basics of file handling

Basics of File
Handling
Name-Pinkpreet Kaur
Section-N1
Roll no.-115329

Contents of presentation
 Using input/output files
 General files I/O steps
 Using input/output files
 Streams
 Predifined console streams
 File modes
 File pointers
 Binary file operations

Using Input/Output Files
 Files in C++ are interpreted as a sequence of bytes stored on
some storage media.
 The data of a file is stored in either readable form or in binary
code called as text file or binary file.
 The flow of data from any source to a sink is called as a stream
 Computer programs are associated to work with files as it helps
in storing data & information permanently.
 File - itself a bunch of bytes stored on some storage devices.
 In C++ this is achieved through a component header file called
fstream.h
 The I/O library manages two aspects- as interface and for
transfer of data.
 The library predefine a set of operations for all file related
handling through certain classes.

A computer file
 is stored on a secondary storage device
(e.g., disk);
 is permanent;
 can be used to provide input data to a
program or receive output data from a
program, or both;
 must be opened before it is used.

General File I/O Steps
 Declare a file name variable
 Associate the file name variable with the disk
file name
 Open the file
 Use the file
 Close the file

 Streams act as an interface between files and programs. In C++ .
A stream is used to refer to the flow of data from a particular
device to the program’s variablesThe device here refers to files,
keyboard, console, memory arrays. In C++ these streams are
treated as objects to support consistent access interface.
 They represent as a sequence of bytes and deals with the flow of
data.
 Every stream is associated with a class having member
functions and operations for a particular kind of data flow.
 File -> Program ( Input stream) - reads
 Program -> File (Output stream) – write

 All designed into fstream.h and hence needs to be included in all
file handling programs.
 Diagrammatically as shown in next slide

 stream - a sequence of characters
 interactive (iostream)
 cin - input stream associated with keyboard.
 cout - output stream associated with display.
 file (fstream)
 ifstream - defines new input stream (normally associated
with a file).
 ofstream - defines new output stream (normally associated
with a file).

• Stream of bytes to do input and output to different devices.
• Stream is the basic concepts which can be attached to files, strings, console
and other devices.
• User can also create their own stream to cater specific device or user defined

Streams
 A stream is a series of bytes, which act either as a
source from which data can be extracted or as a
destination to which the output can be sent. Streams
resemble the producer and consumer model
 The producer produces the items to be consumed by
the consumer. The producer and the consumers are
connected by the C++ operators >> or <<. For
instance , the keyboard exhibits the nature of only a
producer,printer or monitor screen exhibit the nature
of only a consumer. Whereas , a file stored on the
disk , can behave as a producer or consumer,
depending upon the operation initiated on it.

Predefined console streams
C++ contains several predefined streams that are
opened automatically when the execution of a
program starts.
1) cin :standard input (usually keyboard) corresponding
to stdio in C
2) cout :standard output (usually screen) corresponding
to stdout in C
3) cerr :standard error output (usually screen)
corresponding to stderr in C
4) clog : A fully buffered version of cerr (No C equivalent)

Why to use Files
 Convenient way to deal large quantities of
data.
 Store data permanently (until file is deleted).
 Avoid typing data into program multiple times.
 Share data between programs.
 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

File Modes
Name Description
ios::in Open file to read
ios::out Open file to write
ios::app All the date you write, is put at the end of the file.
It calls ios::out
ios::ate All the date you write, is put at the end of the file.
It does not call ios::out
ios::trunc Deletes all previous content in the file. (empties
the file)
ios::nocreate If the file does not exist, opening it with the open()
function gets impossible.
ios::noreplace If the file exists, trying to open it with the open()
function, returns an error.
ios::binary Opens the file in binary mode.

File Modes
 Opening a file in ios::out mode also opens it in the
ios::trunc mode by default. That is, if the file already
exists, it is truncated
 Both ios::app and ios::ate set the pointers to the end
of file, but they differ in terms of the types of
operations permitted on a file. The ios::app allows to
add data from end of file, whereas ios::ate mode
allows to add or modify the existing data anywhere in
the file. In both the cases the file is created if it is non
existent.
 The mode ios::app can be used only with output files
 The stream classes ifstream and ofstream open files
in read and write modes by default.

File pointers
 Each file has two associated pointers known as the file pointers.

One of them is called the input pointer or get pointer.
The get pointer specifies a location from which the current reading
operation is initiated
Other is called the output pointer or put pointer.
The put pointer specifies a location from where the current writing
operation is initiated
We can use these pointers to move through the files while reading or
writing.
The input pointer is used for reading the contents of a given file
location and the output pointer is used for writing to a given file
location.
Functions for manipulation of file pointers
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.

File Open Mode
#include <fstream>
int main(void)
{
ofstream outFile("file1.txt", ios::out);
outFile << "That's new!n";
outFile.close();
Return 0;
}

If you want to set more than one open mode, just use the
OR operator- |. This way:

ios::ate | ios::binary

Dealing with Binary files
 Functions for binary file handling
get(): read a byte and point to the next byte to
read
put(): write a byte and point to the next location for
write
read(): block reading
write(): block writing

flush():Save data from the buffer to the output file.

Reading /Writing from/to Textual Files

#include <fstream.h>
To write: main()
put() – writing single character {
<< operator – writing an object // Writing to file
ofstream OutFile("my_file.txt");
To read:
OutFile<<"Hello "<<5<<endl;
get() – reading a single character of a OutFile.close();
buffer
getline() – reading a single line int number;
>> operator – reading a object char dummy[15];

// Reading from file
ifstream InFile("my_file.txt");
InFile>>dummy>>number;

InFile.seekg(0);

InFile.getline(dummy,sizeof(dummy));
InFile.close();
}

Binary file operations
In connection with a binary file, the file mode must
contain the ios::binary mode along with other
mode(s)

To read & write a or on to a binary file,
as the case may be blocks of data are accessed
through
the use of C++ read() and write() respectively.

Handling binary data

#include <fstream>
using namespace std;

int main(){

ifstream in(“binfile.dat”);
ofstream out(“out.dat”);
if(!in || !out) { // return}
unsigned int buf[1024];
while(!in){
in.read(buf, sizeof(unsigned
int)*1024);
out.write(buf, sizeof(unsigned
int)*1024);
}

basics of file handling

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basics of file handling