Introduction to files management systems

Chapter Seven
File Operations (File Input/output)
Computer Programming
By Leweyehu Y.

Introduction
• A file is a collection of related data stored in a
particular area on the disk.
• Programs can be designed to perform read or
write operations on these files.
• This involves two kinds of data communication:
1. Data transfer between the console unit and the program
2. Data transfer between the program and a disk file.
By Leweyehu Y.

 A file can be defined by following class ifstream, ofstream,
fstream, all these are defined in fstream header file.
 If a file object is declared by ifstream class, then that object can
be used for reading from a file.
 If a file object is declared by ofstream class, then that object can
be used for writing onto a file.
 If a file object is declared by fstream class then, that object can
be used for both reading from and writing to a file
By Leweyehu Y.

 In C++, I/O system supplies an interface to the programmer that is independent of the actual
device (terminals, disks, tape drives) being accessed.
 This interface is known as stream.
 A stream is a sequence of bytes. It acts as either as a source from which the input data can be
obtained or as a destination to which the output data can be sent.
 The source stream that provides data to the program is called input stream and the destination
stream that receives output from the program is called the output stream.
 A program extracts the bytes from an input stream and inserts bytes into an output stream.
Input
Device
Output
Device
Program
Output stream
Input stream
Extraction from
input stream
Insertion into
output stream.
Figure: Data streams
Stream Classes and I/O operations
By Leweyehu Y.

 ios : General input/output stream class.
 Contains basic facilities that are used by all other input and output classes.
 Declares constants and functions that are necessary for handling formatted input
and output operations.
 istream(input stream): Inherits the properties of ios.
 Declares input functions such as get(), getline() and read().
 Contains overloaded extraction operator >>
 ostream(output stream): Inherits the properties of ios.
 Declares output functions such as put() and write(). Contains overloaded
insertion operator <<
 iostream(input/output stream): Inherits the properties of ios, istream and ostream
By Leweyehu Y.

Table File mode parameters
parameter Meaning
ios:: app Append to end-of-file
ios::ate Go to end-of-file on opening
ios::binary Binary file
ios::in open file for reading only
ios::nocreate Open fails if the file does not exist
ios::noreplace Open fails if the file already exists
ios::out Open file for writing only
ios::trunc Delete contents of the file if it exists
By Leweyehu Y.

File basic operation open file
#include <iostream>
#include <fstream>
using namespacestd;
int main () {
ofstream myfile;
myfile.open ("example.txt");
myfile << "Writing this to a file.n";
myfile.close();
return0;
}
By Leweyehu Y.

Writing this to a file
• This code creates a file called example.txt and
inserts a sentence into it in the same way we are
used to do with cout, but using the file stream
myfile instead.
Opening a file
• The first operation generally performed on an
object of one of these classes is to associate it to
a real file.
By Leweyehu Y.

This procedure is known as to open a file.
In order to open a file with a stream object we use its
member function open():
open (filename, mode);
ofstream myfile;
myfile.open ("example.txt", ios::out | ios::app | ios::binary);
By Leweyehu Y.

Example 1: Writing a single line to a file
#include <iostream>
#include <fstream>
using namespace std;
int main() {
ofstream outputFile("output.txt");
if (outputFile.is_open()) {
outputFile << "Hello, World!"; // Write a single line to the file
outputFile.close();
cout << "Data written to the file successfully." <<endl;
} else {
cout << "Failed to open the file." << endl;
}
return 0;}
By Leweyehu Y.

Example 2: Writing multiple lines to a file
#include <iostream>
#include <fstream>
int main() {
outputFile << "Line 1n";
outputFile.close();
cout << "Data written to the file successfully." << endl;
} else {
std::cout << "Failed to open the file." << endl;
}
return 0;
} By Leweyehu Y.

Example 3: Writing data from an array to a file
#include <iostream>
#include <fstream>
int main() {
int data[] = {10, 20, 30, 40, 50};
for (int i = 0; i < 5; ++i) {
outputFile << data[i] << " ";
}
outputFile.close();
} else {
}
return 0;} By Leweyehu Y.

A character can be written onto a file using the put()function.
• #include<fstream>
• int main()
• {
• char c;
• ofstream outfile;
• outfile.open(“c:test.txt”,ios::out);
• if(outfile.fail())
• {
• cerr<< “nError opening test.txt”;
• exit(1);
• }
• for(int i=1;i<=15;i++)
• {
• cout<< “nEnter a character : ”;
• cin>>c;
• outfile.put(c);
• }
• output.close();
• }//end main
By Leweyehu Y.

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().
• myfile.close();
• Once this member function is called, the stream
object can be used to open another file, and the
file is available again to be opened by other
processes. By Leweyehu Y.

• #include <iostream>
• #include <fstream>
• using namespacestd;
• int main () {
ofstream myfile ("example.txt");
if(myfile.is_open())
{
myfile << "This is a line.n";
myfile << "This is another line.n";
myfile.close();
}
else
cout << "Unable to open file";
return 0;
• }
By Leweyehu Y.

Reading a file
#include<iostream>
#include<fstream>
int main()
{
ifstream input;
char s;
input.open("kal.txt",ios::out|ios::in);
if(input.is_open())
{
input>>s;
cout<<s;
}
input.close();
}
By Leweyehu Y.

Reading the file line by line
#include <iostream>
#include <fstream>
#include <string>
int main() {
ifstream inputFile("input.txt");
if (inputFile.is_open()) {
string line;
while (getline(inputFile, line)) {
cout << line << std::endl;
}
inputFile.close();
} else {
}
return 0;}
By Leweyehu Y.

• #include <iostream>
• #include <fstream>
• #include <string>
• using namespacestd;
int main () {
string line;
ifstream myfile ("example.txt");
if(myfile.is_open())
{
while(! myfile.eof() )
{
getline (myfile,line);
cout << line << endl;
}
myfile.close();
}
elsecout << "Unable to open file";
return 0;
• }
By Leweyehu Y.

Types of files
To write data to a sequential file in C++, you can use the
std::ofstream class along with the stream insertion operator (<<). An
example that demonstrates how to write data to a sequential file:
int main() {
outputFile << "Hello, World!" << endl;
outputFile << 42 << endl;
outputFile << 3.14159 << endl;
outputFile.close();
} else {
}return 0;}
By Leweyehu Y.

Read data from a sequential file
To read data from a sequential file in C++, you can use the
std::ifstream class along with the extraction operator (>>).
Here's an example that demonstrates how to read data
from a sequential file:
By Leweyehu Y.

#include <string>
int main() {
ifstream inputFile("input.txt");
if (inputFile.is_open()) {
string line;
int number;
double value;
while (getline(inputFile, line)) {
std::cout << "Read line: " << line << endl;
}
inputFile.close();
cout << "Data read from the file successfully." << endl;
} else {
}
return 0;
}
By Leweyehu Y.

Opening Random_access file
By Leweyehu Y.

Writting random access
ofstream out;
out.open("zinash.txt",ios::out|ios::app|ios::binary);
if(out.fail())
{
cerr<<"file not openedn";
exit(1);
}
int x;
cout<<"enter the numbern";
cin>>x;
out.write((char*) &x,sizeof(x));
out.close();
cout<<"data has been saved”<<endl;
By Leweyehu Y.

Reading random-access
ifstream in;int x;
in.open("zinash.txt",ios::in|ios::app|ios::binary);
if(in.fail())
{
cerr<<"file not openedn";
exit(1);
}
while(in.read((char*) &x,sizeof(x)));
cout<<x<<endl;
in.close();
return 0;
}
By Leweyehu Y.

Introduction to files management systems

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