關(guān)于STL 中allocator的接口與實(shí)現(xiàn)，C++標(biāo)準(zhǔn)有比較清楚的定義：
http://en.wikipedia.org/wiki/Allocator_(C%2B%2B)
1. 在GNU C++中，STL allocator嚴(yán)格遵守C++的標(biāo)準(zhǔn)：
看一下的代碼：（定義在bits/allocator.h文件中）
1 namespace std
2 {
3 template<typename _Tp>
4 class allocator;
5
6 template<>
7 class allocator<void>
8 {
9 public:
10 typedef size_t size_type;
11 typedef ptrdiff_t difference_type;
12 typedef void* pointer;
13 typedef const void* const_pointer;
14 typedef void value_type;
15
16 template<typename _Tp1>
17 struct rebind
18 { typedef allocator<_Tp1> other; };
19 };
20
21 /**
22 * @brief The "standard" allocator, as per [20.4].
23 *
24 * (See @link Allocators allocators info @endlink for more.)
25 */
26 template<typename _Tp>
27 class allocator: public ___glibcxx_base_allocator<_Tp>
28 {
29 public:
30 typedef size_t size_type;
31 typedef ptrdiff_t difference_type;
32 typedef _Tp* pointer;
33 typedef const _Tp* const_pointer;
34 typedef _Tp& reference;
35 typedef const _Tp& const_reference;
36
37 typedef _Tp value_type;
38
39 template<typename _Tp1>
40 struct rebind
41 { typedef allocator<_Tp1> other; };
42
43 allocator() throw() { }
44
45 allocator(const allocator& a) throw()
46 : ___glibcxx_base_allocator<_Tp>(a) { }
47
48 template<typename _Tp1>
49 allocator(const allocator<_Tp1>&) throw() { }
50
51 ~allocator() throw() { }
52
53 // Inherit everything else.
54 };
55
56 template<typename _T1, typename _T2>
57 inline bool
58 operator==(const allocator<_T1>&, const allocator<_T2>&)
59 { return true; }
60
61 template<typename _T1, typename _T2>
62 inline bool
63 operator!=(const allocator<_T1>&, const allocator<_T2>&)
64 { return false; }
65
66 // Inhibit implicit instantiations for required instantiations,
67 // which are defined via explicit instantiations elsewhere.
68 // NB: This syntax is a GNU extension.
69 #if _GLIBCXX_EXTERN_TEMPLATE
70 extern template class allocator<char>;
71
72 extern template class allocator<wchar_t>;
73 #endif
74
75 // Undefine.
76 #undef ___glibcxx_base_allocator
77 } // namespace std
78
template ___glibcxx_base_allocator 定義在具體的平臺相關(guān)的頭文件中，例如i386-redhat-linux/bits/c++allocator.h:
可以看出GNU c++的allocator其實(shí)采用的是new/delete-based allocation.
1 namespace __gnu_cxx
2 {
3 /**
4 * @brief An allocator that uses global new, as per [20.4].
5 *
6 * This is precisely the allocator defined in the C++ Standard.
7 * - all allocation calls operator new
8 * - all deallocation calls operator delete
9 *
10 * (See @link Allocators allocators info @endlink for more.)
11 */
12 template<typename _Tp>
13 class new_allocator
14 {
15 public:
16 typedef size_t size_type;
17 typedef ptrdiff_t difference_type;
18 typedef _Tp* pointer;
19 typedef const _Tp* const_pointer;
20 typedef _Tp& reference;
21 typedef const _Tp& const_reference;
22 typedef _Tp value_type;
23
24 template<typename _Tp1>
25 struct rebind
26 { typedef new_allocator<_Tp1> other; };
27
28 new_allocator() throw() { }
29
30 new_allocator(const new_allocator&) throw() { }
31
32 template<typename _Tp1>
33 new_allocator(const new_allocator<_Tp1>&) throw() { }
34
35 ~new_allocator() throw() { }
36
37
38 pointer
39 address(reference __x) const { return &__x; }
40
41 const_pointer
42 address(const_reference __x) const { return &__x; }
43
44 // NB: __n is permitted to be 0. The C++ standard says nothing
45 // about what the return value is when __n == 0.
46 pointer
47 allocate(size_type __n, const void* = 0)
48 { return static_cast<_Tp*>(::operator new(__n * sizeof(_Tp))); }
49
50 // __p is not permitted to be a null pointer.
51 void
52 deallocate(pointer __p, size_type)
53 { ::operator delete(__p); }
54
55 size_type
56 max_size() const throw()
57 { return size_t(-1) / sizeof(_Tp); }
58
59 // _GLIBCXX_RESOLVE_LIB_DEFECTS
60 // 402. wrong new expression in [some_] allocator::construct
61 void
62 construct(pointer __p, const _Tp& __val)
63 { ::new(__p) _Tp(__val); }
64
65 void
66 destroy(pointer __p) { __p->~_Tp(); }
67 };
68
69 template<typename _Tp>
70 inline bool
71 operator==(const new_allocator<_Tp>&, const new_allocator<_Tp>&)
72 { return true; }
73
74
75 template<typename _Tp>
76 inline bool
77 operator!=(const new_allocator<_Tp>&, const new_allocator<_Tp>&)
78 { return false; }
79 } // namespace __gnu_cxx
80