Basic Istream Unget In C++

The basic_istream::unget method is employed to push back a character, decrementing the position by one character and enabling the character to be used again. Make sure to include the correct header file for this operation.

The purpose of employing the basic_istream::unget function is to send a character back to the stream, enabling its convenient handling at a subsequent point. This method shifts the position back by one character, effectively reinstating the character that was previously taken out.

Header File

It included the <iostream> header file.

Syntax:

It has the following syntax:

basic_istream& unget();

The basic_istream::unget function does not accept any parameters.

The method basicistream::unget returns the basicistream object as its return value.

The following programs explain std::basic_istream::unget:

Example:

Filename: Ungetting1.cpp

// Program to implement the use of basic_istream::unget() 

#include <bits/stdc++.h> 

using namespace std; 

// main

int main() 

{ 

	// decreasing the size of the string stream

	istringstream con("ProgrammingLanguage"); 

	char a = con.get(); 

	if (con.unget()) { 

		char be = con.get(); 

		cout << "We got: " << a << endl; 

		cout << "After the ungetting, the character is: "

			<< be << endl; 

	} 

	return 0; 

}

Output:

We got: P

After the ungetting, the character is: P

Example 2:

Filename: Ungetting2.cpp

// Program to implement the use of basic_istream::unget() 

#include <bits/stdc++.h> 

using namespace std; 

// main

int main() 

{ 

	// decreasing the size of the string stream

	istringstream con("Language"); 

	char a = con.get(); 

	if (con.unget()) { 

		char be = con.get(); 

		cout << "We got: " << a << endl; 

		cout << "After the ungetting, the character is: "

			<< be << endl; 

	} 

	return 0; 

}

Output:

We got: L

After the ungetting, the character is: L

Explanation:

• ✅ An istringstream object con is created with the string "Language" to set up an input string stream.
• ✅ A character variable a is assigned the value retrieved by calling con.get. If con.unget is true, the first character 'L' from the stream is read and stored in a. { ... }: This section demonstrates the process of moving back one character in the stream using unget. The unget function returns true if it successfully moves back the stream position by one character.

Within the if statement:

When

• ✅ char be = con.get; is executed after unget, it retrieves an element from the stream. It is expected to output the same element ('L') that was previously retrieved and then "unget" back into the stream.

Following this, the values of variables a and be are displayed on the terminal.