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File VO
A file is a bunch of bytes stored on some storage devices like hard disk, floppy disk etc. File /O and
console VO are closely related, In fact, the same class hierarchy that supports console 1/0 also
supports the file /O. To perform file /O, you must include in your program. It defines
several classes, including ifstream, ofstream and fstream. In C++, a file is opened by linking it to a
stream, There are three types of streams: input, output and inpuoutput. Before you can open a file,
you must first obtain a stream. OS
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Sma ey Text Files:
e Limitation: Inefficient for storing
non-textual data.
¢ Solution: Use ~ifstream* and
“ofstream* for reading and writing,
and libraries like Boost.lIOStreams
for advanced operations.
Binary Files:
¢ Limitation: Less human-readable
and harder to debug.
¢ Solution: Serialize structured data,
use libraries like Protocol Buffers or
JSON, and handle byte order with
libraries like Boost.Endian. Operation
OpenaFile
Read from a File
Write toa File
Close a File
Modify File Content
Seek within a File
Truncate a File
Delete a File
Description
Open an existing file or create a new one with specified access modes.
Read data from an opened file into memory.
Write data from memory to an opened file.
Release system resources associated with an opened file.
Change the data within an opened file.
Move the file pointer to a specific position within the file.
Shorten the size of an opened file.
Remove a file from the file system. How to opena file in C++
+ To read or enter data to afile, we need to open it first.
+ This can be performed with the help of ‘ifstream’ for
reading and ‘ftream’ or ‘ofstream’ ‘for writing or appending
to the file. q
N. All these three objects have open() function that is inbuilt in
them.
Syntax:
open( FileName , Mode );
e Example:- >
open(“sksfile”, ios:out);
3b a Here:
FileName — It denotes the name of file which has to
be opened.
Mode — There are different modes to opena file. Mode
Description
ioszin File opened in reading mode
ioss:out File opened in write mode
iosapp File opened in append mode
ioszate File opened in append mode but read and write performed atthe end of
the file.
ios:binary File opened in binary mode
ios:trune _| File opened in truncate mode
ios:mocreate _ | The file opens only ifit exists
ios:moreplace
The file opens only if it doesn’t exist ¢@ NOTE
In C+, we can use two modes simultaneously
with the help of OR (|) operator.
Example:-
open(‘“sksfile”, ios:out|ios:in); i
ba Program for Opening File:
#include
#include
void main()
{
fstream FileName;
FileName.open(“sksfile”, ios::out);
cout<<"File created successfully";
FileName.close();
} How to close a file in C++
« When a C++ program terminates, it automatically flushes
all the streams, release all the allocated memory and close
all the opened files. e Butitis always a good practice that a programmer should
close all the opened files before program termination.
e Wecan close an opened. file by using close() function. @ Following is the standard syntax for close() function,
which is a member of fstream, ifstream, and ofstream
objects:-
void close(); Program for Closing File:
#include
#include
void main()
{
fstream FileName;
FileName.open(‘sksftle”, ios::out);
cout<<"File created successfully";
FileName.close();
} In C++ we have mainly two
pointers i.e. a get pointer and a
put pointer for getting (ie.
reading) data from a file and
putting (Le. writing) data on the q
file respectively. These pointers help to access the file ina
random manner.
By using these pointers we can perform
both reading and writing operations
randomly in a file.
Hb Functions associated with File Pointers-
seekg()
ily
» seen) | a eh
tellp() f.
». A | seekg() is used to move the get pointer to a desired
location with respect to a reference point.
Syntax:
file : pointer.seekg (number of bytes Reference point) ;
Example:
fin.seekg(io,ios::beg); tellg( ):-
tellg() is used to know where the get pointer is in a
file.
Syntax:
file pointer tellg();
Example:
int posn = fin.tellg(); see! as
seelep() is used to move the put pointer to a desired
location with respect to a reference point.
Syntax:
file pointer.seekp(number of bytes Reference point);
Example:
fout.seekp(i0,ios::beg); tellpQ) is used to know where the put pointer is in a file.
Syntax:
file pointer -tellp(Q);
Example:
int posn=fout.tellp(); See! ae
seelep() is used to move the put pointer to a desired
location with respect to a reference point.
Syntax:
file pointer.seekp(number of bytes Reference point);
Example:
fout.seekp(io,ios::beg); The reference points are:
ios::beg — from beginning of file
ioszend — from end of file
ios::cur — from current position in the file.
