Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages

  
 
  

home | help 
std::basic_...f::pbackfail(3) C++ Standard Libarystd::basic_...f::pbackfail(3)

NAME
       std::basic_streambuf::pbackfail - std::basic_streambuf::pbackfail

Synopsis
	  protected:
	  virtual int_type pbackfail( int_type c = Traits::eof() );

	  This	function  can only be called if	any of the following condition
       is satisfied:

	    * gptr() is	null,
	    * gptr() ==	eback(), or
	    * traits::eq(traits::to_char_type(c), gptr()[-1]) returns false.

	  This function	is called by the public	functions sungetc() and	 sput-
       backc() (which, in
	  turn,	are called by basic_istream::unget and basic_istream::putback)
       when either:

	  1)  There  is	 no  putback  position in the get area (pbackfail() is
       called with no
	  arguments). In this situation, the purpose of	pbackfail() is to back
       up the get area
	  by one character, if the associated character	sequence  allows  this
       (e.g. a
	  file-backed  streambuf  may  reload the buffer from a	file, starting
       one character
	  earlier).
	  2) The caller	attempts to putback a different	character from the one
       retrieved
	  earlier (pbackfail() is called with the character that needs	to  be
       put back). In
	  this situation, the purpose of pbackfail() is	to place the character
       c into the get
	  area	at  the	 position just before basic_streambuf::gptr(), and, if
       possible, to
	  modify the associated	character sequence  to	reflect	 this  change.
       This may	involve
	  backing up the get area as in	the first variant.

	  The default base class version of this function does nothing and re-
       turns
	  Traits::eof()	 in all	situations. This function is overridden	by the
       derived classes:
	  basic_stringbuf::pbackfail,	basic_filebuf::pbackfail,   strstream-
       buf::pbackfail, and
	  is expected to be overridden by user-defined and third-party library
       stream classes.

Parameters
	  ch  -	character to put back or Traits::eof() if only back out	is re-
       quested

Return value
	  Traits::eof()	in case	of failure, some other value to	indicate  suc-
       cess. The base
	  class	version	always fails.

Example
	   This	section	is incomplete
	   Reason: no example

	  Defect reports

	  The following	behavior-changing defect reports were applied retroac-
       tively to
	  previously published C++ standards.

	    DR	    Applied    to		     Behavior	as   published
       Correct
										    be-
       havior
			    the		      calling		     condition
       corrected to
	  LWG	32   C++98	  'traits::eq(*gptr(),traits::to_char_type(c))
       match
			    returns false' did not match  the  description  of
       the
			    sputbackc()
       description

See also
		    backs out the input	sequence to unget a character, not af-
       fecting the
	  pbackfail associated file
	  [virtual]  (virtual  protected  member  function of std::basic_file-
       buf<CharT,Traits>)

	  pbackfail puts a character back into the input sequence
	  [virtual] (virtual protected member function of
		    std::basic_stringbuf<CharT,Traits,Allocator>)
	  pbackfail backs out the input	sequence to unget a character
	  [virtual] (virtual protected member function of std::strstreambuf)
	  sungetc   moves the next pointer in the input	sequence back by one
		    (public member function)
	  sputbackc puts one character back in the input sequence
		    (public member function)

Category:
	    * Todo no example

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

Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=std::streambuf::pbackfail&sektion=3&manpath=FreeBSD+Ports+15.1.quarterly>

home | help