In file included from c:\mingw\lib\gcc\mingw32\4.8.1\include\c++\algorithm:62:0,
                 from foo.cpp:3:
c:\mingw\lib\gcc\mingw32\4.8.1\include\c++\bits\stl_algo.h: In instantiation of '_RandomAccessIterator std::__unguarded_partition(_RandomAccessIterator, _RandomAccessIterator, const _Tp&) [with _RandomAccessIterator = aaa*; _Tp = aaa]':
c:\mingw\lib\gcc\mingw32\4.8.1\include\c++\bits\stl_algo.h:2307:70:   required from '_RandomAccessIterator std::__unguarded_partition_pivot(_RandomAccessIterator, _RandomAccessIterator) [with _RandomAccessIterator = aaa*]'
c:\mingw\lib\gcc\mingw32\4.8.1\include\c++\bits\stl_algo.h:2338:54:   required from 'void std::__introsort_loop(_RandomAccessIterator, _RandomAccessIterator, _Size) [with _RandomAccessIterator = aaa*; _Size = int]'
c:\mingw\lib\gcc\mingw32\4.8.1\include\c++\bits\stl_algo.h:5475:36:   required from 'void std::sort(_RAIter, _RAIter) [with _RAIter = aaa*]'
foo.cpp:82:14:   required from here
c:\mingw\lib\gcc\mingw32\4.8.1\include\c++\bits\stl_algo.h:2269:19: error: passing 'const aaa' as 'this' argument of 'bool aaa::operator<(aaa)' discards qualifiers [-fpermissive]
    while (__pivot < *__last)
                   ^