[英]Custom allocator & default member
Why isn't this code compiling ? 为什么这段代码没有编译?
#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. 它似乎需要指针,引用,pointer_const和reference_const类型。 However, according to cppreference these members are all optionals.
但是,根据cppreference,这些成员都是可选项。 It seems like if the STL weren't using allocator_trait (I'm compiling with -std=c++11 so it should be good).
似乎STL没有使用allocator_trait(我正在使用-std = c ++ 11进行编译,所以它应该是好的)。
Any idea ? 任何的想法 ?
[edit] On clang, errors are : [编辑]在clang上,错误是:
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.
This is a bug in GCC's C++ standard library. 这是GCC的C ++标准库中的一个错误。
When using a list, they are not properly wrapping access to the allocator through an allocator_traits. 使用列表时,它们没有通过allocator_traits正确地包装对分配器的访问。
However, they do implement vector correctly. 但是,它们确实正确地实现了向量。 This code would compile if you used
std::vector
instead of std::list
. 如果您使用
std::vector
而不是std::list
则会编译此代码。
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