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

	  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  charac-
       ter.

	  If  putback position was not available, returns what pbackfail() re-
       turns, 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:	pback-
       fail() 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 character into input stream
		  (public member function of std::basic_istream<CharT,Traits>)

http://cppreference.com		  2022.07.31	 std::basic_...f::sputbackc(3)

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