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class template

<memory>

std::uses_allocator

template <class T, class Alloc> struct uses_allocator;

Uses allocator


Trait class that identifies whether T accepts an allocator convertible from Alloc.

It inherits from integral_constant as being either true_type or false_type, depending on whether

T accepts such allocator.

The unspecialized definition for this template inherits from true_type if

T::allocator_type exists and is_convertible<Alloc,T::allocator_type>::value is not false.

Classes that do not fill this requirement but still use an allocator shall specialize this template to derive from true_type if either:

  • the last argument of a constructor has type Alloc.
  • or, the first argument of a constructor has type allocator_arg_t and the second argument has type Alloc.

Template parameters

T
A type.
Alloc
An allocator type.

Member types

Inherited from integral_constant:
member typedefinition
value_typebool
typeeither true_type or false_type

Member constants

Inherited from integral_constant:
member constantdefinition
valueeither true or false

Member functions

Inherited from integral_constant:
operator bool
Returns value (public member function)

Example

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// uses_allocator example
#include <iostream>
#include <memory>
#include <vector>

int main() {
  typedef std::vector<int> Container;
  typedef std::allocator<int> Allocator;

  if (std::uses_allocator<Container,Allocator>::value) {
    Allocator alloc;
    Container foo (5,10,alloc);
    for (auto x:foo) std::cout << x << ' ';
  }
  std::cout << '\n';
  return 0;
}

Output:


See also

allocator_traits
Allocator traits (class template)