Why does std::remove not work with std::set?

问题

The following code:

#include <iostream>
#include <set>
#include <algorithm>

std::set<int> s;

int main()
{
    s.insert(1);
    s.insert(2);

    std::remove(s.begin(), s.end(), 1);
}

does not compile with gcc 4.7.2:

$ LANG=C g++ test.cpp
In file included from /usr/include/c++/4.7/algorithm:63:0,
             from test.cpp:3:
/usr/include/c++/4.7/bits/stl_algo.h: In instantiation of '_FIter std::remove(_FIter, _FIter, const _Tp&) [with _FIter = std::_Rb_tree_const_iterator<int>; _Tp = int]':
test.cpp:12:38:   required from here
/usr/include/c++/4.7/bits/stl_algo.h:1135:13: error: assignment of read-only location '__result.std::_Rb_tree_const_iterator<_Tp>::operator*<int>()'

So I went to the definition of fset::iterator and I've found this in gcc's implementation (file ../c++/4.7/bits/stl_set.h, from 125):

  // _GLIBCXX_RESOLVE_LIB_DEFECTS                                                                                                                                                             
  // DR 103. set::iterator is required to be modifiable,                                                                                                                                      
  // but this allows modification of keys.                                                                                                                                                    
  typedef typename _Rep_type::const_iterator            iterator;
  typedef typename _Rep_type::const_iterator            const_iterator;
  typedef typename _Rep_type::const_reverse_iterator    reverse_iterator;
  typedef typename _Rep_type::const_reverse_iterator const_reverse_iterator;
  typedef typename _Rep_type::size_type                 size_type;
  typedef typename _Rep_type::difference_type           difference_type;

Why are both definitions constant? Why does my (pretty simple) code not work?

回答1:

std::set is ordered container, while std::remove changes order of elements in container placing elements that should be removed to the end, thus it can't be used with ordered containers where elements order is defined by predicate. You need to use:

s.erase( 1);

To remove 1 from set.

来源：https://stackoverflow.com/questions/16257538/why-does-stdremove-not-work-with-stdset

标签

c++

gcc

stdset