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std::basic_istream::seekg(3)  C++ Standard Libary std::basic_istream::seekg(3)

NAME
       std::basic_istream::seekg - std::basic_istream::seekg

Synopsis
	  basic_istream&	 seekg(		pos_type	 pos	    );
       (1)
	  basic_istream& seekg(	off_type off,  std::ios_base::seekdir  dir  );
       (2)

	  Sets	input  position	 indicator of the current associated streambuf
       object.

	  Before doing anything	else, seekg clears eofbit. (since C++11)

	  seekg	behaves	as UnformattedInputFunction, except that  gcount()  is
       not affected.
	  After	constructing and checking the sentry object,

	  1)  if fail()	!= true, sets the input	position indicator to absolute
       (relative to the
	  beginning  of	 the  file)  value  pos.  Specifically,	 executes  rd-
       buf()->pubseekpos(pos,
	  std::ios_base::in)  (pubseekpos,  in turn, calls seekpos of the spe-
       cific buffer, such
	  as basic_filebuf::seekpos, basic_stringbuf::seekpos,	or  strstream-
       buf::seekpos). In
	  case of failure, calls setstate(std::ios_base::failbit).
	  2)  if fail()	!= true, sets the input	position indicator to position
       off, relative to
	  position,  defined  by  dir.	Specifically,  executes	 rdbuf()->pub-
       seekoff(off, dir,
	  std::ios_base::in).	 In    case    of    failure,	 calls	  set-
       state(std::ios_base::failbit).

Parameters
	  pos -	absolute position to set the input position indicator to
	  off -	relative position (positive or negative) to set	the input  po-
       sition indicator
		to
		defines	 base position to apply	the relative offset to.	It can
       be one of the
		following constants:

	  dir -	Constant Explanation
		beg	 the beginning of a stream
		end	 the ending of a stream
		cur	 the current position of stream	position indicator

Return value
	  *this

Exceptions
	  failure if an	error occurred (the error state	flag is	 not  goodbit)
       and exceptions()
	  is set to throw for that state.

	  If  an internal operation throws an exception, it is caught and bad-
       bit is set. If
	  exceptions() is set for badbit, the exception	is rethrown.

Notes
	  seekg(n)  is	not  necessarily  equivalent  to  seekg(n,  ios::beg).
       std::basic_ifstream,
	  for example, requires	the absolute position n	to come	from tellg().

Example
       // Run this code

	#include <iostream>
	#include <sstream>
	#include <string>

	int main()
	{
	    std::string	str = "Hello, world";
	    std::istringstream in(str);
	    std::string	word1, word2;

	    in >> word1;
	    in.seekg(0); // rewind
	    in >> word2;

	    std::cout << "word1	= " << word1 <<	'\n'
		      << "word2	= " << word2 <<	'\n';
	}

Output:
	word1 =	Hello,
	word2 =	Hello,

	  Defect reports

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

	    DR	   Applied to	      Behavior as published		  Cor-
       rect behavior
	  LWG 129 C++98	     there was no way to indicate a failure sets fail-
       bit on failure
	  LWG 136 C++98	     seekg could set the output	stream	    only  sets
       the input stream
	  LWG  537 C++98      the type of off was off_type&	     corrected
       to off_type

See also
	  tellg	     returns the input position	indicator
		     (public member function)
	  tellp	     returns the output	position indicator
		     (public	 member	    function	 of	std::basic_os-
       tream<CharT,Traits>)
	  seekp	     sets the output position indicator
		     (public	 member	    function	 of	std::basic_os-
       tream<CharT,Traits>)
	  pubseekpos invokes seekpos()
		     (public	member	  function    of    std::basic_stream-
       buf<CharT,Traits>)
	  seekpos    repositions the file position, using absolute addressing
	  [virtual]   (virtual	protected  member function of std::basic_file-
       buf<CharT,Traits>)

		     repositions the next pointer in the input sequence,  out-
       put sequence, or
	  seekpos    both using	absolute addressing
	  [virtual]  (virtual protected	member function	of
		     std::basic_stringbuf<CharT,Traits,Allocator>)
	  seekpos     repositions the next pointer in the input	sequence, out-
       put sequence, or
	  [virtual]  both using	absolute addressing
		     (virtual protected	member function	of std::strstreambuf)
	  pubseekoff invokes seekoff()
		     (public	member	  function    of    std::basic_stream-
       buf<CharT,Traits>)
	  seekoff    repositions the file position, using relative addressing
	  [virtual]   (virtual	protected  member function of std::basic_file-
       buf<CharT,Traits>)

		     repositions the next pointer in the input sequence,  out-
       put sequence, or
	  seekoff    both, using relative addressing
	  [virtual]  (virtual protected	member function	of
		     std::basic_stringbuf<CharT,Traits,Allocator>)
	  seekoff     repositions the next pointer in the input	sequence, out-
       put sequence, or
	  [virtual]  both, using relative addressing
		     (virtual protected	member function	of std::strstreambuf)

http://cppreference.com		  2024.06.10	  std::basic_istream::seekg(3)

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