Data File Handling in C++
What is File?
A file is a stream of bytes stored on some secondary storage
devices.
There are two type of data file-
1. Text file
2. Binary file
1. Text file
A text file
stores information in the readable and printable form. Each line of text
is terminated with an EOL(End of line character).
2. Binary File
A binary file contains information in the
non-readable i.e. in some format in which it is held in memory.
Stream
A stream is used to name flow of data. There are three file
I/O classes used for file read/write.
1. ifstream - used for
read operation
2. ofstream - used for
write operation
3. fstream - used for both
read/write
fstream.h
This header file includes the definition of stream classes
ifstream, ofstream, fstream. It contains predefined set of operation for
handling file.
A file can be opened
1. By the constructor method
This method is preferred when file is
opened in input or output mode.
Ex. ofstream file(“student.dat”);
2. By the member function
It will prefer when file is opened in
various mode i.e. ios::in, ios::out, ios::app, ios::ate etc.
Ex. fstream file;
file.open(“book.txt”,ios::in|ios::out|ios::binary);
File modes
ios::out
It opens the file in output mode and place the file pointer
in beginning.
ios::in
It opens the file in read mode.
ios::app
It opens the file in write mode and place the file pointer
at the end.
ios::ate
It opens the file in read/write mode and place the file
pointer at the end of file i.e. input/output operation perform anywhere in the
file.
ios::trunc
It empties the existing file.
ios::noreplace
If file doesn’t exist, a new file gets created but if
exist, the open fails.
ios::nocreat
If file doesn’t exist, this shows no file is created and
open fails.
ios::binary
Open a file in binary mode.
eof()
This function determines end of file by returning true.
close ()
This function terminates connection between file and stream
and release memory.
Syntax
stream_object.close( );
Ex. file.close( );
#include<fstream.h>
#includes<iostreamh.>
#include<stdio.h>
void main()
{
char s [80],ch=’y’;
ofstream file (“myfile.txt”) //open my file in default
output mode
while (ch==’y’||ch==’Y’)
{
cout<<”\n
Enter line of text”;
gets(s);
file<<s;
cout<<”\n
More input y/n”;
cin>>ch;
}
file.close();
}
Text file functions
Char I/O-
get ()
Read a single character from text file and store in a
buffer.
Ex. file.get(ch);
Read the content of ‘myfile.txt’ and display it on monitor.
#include<fstream.h>
#include<iostream.h>
#include<stdio.h>
void main()
{
char ch;
ifstream file(“myfile.txt”); //open “myfile.txt” in default
input mode
while (file)
{
file.get(ch); //read the
character from file
cout<<ch;
}
file.close();
}
//end of main
put()
Writing a single character in textfile.
Ex. file.put(ch);
getline ()
Read line of text from text file.
Ex. file.getline(s,80);
Note-We can also use file>>ch for reading and
file>>ch writing in text file.
Binary File Function
read( )-read a block of binary data.
Syntax
stream_object.read((char*)&object,size_of_object));
Ex.file.read((char*)&s,sizeof(s));
write( )
Write a block of binary data on fixed number or fixed number
of bytes.
Syntax
stream_object.write(char*)&object ,sizeof(object));
Ex. file.write(char*)&, sizeof(s));
File pointer
The file pointer indicates the position in the file at which
the next input/output is occur.
Moving the file pointer for various operations, following
functions are used.
1. seekg ()
It places the file pointer to specified position in input
mode of file.
Ex. file.seekg(p,ios::beg)or file.seekg(-p,ios::end),
Or
file.seekg(p,ios::cur)
i.e. to move p byte position from beginning, end and current
position.
2. seekp()
It places the file pointer to specified position in output
mode.
Ex. file.seekp(p,ios::beg) or file.seekp(-p,ios::end)
Or file.seekp(p,ios::cur)
3. tellg()
This function returns the current working position of file
pointer in output mode.
Ex. int p=file.tellp();
Binary file operation- create, read, write, search, delete and modify.
#include<iostream.h>
#include<fstream.h>
#include<cstdio.h>
class student
{
int admno;
char name[50];
public:
void setData()
{
cout<<”\n Enter
admission no.”;
cin>>admno;
cout<<”Enter name of student”;
cin.getline(name,50);
}
void show()
{
cout<<”\n
Admission no:”<<admno;
cout<<”\n Student Name:”<<name;
}
int retAdmno()
{
Return admno;
}
};
/*function to write in binary file*/
void write_record()
{
ofstream outfile;
ostream.open(“student.dat”,ios::binary|ios::app);
student obj;
obj.setData();
outfile.write((char*)&obj,sizeof(obj));
outfile.close();
}
/*function to display records of file*/
void display()
{
ifstream infile;
infile.open(“student.dat”,ios::binary);
student obj;
while (infile.read((char*)&obj,sizeof(obj)))
{
obj.showData();
}
infile.close();
}
/*A function to search and display from binary file*/
void search(int n)
{
ifstream infile;
infile.open(“student.dat”,ios::binary);
student obj;
while infile.read((char*)&obj,sizeof(obj)))
{
if(obj.retAdmno()==n)
{
obj.showData();
}
}
infile.close();
}
/*function to delete a record*/
void delete_record(int n)
{
Student obj;
ifstream infile;
infile.open(“student.dat ”,ios::binary)
ofstream outfile;
outfile.open(“temp.dat”, ios::out|ios::binary);
while(infile.read((char*)&obj,sizeof(obj)))
{
if(obj.retAdmno()==n)
{
cout<<”\n Enter
the new detail of student”;
obj.setData();
int pos=-1*sizeof(obj);
file.seekp(pos,ios::cur);
file.write((char*)&obj,sizeof(obj));
}
}
file.close();
}
This post is about Data File Handling in C++. In the next post we will discuss the topic Pointer .
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