Filehandlinging cp2

Introduction
 All programs we looked earlier:
 input data from the keyboard.
 output data to the screen.
 Difficult to handle large amount of input data.
 Output would also be lost as soon as we exit

from the program.
 How do we store data permanently?.
 We can use secondary storage device.
 Data is packaged up on the storage device as data
structures called files.

Files (Streams)
 Files

are used to store data in a relatively
permanent form, on floppy disk, hard disk,
tape or other form of secondary storage.
Files can hold huge amounts of data if
need be. Ordinary variables (even records
and arrays) are kept in main memory
which is temporary and rather limited in
size.
Lets put it in points…………..

Why use files?
Convenient way to deal with large
quantities of data.
• Store data permanently (until file is
deleted).
• Avoid having to type data into
program multiple times.
• Share data between programs.
•

The following is a
comparison
of
the two types of storage………..

Main memory

•

Made up of RAM chips.

•

Used to hold a program
when it is running,
including the values of its
variables
(whether
integer, char, an array,
etc.)

Secondary memory

•

Usually a disk
magnetic tape).

drive

(or

•

Used to hold files (where a file
can contain data, a program,
text, etc.)

•

Can hold rather large amounts
of data.

Main memory

Secondary memory

•

Can only hold relatively
small amounts of data.

•

Can hold rather
amounts of data.

•

Is temporary (as soon
as the program is done
or the power goes out
all of these values are
gone).

•

•

Gives fast access to
the data (all electronic).

Is fairly permanent. (A file
remains even if the power
goes out. It will last until
you erase it, as long as
the disk isn't damaged, at
least.)

 Access

large

to the data is
considerably slower (due
to moving parts).

I/O in C++
 I/O

in C++ uses streams
 A Stream is a general name given to
flow of data.

Flow of Data….

PROGRAM
Input
Stream
>>
(Extraction
operator)
istream class

DEVICES OR
Data

FILES

Data

Output
Stream
<<
(Insertion
operator)
ostream class

More About Files…..
 Now

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

I/O in C++
 Different

streams are used to represent
different kinds of data flow.

 Each

stream is associated with a
particular class, which contains
member functions and
 definitions for dealing with that particular
kind of data flow.


File Related Classes
The following classes in C++
have access to file input and
output functions:
 ifstream
 ofstream
 fstream

The Stream Class Hierarchy
ios

NOTE : UPWARD ARROWS INDICATE
THE BASE CLASS

istream
get()
getline()
read()
>>

fstreambase

Ifstream
Open()
Tellg()
Seekg()

fstream

iostream

ostream
put()
write()
<<

Ofstream
Open()
Tellp()
Seekp()

OPENING A FILE
(Associating a stream with a file)

1. By using the CONSTRUCTOR of the
stream class.
ifstream transaction(“sales.dly”);
ofstream result(“result.02”);
2. By using the open() function of the
stream class
ifstream transaction;
transaction.open(“sales.dly”);

File Mode Parameters
PARAMETER
 ios::app
 ios::ate
 ios::binary
 ios::in
 ios::nocreate
 ios::noreplace
 ios::out
 ios::trunc

MEANING
Append to end-of file
goto end of file on opening
binary file
Open existing file for reading
open fails if file doesn’t exist
open fails if file already exists
creates new file for writing on
Deletes contents if it exists

The mode can combine two or more modes using bit wise or ( | )

Checking For Successful File
Opening
ifstream transaction(“sales.dly”);
if (transcation == NULL)
{
cout<<“unable to open sales.dly”;
cin.get(); // waits for the operator to press any key
exit(1);
}

Closing of File
Stream_name.close();
e.g., transaction.close();
fl.close();

Note : There is no need to give the physical
file name at the time of closing a file.

Types of Files
 The

two basic types of files are

 Text

files

&
 Binary

files

Text Files
A

text file consists of readable characters
separated into lines by newline
characters.

 (On

most PCs, the newline character is
actually represented by the two-character
sequence of carriage return (ASCII 13),
line feed (ASCII 10). (n)

Binary Files
A

binary file stores data to disk in the
same form in which it is represented in
main memory.



If you ever try to edit a binary file
containing numbers you will see that the
numbers
appear
as
nonsense
characters.

