1.txt",ios::in); f2.open("abc2.txt",ios::in); f3.open("abc3.txt",ios::app);

while(!f1.eof()) { f1.get(ch); f3.put(ch);} while(!f2.eof()) { f2.get(ch); f3.put(ch); } f1.close(); f2.close(); f3.close(); f3.open(“abc3.txt”,ios::in); while(!f3.eof()) { f3>>(str); cout<<str } f3.close(); }}