Custom allocator & default member

Question

Why isn't this code compiling ?

#include <cstdlib>
#include <list>

template < typename Type >
class Allocator {
public:
    using value_type = Type;
public:
    template < typename Other >
    struct rebind { using other = Allocator< Other >; };
public:
    Type * allocate( std::size_t n ) { return std::malloc( n ); }
    void deallocate( Type * p, std::size_t ) throw ( ) { std::free( p ); }
};

int main( void ) {
    std::list< void *, Allocator< void * > > list;
    return 0;
}

It seems to need pointer, reference, pointer_const & reference_const types. However, according to cppreference these members are all optionals. It seems like if the STL weren't using allocator_trait (I'm compiling with -std=c++11 so it should be good).

Any idea ?

[edit] On clang, errors are :

user@/tmp > clang++ -std=c++11 test.cc
In file included from test.cc:2:
In file included from /usr/lib/gcc/i686-pc-linux-gnu/4.7.1/../../../../include/c++/4.7.1/list:63:
/usr/lib/gcc/i686-pc-linux-gnu/4.7.1/../../../../include/c++/4.7.1/bits/stl_list.h:449:40: error: no type named 'pointer' in 'Allocator<void *>'
      typedef typename _Tp_alloc_type::pointer           pointer;
              ~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~
test.cc:17:46: note: in instantiation of template class 'std::list<void *, Allocator<void *> >' requested here
    std::list< void *, Allocator< void * > > list;
                                             ^
In file included from test.cc:2:
In file included from /usr/lib/gcc/i686-pc-linux-gnu/4.7.1/../../../../include/c++/4.7.1/list:63:
/usr/lib/gcc/i686-pc-linux-gnu/4.7.1/../../../../include/c++/4.7.1/bits/stl_list.h:450:40: error: no type named 'const_pointer' in 'Allocator<void *>'
      typedef typename _Tp_alloc_type::const_pointer     const_pointer;
              ~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~
/usr/lib/gcc/i686-pc-linux-gnu/4.7.1/../../../../include/c++/4.7.1/bits/stl_list.h:451:40: error: no type named 'reference' in 'Allocator<void *>'
      typedef typename _Tp_alloc_type::reference         reference;
              ~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~
/usr/lib/gcc/i686-pc-linux-gnu/4.7.1/../../../../include/c++/4.7.1/bits/stl_list.h:452:40: error: no type named 'const_reference' in 'Allocator<void *>'
      typedef typename _Tp_alloc_type::const_reference   const_reference;
              ~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~
4 errors generated.

@Nick I have updated my question with clang output (gcc is failing too) — Maël Nison
– Maël Nison, Commented Sep 20, 2012 at 15:44
Note that the c++11 support for basically all compilers is still experimental/incomplete. Therefore it might simply be an implementation bug (can't look up the relevant parts of the standard right now, so that is just a guess if those members are indeed optional) — Grizzly
– Grizzly, Commented Sep 20, 2012 at 15:44
Shouldn't it be Allocator<void> instead of Allocator<void*>? — Nikolai Fetissov
– Nikolai Fetissov, Commented Sep 20, 2012 at 15:48
A sample custom allocator is here : stackoverflow.com/a/8090161/415784 — Sarfaraz Nawaz
– Sarfaraz Nawaz, Commented Sep 20, 2012 at 15:50

Bill Lynch · Accepted Answer · 2012-10-09 18:51:45Z

2

This is a bug in GCC's C++ standard library.

When using a list, they are not properly wrapping access to the allocator through an allocator_traits.

However, they do implement vector correctly. This code would compile if you used std::vector instead of std::list.

answered Oct 9, 2012 at 18:51

Bill Lynch

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