Re: libstdc++/8195: n-th algorithm (STL) doesn`t work properly

["Belov, Eugeny" <Eugeny_Belov@stl.sarov.ru>]

The following reply was made to PR libstdc++/8195; it has been noted by GNATS.

From: "Belov, Eugeny" <Eugeny_Belov@stl.sarov.ru>
To: Wolfgang Bangerth <bangerth@ticam.utexas.edu>
Cc: gcc-bugs@gcc.gnu.org, gcc-gnats@gcc.gnu.org
Subject: Re: libstdc++/8195: n-th algorithm (STL) doesn`t work properly
Date: Fri, 11 Oct 2002 19:42:01 +0400

     Hello Wolfgang
 
   I am understanding that the principle of this algorithm (in simple 
 terms) is to divide the sequence into 2 parts like this:
 smaller elements , n-th element, bigger elements,  and in the general 
 case both parts can be unsorted.
   But the real problem in this case is that smaller elements comes after 
 n-th ("n-th" is the integer with value 12 - the biggiest of all other 
 elements), i.e. the sequence after using the nth_element() is "4 4 5 6 6 
 6 9 _12_ 8 10" and in this case I think the n-th algorithm 
 implementation make a mistake.
 
 With best regards.
 Eugeny.
 
 
 Wolfgang Bangerth wrote:
 
 >This is not a bug, so may be closed.
 >
 >nth_element does not sort the _entire_ array, it only makes sure that the 
 >elements before the nth-pointer are smaller, and the ones behind that are 
 >larger than the element pointed to by nth (the second argument). It makes 
 >no guarantees that each of these two parts of the entire range is sorted 
 >itself.
 >
 >Regards
 >  Wolfgang
 >
 >-------------------------------------------------------------------------
 >Wolfgang Bangerth              email:           bangerth@ticam.utexas.edu
 >                               www: http://www.ticam.utexas.edu/~bangerth
 >