basic_istream::putback() in C++ with Examples

The basic_istream::putback() used to put the character back in the input string. This function is present in the iostream header file. Below is the syntax for the same:

Header File:

#include<iostream>

Syntax:

basic_istream& putback (char_type ch);

Parameter:

• ch: It represents the character to be put into the input string back.

Return Value: The iostream::basic_istream::putback() return the basic_istream object.

Below are the programs to understand the implementation of std::basic_istream::putback() in a better way:

Program 1:

// C++ code for basic_istream::putback()
#include <bits/stdc++.h>

using namespace std;

int main()
{
    stringstream gfg1("GeeksforGeeks");
    gfg1.get();

    // putback A into the input string
    if (gfg1.putback('A'))
        cout << gfg1.rdbuf() << endl;

    istringstream gfg2("GeeksforGeeks");
    gfg2.get();

    if (gfg2.putback('A'))
        cout << gfg2.rdbuf() << endl;
    else
        cout << "putback is failed here\n";

    gfg2.clear();

    // Again putback G in the string
    if (gfg2.putback('G'))
        cout << gfg2.rdbuf() << endl;
}

Output:

AeeksforGeeks
putback is failed here
GeeksforGeeks

Program 2:

// C++ code for basic_istream::putback()
#include <bits/stdc++.h>

using namespace std;

int main()
{
    stringstream gfg1("GOOD");
    gfg1.get();

    // putback B into the input string
    if (gfg1.putback('B'))
        cout << gfg1.rdbuf() << endl;

    istringstream gfg2("GOOD");
    gfg2.get();

    if (gfg2.putback('B'))
        cout << gfg2.rdbuf() << endl;
    else
        cout << "putback is failed here\n";

    gfg2.clear();

    // Again putback G in the string
    if (gfg2.putback('G'))
        cout << gfg2.rdbuf() << endl;
}

Output:

BOOD
putback is failed here
GOOD

Reference: http://www.cplusplus.com/reference/istream/istream/putback/