Binary Files
 Not

having to translate numbers into a
readable form makes binary files
somewhat more efficient.

 Binary

files also do not normally use
anything to separate the data into
lines.

 Such

a file is just a stream of data with
nothing in particular to separate
components.

Text Files
When using a text
file, we write out
separately each of
the pieces of data
about a given
record.
The text file will be
readable by an
editor

Binary Files
 When

using a
binary file we write
whole record data
to the file at once.

 but

the numbers in
the binary file will
not be readable in
this way.

The programs to create the data files will differ in how they
open the file and in how they write to the file.


for the text file we will
use the usual output
operator(<<) and will
output each of the
pieces of the record
separately.

 For the binary file we
will use write to write to
the file,



with the text file we will
read each of the pieces
of record from the file
separately, using the
usual input operator(>>)

 With the binary file we
will use the read
function to read a
whole record,

Types

of File Access

:Sequential access. With this type of file
access one must read the data in order,
much like with a tape, whether the data is
really stored on tape or not.
Random access (or direct access). This
type of file access lets you jump to any
location in the file, then to any other, etc.,
all in a reasonable amount of time.

FILE POINTERS
 Each

file object has two integer values
associated with it :
 get

pointer
 put pointer
 These

values specify the byte number
in the file where reading or writing will
take place.

File pointers…..
 By

default reading pointer is set at the
beginning.
 By default writing pointer is set at the
end (when you open file in ios::app
mode)
 There are times when you must take
control of the file pointers yourself so
that you can read from and write to an
arbitrary location in the file.

Functions associated with file
pointers :
 The

seekg() and tellg() functions allow
you to set and examine the get pointer.

 The

seekp() and tellp() functions allow
you to set and examine the put pointer.

seekg() function : (with one argument)
 With

one argument :
fl.seekg(k);
fl.seekp(k);

where k is absolute position from the beginning. The
start of the file is byte 0
It will result in moving the pointer as shownFile

Begin
k bytes

^
File pointer

End

‘seek’ functions : (With two arguments )
fl.seekg(offset, refposition);
fl.seekp(offset, refposition);
Number of bytes file
pointer to be moved

Location from where File
pointer is to be moved

Refposition takes one of the following forms :
•ios::beg Start of the file
•ios::cur current position of the pointer
•ios::end End of the file

File Pointer offset calls
•fl.seekg(0,ios::beg); Go to start
•fl.seekg(0,ios::cur); Stay at the current position
•fl.seekg(0,ios::end); Go to the end of file
•fl.seekg(m,ios::beg);Move to (m+1)th byte in the file

File Pointer offset calls
•fl.seekg(m,ios::cur);

Go forward by m bytes
from current pos

•fl.seekg(-m,ios::beg);

Go backward by m bytes
from current pos

•fl.seekg(-m,ios::cur);

Go backward by m bytes
from the end

seekg() function : (With two arguments )
:
Begin

End

•fl.seekg(m,ios::beg);
m bytes

^
Offset from Begin

Move to (m+1)th byte in the file
End

Begin

fl.seekg(-m,ios::cur);
Offset from end

^

m bytes

Go backward by m bytes from the end
End

Begin

fl.seekg(m,ios::cur);
m bytes

^

Offset from current
position

Go forward by m bytes from current pos

EXAMPLES


Creation of a text file

Program to generate coded file……
(Text File)
#include <fstream.h>
#include <conio.h>
#include <stdio.h>
void main()
{ clrscr();
char c,d,ans;
char str[80];
ofstream outfl("try.txt");
do
{ cout<<"please give the string : ";
gets(str);
outfl<<str;
cout <<"do you want to write more...<y/n> : ";
ans=getch();
} while(ans=='y');
outfl<<'0';
outfl.close();

clrscr();

ifstream infl;
getch();
cout <<"reading from created file n";
infl.open("try.txt");
out.open("cod.dat");
//**********************************
c=infl.get();
do
{ d=c+1;
cout<<c<<d<<'n';
out.put(d);
c= infl.get();
} while (c!='0');
out<<'0';
infl.close();
outfl.close();
getch();
//*********************************
}

Filehandlinging cp2

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