3. Files
• A file is a collection of data in mass storage.
• A data file is not a part of a program’s source
code.
• The same file can be read or modified by
different programs.
• The program must be aware of the format of
the data in the file.
4. Files (cont’d)
• The file system is maintained by the
operating system.
• The system provides commands and/or GUI
utilities for viewing file directories and for
copying, moving, renaming, and deleting
files.
• The system also provides “core” functions,
callable from programs, for reading and
writing directories and files.
8. Sequential Files
Sequential file techniques provide a straightforward way to read and write
files. Basic's sequential file commands manipulate text files: files of ASCII
characters with carriage-return/linefeed pairs separating records.
In computer science, sequential access means that a group of elements (e.g.
data in a memory array or a disk file or on a tape) is accessed in a
predetermined, ordered sequence. Sequential access is sometimes the only
way of accessing the data, for example if it is on a tape. It may also be the
access method of choice, for example if we simply want to process a
sequence of data elements in order.
9. Random Access Files
Random access files consist of records that can be accessed in any sequence.
This means the data is stored exactly as it appears in memory, thus saving
processing time (because no translation is necessary) both in when the file is
written and in when it is read.
In computer science, random access (sometimes called direct access) is the
ability to access an arbitrary element of a sequence in equal time.
10. Random-Access Files
• A program can start reading or writing a
random-access file at any place and read or
write any number of bytes at a time.
• “Random-access file” is an abstraction: any
file can be treated as a random-access file.
• You can open a random-access file both for
reading and writing at the same time.
11. Random-Access Files (cont’d)
• A binary file containing fixed-length data
records is suitable for random-access
treatment.
• A random-access file may be accompanied
by an “index” (either in the same or a
different file), which tells the address of each
record.
12. File Types
Text
File Binary
Stream
Random-Access
common use
possible, but
not as common
13. What You Will Learn
Create files
Write files
Read files
Update files
14. Random Access Files
A RandomAccessFile employs an internal pointer that points to the next
byte to read.
This pointer is zero-based and the first byte is indicated by index 0.
When first created, a RandomAccessFile points to the first byte.
You can change the pointer's position by invoking the different methods.
The skipBytes method moves the pointer by the specified number of
bytes.
If offset number of bytes would pass the end of file, the internal pointer
will only move to as much as the end of file.
16. "r". Open for reading only.
"rw“. Open for reading and writing.
If the file does not already exist, Random Access
File creates the file.
"rws". Open for reading and writing and require that every
update to the file's content and metadata be written
synchronously.
"rwd". Open for reading and writing and require that every
update to the file's content (but not metadata) be
written synchronously.
20. Create File Q1.cpp
#include <fstream>
#include <iostream>
using namespace std;
void main( )
{
ofstream Savefile("D:Rose.txt");
Savefile<< "Sajid Ali Gillal";
}
May 21, 2010 Sajid Ali Gillal 20
21. File output with strings or lines of output P4.cpp
#include <fstream.h>
void main( )
{
ofstream outfile("E:Rose.txt");
outfile << "This is first line of Gillal Programn";
outfile << "This is second line of Gillal Programn";
outfile << "This is third line of Gillal Programn";
}
May 21, 2010 Sajid Ali Gillal 21
22. File input with characters P2.cpp
#include <fstream>
#include <iostream>
using namespace std;
void main( )
{
char ch;
ifstream Readfile("D:Rose.txt");
while(Readfile)
{
Readfile.get(ch);
cout << ch;
}
cout << endl;
}
May 21, 2010 Sajid Ali Gillal 22
23. file output with characters P5.cpp
#include <fstream>
#include <iostream>
#include <string>
using namespace std;
void main( )
{
string str = "If you start judging the people then
you will have no time to love them!";
ofstream Savefile("E:Rose.txt");
Savefile<<str;
cout << "File writtenn";
}
May 21, 2010 Sajid Ali Gillal 23
24. Reads person (full object) from disk P6.cpp
#include <fstream.h> void main( )
#include <iostream.h> {
#include <stdio.h>
#include <conio.h> person pers; //create person variable
FILE *ptr;
class person ptr = fopen("E:data2.txt","w");
{ fread(&pers,sizeof(pers),1,ptr);
protected: pers.showData();
char name[80]; //person's name getch();
short age; //person's age
}
public:
void showData( ) //display person's data
{
cout << "Name: " << name << endl;
cout << "Age: " << age << endl;
}
};
May 21, 2010 Sajid Ali Gillal 24
25. Save person (full object) to disk P7.cpp
#include <fstream.h> void main( )
#include <iostream.h> {
#include <stdio.h> person pers; //create a person
pers.getData(); //get data for person
class person
{ FILE *ptr;
protected: ptr = fopen("E:Rose.dat","wb");
char name[80]; //person's name fwrite(&pers,sizeof(pers),1,ptr);
short age; //person's age fclose(ptr);
public: }
void getData() //get person's data
{
cout << "Enter name: ";
cin >> name;
cout << "Enter age: ";
cin >> age;
}
};
May 21, 2010 Sajid Ali Gillal 25
26. OOP
Object Oriented Programming
Sajid Ali Gillal
May 21, 2010 Sajid Ali Gillal 26
