C++ basic_ios Library - peek

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Description

It is used to peek next character.

Declaration

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

int_type peek();

Parameters

none

Return Value

Returns the next character in the input sequence, without extracting it: The character is left as the next character to be extracted from the stream.

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::peek.

#include <iostream>     
#include <string>       
#include <cctype>       

int main () {

   std::cout << "Please, enter a number or a word: ";
   std::cout.flush();    

   std::cin >> std::ws;  
   std::istream::int_type c;
   c = std::cin.peek();  

   if ( c == std::char_traits<char>::eof() )
   return 1;
   if ( std::isdigit(c) ) {
      int n;
      std::cin >> n;
      std::cout << "You entered the number: " << n << '\n';
   } else {
      std::string str;
      std::cin >> str;
      std::cout << "You entered the word: " << str << '\n';
   }

   return 0;
}

The output should be like this −

Please, enter a number or a word: foobar
You entered the word: foobar