Computer Programming II
Lecture 9
Files Processing
- We have been using the iostream standard library, which
provides cin and cout methods for reading from standard
input and writing to standard output respectively.
- In this lecture we will know how to read and write from a
file.
Files Processing
- A file is a collection of information, usually stored on a
computer’s disk. Information can be saved to files and
later retrieved.
- The two basic types of files are : text files and binary
files.
Files Processing
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.
Files Processing
C++ File I/O Classes :
There are 3 File I/O classes in C++ which are used for File
Input(Read) / Output (Write) operations :
• ifstream : It is used to read information from file.
• ofstream : It is used to create files and to write
information to file.
• fstream : It has the capabilities of both ofstream and
ifstream which means it can create files, write information
to file, and read information from file.
*To perform file processing in C++, header files <iostream>
and <fstream> must be included in your C++ source file.
Files Processing
Opening a file:
A file must be opened before you can read from it or write
to it. Either the ofstream or fstream object may be
used to open a file for writing and ifstream object is used
to open a file for reading purpose only.
Files Processing
- In order to open a file with a stream object we use its
member function open():
object_name.open (filename, mode);
- Where filename is representing the name of the file to be
opened, and mode is an optional parameter with a
combination of the following flags:
Files Processing
Files Processing
Writing a file :
While doing C++ programming, you write information to a
file from your program using the stream insertion
operator (<<) just as you use that operator to output
information to the screen. The only difference is that you
use an ofstream or fstream object instead of the cout
object.
Files Processing
Writing to a text file using fstream class:
Writing to a text file can be achieved with the stream
operators. This also follows the same order of operations,
though with a slight difference.
1. open a file – in write mode.
2. Write to a file.
3. close the file.
- This sample code snippet explains how to use the C++ file
i/o stream operators to write data from a file. In all cases
the header file fstream.h must be included.
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Files Processing
Reading from a file:
You read information from a file into your program using
the stream extraction operator (>>) just as you use that
operator to input information from the keyboard. The
only difference is that you use an ifstream or fstream
object instead of the cin object.
Files Processing
Reading a text file using (fstream) class:
There are several ways of reading the text from a file. But
all of them have a common approach as follows:
• Open the file
• Read the data
• Close the file
Look at the following sample code to see the difference.
Files Processing
Files Processing
Closing a file:
When we are finished with our input and output operations
on a file we shall close it so that its resources become
available again. In order to do that we have to call the
stream's member function close(). This member function
takes no parameters, and what it does is to flush the
associated buffers and close the file:
Object_name.close( );
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- Write a C++ program that used to:
1- Allow user to enter his\her name.
2- Create a text file with this name (myfile) on the disk
drive (D) and then save the user’s name inside it.
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Files Processing
Files Processing
- Write a C++ program that used to create a text file with
this name (student) on the disk drive (D) and then save
the data for 3 students inside it.
Note :
- The student data are : student number and student name.
- These data should inserted by user.
Files Processing
Files Processing
Files Processing
- Write a C++ program that used to allow you to enter the
student data and then it will add it to the previous text
file which named as (student) on the disk drive (D).
Note :
- The student data are : student number and student name.
Files Processing
Files Processing