Data
File Handling In C++ 
File. The information / data stored under a
specific name on a storage device, is called a file.
Stream. It refers to a sequence of bytes.
Text file. It is a file that
stores information in ASCII characters. In text files, each line of text is
terminated with a special character known as EOL (End of Line) character or
delimiter character. When this EOL character is read or written, certain
internal translations take place.
Binary file. It 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.
Classes
for file stream operation
ofstream: Stream class to write on files
ifstream: Stream class to read from files
fstream: Stream class to both read and write from/to files.
ifstream: Stream class to read from files
fstream: Stream class to both read and write from/to files.
Opening
a file
OPENING FILE USING CONSTRUCTOR
ofstream outFile("sample.txt"); //output only
ifstream inFile(“sample.txt”); //input only
ofstream outFile("sample.txt"); //output only
ifstream inFile(“sample.txt”); //input only
OPENING FILE USING open()
Stream-object.open(“filename”, mode)
Stream-object.open(“filename”, mode)
ofstream outFile;
outFile.open("sample.txt");
ifstream inFile;
inFile.open("sample.txt");
outFile.open("sample.txt");
ifstream inFile;
inFile.open("sample.txt");
|
File mode parameter
|
Meaning
|
|
ios::app
|
Append to end of file
|
|
ios::ate
|
go to end of file on opening
|
|
ios::binary
|
file open in binary mode
|
|
ios::in
|
open file for reading only
|
|
ios::out
|
open file for writing only
|
|
ios::nocreate
|
open fails if the file does not
exist
|
|
ios::noreplace
|
open fails if the file already
exist
|
|
ios::trunc
|
delete the contents of the file if
it exist
|
All these flags can
be combined using the bitwise operator OR (|). For example, if we want to open
the file example.bin in binary mode to add data we could do it by the following
call to member function open():
fstream
file;
file.open ("example.bin", ios::out | ios::app | ios::binary);
file.open ("example.bin", ios::out | ios::app | ios::binary);
Closing
File
outFile.close();
inFile.close();
inFile.close();
INPUT
AND OUTPUT OPERATION
put() and get() function
the function put() writes a single character to the associated stream. Similarly, the function get() reads a single character form the associated stream.
example :
file.get(ch);
file.put(ch);
the function put() writes a single character to the associated stream. Similarly, the function get() reads a single character form the associated stream.
example :
file.get(ch);
file.put(ch);
write() and read() function
write() and read() functions write and read blocks of binary data.
example:
file.read((char *)&obj, sizeof(obj));
file.write((char *)&obj, sizeof(obj));
write() and read() functions write and read blocks of binary data.
example:
file.read((char *)&obj, sizeof(obj));
file.write((char *)&obj, sizeof(obj));
ERROR
HANDLING FUNCTION
|
FUNCTION
|
RETURN VALUE AND MEANING
|
|
eof()
|
returns true (non zero) if end of
file is encountered while reading; otherwise return false(zero)
|
|
fail()
|
return true when an input or
output operation has failed
|
|
bad()
|
returns true if an invalid
operation is attempted or any unrecoverable error has occurred.
|
|
good()
|
returns true if no error has
occurred.
|
File
Pointers And Their Manipulation
All
i/o streams objects have, at least, one internal stream pointer:
ifstream, like istream, has a pointer known as the get pointer that points to the element to be read in the next input operation.
ifstream, like istream, has a pointer known as the get pointer that points to the element to be read in the next input operation.
ofstream, like ostream,
has a pointer known as the put pointer that points to the location where the
next element has to be written.
Finally,
fstream, inherits both, the get and the put pointers, from iostream (which is
itself derived from both istream and ostream).
These internal stream pointers that point to the reading or writing locations within a stream can be manipulated using the following member functions:
These internal stream pointers that point to the reading or writing locations within a stream can be manipulated using the following member functions:
|
seekg()
|
moves get pointer(input) to a
specified location
|
|
seekp()
|
moves put pointer (output) to a
specified location
|
|
tellg()
|
gives the current position of the
get pointer
|
|
tellp()
|
gives the current position of the
put pointer
|
The other prototype for these functions is:
seekg(offset,
refposition );
seekp(offset, refposition );
seekp(offset, refposition );
The parameter offset
represents the number of bytes the file pointer is to be moved from the
location specified by the parameter refposition. The refposition takes one of
the following three constants defined in the ios class.
ios::beg
start of the file
ios::cur current position of the pointer
ios::end end of the file
ios::cur current position of the pointer
ios::end end of the file
example:
file.seekg(-10, ios::cur);
file.seekg(-10, ios::cur);
Basic Operation On Text File In C++
File I/O is a
five-step process:
1. Include the header file fstream in the program.
2. Declare file stream object.
3. Open the file with the file stream object.
4. Use the file stream object with >>, <<, or other input/output functions.
5. Close the files.
1. Include the header file fstream in the program.
2. Declare file stream object.
3. Open the file with the file stream object.
4. Use the file stream object with >>, <<, or other input/output functions.
5. Close the files.
Following
program shows how the steps might appear in program.
