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Allocators are classes that define memory models to be used by some parts of the Standard Library, and most specifically, by STL containers.
This section describes the default allocator template allocator (lowercase). This is the allocator that all standard containers will use if their last (and optional) template parameter is not specified, and is the only predefined allocator in the standard library.
Technically, a memory model described by allocators might be specialized for each type of object to be allocated and even may store local data for each container they work with. Although this does not happen with the default allocator.
Reference
C library:
- <cassert> (assert.h)
- <cctype> (ctype.h)
- <cerrno> (errno.h)
-
<cfenv> (fenv.h)C++11
- <cfloat> (float.h)
-
<cinttypes> (inttypes.h)C++11
- <ciso646> (iso646.h)
- <climits> (limits.h)
- <clocale> (locale.h)
- <cmath> (math.h)
- <csetjmp> (setjmp.h)
- <csignal> (signal.h)
- <cstdarg> (stdarg.h)
-
<cstdbool> (stdbool.h)C++11
- <cstddef> (stddef.h)
-
<cstdint> (stdint.h)C++11
- <cstdio> (stdio.h)
- <cstdlib> (stdlib.h)
- <cstring> (string.h)
-
<ctgmath> (tgmath.h)C++11
- <ctime> (time.h)
-
<cuchar> (uchar.h)C++11
- <cwchar> (wchar.h)
- <cwctype> (wctype.h)
Containers:
-
<array>C++11
- <deque>
-
<forward_list>C++11
- <list>
- <map>
- <queue>
- <set>
- <stack>
-
<unordered_map>C++11
-
<unordered_set>C++11
- <vector>
-
Input/Output:
Multi-threading:
-
<atomic>C++11
-
<condition_variable>C++11
-
<future>C++11
-
<mutex>C++11
-
<thread>C++11
-
Other:
- <algorithm>
- <bitset>
-
<chrono>C++11
-
<codecvt>C++11
- <complex>
- <exception>
- <functional>
-
<initializer_list>C++11
- <iterator>
- <limits>
- <locale>
- <memory>
- <new>
- <numeric>
-
<random>C++11
-
<ratio>C++11
-
<regex>C++11
- <stdexcept>
- <string>
-
<system_error>C++11
-
<tuple>C++11
-
<type_traits>C++11
-
<typeindex>C++11
- <typeinfo>
- <utility>
- <valarray>
<memory>
classes
- allocator
-
allocator_arg_tC++11
-
allocator_traitsC++11
- auto_ptr
- auto_ptr_ref
-
bad_weak_ptrC++11
-
default_deleteC++11
-
enable_shared_from_thisC++11
-
owner_lessC++11
-
pointer_traitsC++11
- raw_storage_iterator
-
shared_ptrC++11
-
unique_ptrC++11
-
uses_allocatorC++11
-
weak_ptrC++11
enum classes
-
pointer_safetyC++11
-
functions
-
addressofC++11
-
alignC++11
-
allocate_sharedC++11
-
const_pointer_castC++11
-
declare_no_pointersC++11
-
declare_reachableC++11
-
dynamic_pointer_castC++11
-
get_deleterC++11
-
get_pointer_safetyC++11
- get_temporary_buffer
-
make_sharedC++11
- return_temporary_buffer
-
static_pointer_castC++11
-
undeclare_no_pointersC++11
-
undeclare_reachableC++11
- uninitialized_copy
-
uninitialized_copy_nC++11
- uninitialized_fill
- uninitialized_fill_n
-
objects
-
allocator_argC++11
-
class template
<memory>
std::allocator
template <class T> class allocator;
Default allocator
This section describes the default allocator template allocator (lowercase). This is the allocator that all standard containers will use if their last (and optional) template parameter is not specified, and is the only predefined allocator in the standard library.
Other allocators may be defined. Any class having the same members as this default allocator and following its minimum requirements can be used as an allocator with the standard containers.
Other allocators may be defined. Any class Alloc for which allocator_traits<Alloc> produces a valid instantiation with the appropriate members defined can be used as an allocator on standard containers (Alloc may or may not implement the functionality through member functions).
Except for its destructor, no member of the standard default allocator class template shall introduce data races. Calls to member functions that allocate or deallocate storage shall occur in a single total order, and each such deallocation shall happen before the next allocation (if any) in this order.
Except for its destructor, no member of the standard default allocator class template shall introduce data races. Calls to member functions that allocate or deallocate storage shall occur in a single total order, and each such deallocation shall happen before the next allocation (if any) in this order.
Technically, a memory model described by allocators might be specialized for each type of object to be allocated and even may store local data for each container they work with. Although this does not happen with the default allocator.
Template parameters
- T
- Type of the elements allocated by the object (aliased as member type value_type).
Member types
| member | definition in allocator | represents |
|---|---|---|
| value_type | T | Element type |
| pointer | T* | Pointer to element |
| reference | T& | Reference to element |
| const_pointer | const T* | Pointer to constant element |
| const_reference | const T& | Reference to constant element |
| size_type | size_t | Quantities of elements |
| difference_type | ptrdiff_t | Difference between two pointers |
| rebind<Type> | member class | Its member type other is the equivalent allocator type to allocate elements of type Type |
| member | definition in allocator | represents |
|---|---|---|
| value_type | T | Element type |
| pointer | T* | Pointer to element |
| reference | T& | Reference to element |
| const_pointer | const T* | Pointer to constant element |
| const_reference | const T& | Reference to constant element |
| size_type | size_t | Quantities of elements |
| difference_type | ptrdiff_t | Difference between two pointers |
| rebind<Type> | member class | Its member type other is the equivalent allocator type to allocate elements of type Type |
| propagate_on_container_move_assignment | true_type | Indicates that allocator shall propagate when the container is move-assigned |
Member functions
- (constructor)
- Construct allocator object (public member function)
- (destructor)
- Allocator destructor (public member function)
- address
- Return address (public member function)
- allocate
- Allocate block of storage (public member function)
- deallocate
- Release block of storage (public member function)
- max_size
- Maximum size possible to allocate (public member function)
- construct
- Construct an object (public member function)
- destroy
- Destroy an object (public member function)
Template specializations
Header<memory> provides a specialization of allocator for the void type, defined as: |
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Spotted an error? contact us