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std::default_delete(3) C++ Standard Libary 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 optimiza- tion. 1) The non-specialized default_delete uses delete to deallocate mem- ory 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; (const- expr since C++23) Array specializations template< class U > (3) (since C++11) default_delete( const default_delete<U[]>& d ) noexcept; (const- expr since C++23) 1) Constructs a std::default_delete object. 2) Constructs a std::default_delete<T> object from another std::de- fault_delete object. This overload participates in overload resolution only if U* is im- plicitly 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 nontriv- ial 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::de- fault_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 retroac- tively 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) http://cppreference.com 2024.06.10 std::default_delete(3)
NAME | Synopsis | Member functions | Parameters | Notes | Parameters | Exceptions | Notes | Example | See also
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