std::allocator
STD：：分配器
| Defined in header | | |
|---|---|---|
| template< class T > struct allocator; | (1) | |
| template<> struct allocator<void>; | (2) | (deprecated in C++17) |
大std::allocatorAllocator如果没有提供用户指定的分配器，所有标准库容器都将使用.。默认分配器是无状态的，也就是说，给定分配器的所有实例都是可互换的，比较相等，并且可以释放由同一分配器类型的任何其他实例分配的内存。
专门化void缺少成员类型reference，，，const_reference，，，size_type和difference_type此专门化不声明任何成员函数。
| All custom allocators also must be stateless. | (until C++11) |
|---|---|
| Custom allocators may contain state. Each container or another allocator-aware object stores an instance of the supplied allocator and controls allocator replacement through std::allocator_traits. | (since C++11) |
| The default allocator satisfies allocator completeness requirements. | (since C++17) |
成员类型
| Type | Definition |
|---|---|
| value_type | T |
| pointer (deprecated in C++17) | T* |
| const_pointer (deprecated in C++17) | const T* |
| reference (deprecated in C++17) | T& |
| const_reference (deprecated in C++17) | const T& |
| size_type (deprecated in C++17) | std::size_t |
| difference_type (deprecated in C++17) | std::ptrdiff_t |
| propagate_on_container_move_assignment(C++14) | std::true_type |
| rebind (deprecated in C++17) | template< class U > struct rebind { typedef allocator<U> other; }; |
| is_always_equal(C++17) | std::true_type |
成员函数
| (constructor) | creates a new allocator instance (public member function) |
|---|---|
| (destructor) | destructs an allocator instance (public member function) |
| address (deprecated in C++17) | obtains the address of an object, even if operator& is overloaded (public member function) |
| allocate | allocates uninitialized storage (public member function) |
| deallocate | deallocates storage (public member function) |
| max_size (deprecated in C++17) | returns the largest supported allocation size (public member function) |
| construct (deprecated in C++17) | constructs an object in allocated storage (public member function) |
| destroy (deprecated in C++17) | destructs an object in allocated storage (public member function) |
非会员职能
| operator==operator!= | compares two allocator instances (public member function) |
|---|
注记
成员模板类rebind提供获取不同类型的分配器的方法。例如，
| std::list | (until C++11) |
|---|---|
| std::list<T, A> allocates nodes of some internal type Node<T>, using the allocator std::allocator_traits<A>::rebind_alloc<Node<T>>, which is implemented in terms of A::rebind<Node<T>>::other if A is an std::allocator | (since C++11) |
例
二次
#include <memory>
#include <iostream>
#include <string>
int main()
{
std::allocator<int> a1; // default allocator for ints
int* a = a1.allocate(10 // space for 10 ints
a[9] = 7;
std::cout << a[9] << '\n';
a1.deallocate(a, 10
// default allocator for strings
std::allocator<std::string> a2;
// same, but obtained by rebinding from the type of a1
decltype(a1)::rebind<std::string>::other a2_1;
// same, but obtained by rebinding from the type of a1 via allocator_traits
std::allocator_traits<decltype(a1)>::rebind_alloc<std::string> a2_2;
std::string* s = a2.allocate(2 // space for 2 strings
a2.construct(s, "foo"
a2.construct(s + 1, "bar"
std::cout << s[0] << ' ' << s[1] << '\n';
a2.destroy(s
a2.destroy(s + 1
a2.deallocate(s, 2
}
二次
产出：
二次
7
foo bar
二次
另见
| allocator_traits (C++11) | provides information about allocator types (class template) |
|---|---|
| scoped_allocator_adaptor (C++11) | implements multi-level allocator for multi-level containers (class template) |
| uses_allocator (C++11) | checks if the specified type supports uses-allocator construction (class template) |
© cppreference.com
在CreativeCommonsAttribution下授权-ShareAlike未移植许可v3.0。
