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std::basic_...buf::sungetc(3)  C++ Standard Libary std::basic_...buf::sungetc(3)

NAME
     std::basic_streambuf::sungetc - std::basic_streambuf::sungetc

Synopsis
	int_type sungetc();

	If  a  putback position is available in the get area (gptr() > eback()),
     then
	decrements the next pointer (gptr()) and returns the  character  it  now
     points to.

	If  a  putback position is not available, then calls pbackfail() to back
     up the input
	sequence if possible.

	The I/O stream function basic_istream::unget is implemented in terms  of
     this
	function.

Parameters
	(none)

Return value
	If  putback  position was available, returns the character that the next
     pointer is
	now	pointing      at,      converted      to      int_type	    with
     Traits::to_int_type(*gptr()). The next
	single-character input from this streambuf will return this character.

	If putback position was not available, returns what pbackfail() returns,
     which is
	Traits::eof() on failure.

Example
     // Run this code

      #include <iostream>
      #include <sstream>

      int main()
      {
	  std::stringstream s("abcdef"); // gptr() points to 'a'
	  char c1 = s.get(); // c = 'a', gptr() now points to 'b'
	  char c2 = s.rdbuf()->sungetc(); // same as s.unget(): gptr() points to
     'a' again
	  char c3 = s.get(); // c3 = 'a', gptr() now points to 'b'
	  char c4 = s.get(); // c4 = 'b', gptr() now points to 'c'
	  std::cout << c1 << c2 << c3 << c4 << '\n';

	  s.rdbuf()->sungetc();  // back to 'b'
	  s.rdbuf()->sungetc();  // back to 'a'
	  int  eof  =  s.rdbuf()->sungetc();   //  nothing to unget: pbackfail()
     fails
	  if (eof == EOF)
		  std::cout << "Nothing to unget after 'a'\n";
      }

Output:
      aaab
      Nothing to unget after 'a'

See also
	sputbackc puts one character back in the input sequence
		  (public member function)
	unget	  unextracts a character
		  (public member function of std::basic_istream<CharT,Traits>)

http://cppreference.com 	   2024.06.10	   std::basic_...buf::sungetc(3)
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