std::allocator

#include <iostream>
#include <memory>
#include <string>
 
int main()
{
 // default allocator for ints
 std::allocator<int> alloc1;
 
 // demonstrating the few directly usable members
 static_assert(std::is_same_v <int, decltype(alloc1)::value_type>);
 int* p1 = alloc1.allocate(1); // space for one int
 alloc1.deallocate(p1, 1); // and it is gone
 
 // Even those can be used through traits though, so no need
 using traits_t1 = std::allocator_traits <decltype(alloc1)>; // The matching trait
 p1 = traits_t1::allocate(alloc1, 1);
 traits_t1::construct(alloc1, p1, 7); // construct the int
 std::cout << *p1 << '\n';
 traits_t1::deallocate(alloc1, p1, 1); // deallocate space for one int
 
 // default allocator for strings
 std::allocator<std::string > alloc2;
 // matching traits
 using traits_t2 = std::allocator_traits <decltype(alloc2)>;
 
 // Rebinding the allocator using the trait for strings gets the same type
 traits_t2::rebind_alloc<std::string > alloc_ = alloc2;
 
 std::string * p2 = traits_t2::allocate(alloc2, 2); // space for 2 strings
 
 traits_t2::construct(alloc2, p2, "foo");
 traits_t2::construct(alloc2, p2 + 1, "bar");
 
 std::cout << p2[0] << ' ' << p2[1] << '\n';
 
 traits_t2::destroy(alloc2, p2 + 1);
 traits_t2::destroy(alloc2, p2);
 traits_t2::deallocate(alloc2, p2, 2);
}

7
foo bar