Chapter4.pptx

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 Outline:
◦ concept of byte streams
◦ File access methods
◦ Opening and closing files
◦ Reading from files
◦ Write to files

 When a program runs, the data is in the memory, but when it ends or
the computer shuts down, it gets lost. To keep data permanently, we
need to write it in a file.
 A file is a collection of information, usually stored on a computer’s
disk. Information can be saved to files and then later reused.
 All files are assigned a name that is used for identification purposes
by the operating system and the user.
 We use file handling to store data permanently.
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 Text file: it is a file that stores information in ASCII
characters. in a text file each line of text is terminated with a
special character known as EOL(End of Line) character or
delimiter character.
 Binary file: it is a file that contains information in the same
format as it is held in memory. in a binary file, no delimiters
are used for a line.
 Binary files are faster and easier for programs to read and
write.
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 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: this type of file access lets you jump to any
location in the file. Write data to file
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 A stream is a general term used to name the flow of
data.
 streams act as an interface between files and programs.
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 File input stream: reads data from disk file to the program.
 File output stream: writes data to the disk from the program.
 The I/O system of C++ contains:
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ofstream It used to create files and write on files.
ifstream It used to read from files.
fsream Supports both ifstream and ofstream operations.

Step1:Declare a file name variable
Step 2: Associate the file name variable with the disk file name.
Step3:Open the file
Step4:Use the file
Step5:Close the file
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functions operation
open() To create a file.
close() To close an exsisting file.
get() Read a single character from file
put() Write a single character in file
read() Read data from file
write() Write data into file.
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I. Declare a file name variable
◦ ifstream input_filename_var; // input file
◦ ofstream output_filename_var; // output file
II. Associate the file name variable with the
disk file name and open it.
◦ input_filename_var.open(“pathname/filename”);
◦ output_filename_var.open(“pathname/filename”);
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 A file must be opened before you can read from it or write to it.
 Either ofstream or fstream object may be used to open a file for writing.
ifstream object is used to open a file for reading purpose only.
 The following are the different modes in which we can open a file.
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ios::in opens a text file for reading.
ios::out opens a text file for writing.
ios::app
opens a text file for appending. (appending means to add text
at the end).
ios::ate
opens a file for output and move the read/write control to the
end of the file.
ios::trunc truncates the content before opening a file, if file exists.
ifstream input_filename_var(pathname/filename, ios::in);
ofstream input_filename_var(pathname/filename, ios::out);

Writing to a File:
 You write information to a file from your program using 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.
◦ ofstream ofile1;
◦ ofile1 << x << y; // x and y are integers
◦ ofile2 << ch; // ch is a char
◦ ofile3 << “Hi there!” << endl; // literal string
◦ ofile4 << str; // str is a char*
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 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.
◦ ifstream infile1;
◦ ifile1 >> x >> y; // x and y are integers
◦ ifile2 >> ch; // ch is a char
◦ ch = ifile3.get(); // ch is a char
◦ ifile4.getline(buffer, buffer_size) // buffer is char*
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Reading from a File

IV. Close the file
 When a C++ program terminates it automatically flushes all the
streams, release all the allocated memory and close all the opened
files. But it is always a good practice that a programmer should
close all the opened files before program termination.
◦ input_filename_var.close();
◦ output_filename_var.close();
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#include <fstream>
#include <iostream>
using namespace std;
int main ()
{
char data[100];
// open a file in write mode.
ofstream outfile;
outfile.open("afile.dat");
cout << "Writing to the file" << endl;
cout << "Enter your name: ";
cin.getline(data, 100);
// write inputted data into the file.
outfile << data << endl;
cout << "Enter your age: ";
cin >> data;
cin.ignore();
// again write inputted data into the file.
outfile << data << endl;
// close the opened file.
outfile.close();
// open a file in read mode.
ifstream infile;
infile.open("afile.dat");
cout << "Reading from the file" << endl;
infile >> data;
// write the data at the screen.
cout << data << endl;
// again read the data from the file and
display it.
infile >> data;
cout << data << endl;
// close the opened file.
infile.close();
return 0;
}

Chapter4.pptx

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Chapter4.pptx