Program to write in a text
file
#include <fstream>
using namespace std;
int main()
{
ofstream fout;
fout.open("out.txt");
char str[300] = "Time is a great teacher but
unfortunately it kills all its pupils. Berlioz";
//Write string to the file.
fout << str;
fout.close();
return 0;
}
Program to read from text file
and display it
#include<fstream>
#include<iostream>
using namespace std;
int main()
{
ifstream fin;
fin.open("out.txt");
char ch;
while(!fin.eof())
{
fin.get(ch);
cout << ch;
}
fin.close();
return 0;
}
Program to count number of
characters.
#include<fstream>
#include<iostream>
using namespace std;
int main()
{
ifstream fin;
fin.open("out.txt");
int count = 0;
char ch;
while(!fin.eof())
{
fin.get(ch);
count++;
}
cout << "Number of characters in file are " << count;
fin.close();
return 0;
}
Program to count number of
words
#include<fstream>
#include<iostream>
using namespace std;
int main()
{
ifstream fin;
fin.open("out.txt");
int count = 0;
char word[30];
while(!fin.eof())
{
fin >> word;
count++;
}
cout << "Number of words in file are " << count;
fin.close();
return 0;
}
Program to count number of
lines
#include<fstream>
#include<iostream>
using namespace std;
int main()
{
ifstream fin;
fin.open("out.txt");
int count = 0;
char str[80];
while(!fin.eof())
{
fin.getline(str,80);
count++;
}
cout << "Number of lines in file are " << count;
fin.close();
return 0;
}
Program to copy contents of
file to another file.
#include<fstream>
using namespace std;
int main()
{
ifstream fin;
fin.open("out.txt");
ofstream fout;
fout.open("sample.txt");
char ch;
while(!fin.eof())
{
fin.get(ch);
fout << ch;
}
fin.close();
fout.close();
return 0;
}
Basic
Operation On Binary File In C++
When data is stored
in a file in the binary format, reading and writing
data is faster because no time is lost in converting the data from one format to another format. Such files are called binary files. This following program explains how to create binary files and also how to read, write, search, delete and modify data from binary files.
data is faster because no time is lost in converting the data from one format to another format. Such files are called binary files. This following program explains how to create binary files and also how to read, write, search, delete and modify data from binary files.
#include<iostrea.h>
#include<fstream.h>
#include<cstdio.h>
class Student
{
int admno;
char name[50];
public:
void setData()
{
cout << "\nEnter admission no. ";
cin >> admno;
cout << "Enter name of student ";
cin.getline(name,50);
}
void showData()
{
cout << "\nAdmission no. : " << admno;
cout << "\nStudent Name : " << name;
}
int retAdmno()
{
return admno;
}
};
/*
* function to write in a binary file.
*/
void write_record()
{
ofstream outFile;
outFile.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();
}
/*
* 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)
{
outFile.write((char*)&obj, sizeof(obj));
}
}
inFile.close();
outFile.close();
remove("student.dat");
rename("temp.dat", "student.dat");
}
/*
* function to modify a record
*/
void modify_record(int n)
{
fstream file;
file.open("student.dat",ios::in | ios::out);
Student obj;
while(file.read((char*)&obj, sizeof(obj)))
{
if(obj.retAdmno() == n)
{
cout << "\nEnter the new details of student";
obj.setData();
int pos = -1 * sizeof(obj);
file.seekp(pos, ios::cur);
file.write((char*)&obj, sizeof(obj));
}
}
file.close();
}
int main()
{
//Store 4 records in file
for(int i = 1; i <= 4; i++)
write_record();
//Display all records
cout << "\nList of records";
display();
//Search record
cout << "\nSearch result";
search(100);
//Delete record
delete_record(100);
cout << "\nRecord Deleted";
//Modify record
cout << "\nModify Record 101 ";
modify_record(101);
return 0;
}
