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std::basic_...f::sputbackc(3)  C++ Standard Libary std::basic_...f::sputbackc(3)

NAME
     std::basic_streambuf::sputbackc - std::basic_streambuf::sputbackc

Synopsis
	int_type sputbackc( char_type c );

	Puts back a character back to the get area.

	If  a  putback position is available in the get area (gptr() > eback()),
     and the
	character c is equal to the character one position to the left of gptr()
     (as
	determined by Traits::eq(c, gptr()[-1]), then simply decrements the next
     pointer
	(gptr()).

	Otherwise, calls pbackfail(Traits::to_int_type(c)) to either back up the
     get area or
	to modify both the get area and possibly the  associated  character  se-
     quence.

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

Parameters
	c - character to put back

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' in "abcdef"
	  std::cout << "Before putback, string holds " << s.str() << '\n';
	  char c1 = s.get(); // c1 = 'a', gptr() now points to 'b' in "abcdef"
	  char c2 = s.rdbuf()->sputbackc('z'); // same as s.putback('z')
					       // gptr() now points  to  'z'  in
     "zbcdef"
	  std::cout << "After putback, string holds " << s.str() << '\n';
	  char c3 = s.get(); // c3 = 'z', gptr() now points to 'b' in "zbcdef"
	  char c4 = s.get(); // c4 = 'b', gptr() now points to 'c' in "zbcdef"
	  std::cout << c1 << c2 << c3 << c4 << '\n';

	  s.rdbuf()->sputbackc('b');  // gptr() now points to 'b' in "zbcdef"
	  s.rdbuf()->sputbackc('z');  // gptr() now points to 'z' in "zbcdef"
	  int eof = s.rdbuf()->sputbackc('x');	// nothing to unget: pbackfail()
     fails
	  if (eof == EOF)
	      std::cout << "No room to putback after 'z'\n";
      }

Output:
      Before putback, string holds abcdef
      After putback, string holds zbcdef
      azzb
      No room to putback after 'z'

See also
	sungetc moves the next pointer in the input sequence back by one
		(public member function)
	putback puts a character into input stream
		(public member function of std::basic_istream<CharT,Traits>)

http://cppreference.com 	   2024.06.10	   std::basic_...f::sputbackc(3)
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