std::default_delete(3)

NAME
std::default_delete - std::default_delete

Synopsis
   Defined in header <memory>
   template< class T > struct default_delete; (1) (since C++11)
   template< class T > struct default_delete<T[]>; (2) (since C++11)
   std::default_delete is the default destruction policy used by std::unique_ptr when
   no deleter is specified. Specializations of default_delete are empty classes on
   typical implementations, and used in the empty base class optimization.
   1) The non-specialized default_delete uses delete to deallocate memory for a single
   object.
   2) A partial specialization for array types that uses delete[] is also provided.

Member functions
   constructor constructs a default_delete object
                 (public member function)
   operator() deletes the object or array
                 (public member function) std::default_delete::default_delete
   constexpr default_delete() noexcept = default; (1)
   Primary template specializations
   template< class U > (2) (since C++11)
   default_delete( const default_delete<U>& d ) noexcept; (constexpr since C++23)
   Array specializations
   template< class U > (3) (since C++11)
   default_delete( const default_delete<U[]>& d ) noexcept; (constexpr since C++23)
   1) Constructs a std::default_delete object.
   2) Constructs a std::default_delete<T> object from another std::default_delete
   object.
   This overload participates in overload resolution only if U* is implicitly
   convertible to T*.
   3) Constructs a std::default_delete<T[]> object from another
   std::default_delete<U[]> object.
   This overload participates in overload resolution only if U(*)[] is implicitly
   convertible to T(*)[].

Parameters
   d - a deleter to copy from

Notes
   The converting constructor template of std::default_delete makes possible the
   implicit conversion from std::unique_ptr<Derived> to std::unique_ptr<Base>. std::default_delete::operator()
   Primary template specializations
   void operator()( T* ptr ) const; (1) (since C++11)
                        (constexpr since C++23)
   Array specializations
   template< class U > (2) (since C++11)
   void operator()( U* ptr ) const; (constexpr since C++23)
   1) Calls delete on ptr.
   2) Calls delete[] on ptr.
   This overload participates in overload resolution only if U(*)[] is implicitly
   convertible to T(*)[].
   If U is an incomplete type, the program is ill-formed.

Parameters
   ptr - an object or array to delete

Exceptions
   No exception guarantees.
   Invoking over Incomplete Types
   At the point in the code the operator() is called, the type must be complete. In
   some implementations a static_assert is used to make sure this is the case. The
   reason for this requirement is that calling delete on an incomplete type is
   undefined behavior in C++ if the complete class type has a nontrivial destructor or
   a deallocation function, as the compiler has no way of knowing whether such
   functions exist and must be invoked.

Notes
       Feature-test macro Value Std Feature
   __cpp_lib_constexpr_memory 202202L (C++23) constexpr constructor and operator()

Example
// Run this code
 #include <algorithm>
 #include <memory>
 #include <vector>
 int main()
 {
 // {
 // std::shared_ptr<int> shared_bad(new int[10]);
 // } // the destructor calls delete, undefined behavior
     {
         std::shared_ptr<int> shared_good(new int[10], std::default_delete<int[]>());
     } // OK: the destructor calls delete[]
     {
         std::unique_ptr<int> ptr(new int(5));
     } // unique_ptr<int> uses default_delete<int>
     {
         std::unique_ptr<int[]> ptr(new int[10]);
     } // unique_ptr<int[]> uses default_delete<int[]>
     // default_delete can be used anywhere a delete functor is needed
     std::vector<int*> v;
     for (int n = 0; n < 100; ++n)
         v.push_back(new int(n));
     std::for_each(v.begin(), v.end(), std::default_delete<int>());
 }
   Defect reports
   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.
      DR Applied to Behavior as published Correct behavior
   LWG 2118 C++11 member functions of the array specializations accept
                       rejected qualification conversions

See also
   unique_ptr smart pointer with unique object ownership semantics
   (C++11) (class template)