C++ basic_ios Library - putback

Description

It is used to put character back.

Declaration

Following is the declaration for std::basic_istream::putback.

basic_istream& putback (char_type c);

Parameters

c − Character to be put back.

Return Value

Returns the basic_istream object (*this).

Exceptions

Basic guarantee − if an exception is thrown, the object is in a valid state.

Data races

Modifies the stream object.

Example

In below example for std::basic_istream::putback.

#include <iostream>     
#include <string>       

int main () {
   std::cout << "Please, enter a number or a word: ";
   char c = std::cin.get();

   if ( (c >= '0') && (c <= '9') ) {
      int n;
      std::cin.putback (c);
      std::cin >> n;
      std::cout << "You entered a number: " << n << '\n';
   } else {
      std::string str;
      std::cin.putback (c);
      getline (std::cin,str);
      std::cout << "You entered a word: " << str << '\n';
   }
   return 0;
}

The output should be like this −

Please, enter a number or a word: pocket
You entered a word: pocket