C++ Memory Library - allocator

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Description

It defines the memory models to be used by some parts of the Standard Library, and most specifically, by STL containers.

Declaration

Following is the declaration for std::allocator function.

template <class T> class allocator;

C++11

template <class T> class allocator;

Parameters

T − It contains information about types of elements.

Member types

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

Example

In below example explains about std::allocator function.

#include <memory>
#include <iostream>
#include <string>

int main() {
   std::allocator<int> a1;
   int* a = a1.allocate(10);

   a[9] = 7;

   std::cout << a[9] << '\n';

   a1.deallocate(a, 10);

   std::allocator<std::string> a2;

   decltype(a1)::rebind<std::string>::other a2_1;

   std::allocator_traits<decltype(a1)>::rebind_alloc<std::string> a2_2;

   std::string* s = a2.allocate(2);

   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);
}

Let us compile and run the above program, this will produce the following result −

7
foo bar