std::default_delete
| 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.
default_delete uses delete to deallocate memory for a single object.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 > default_delete( const default_delete<U>& d ) noexcept; |
(2) | (since C++11) (constexpr since C++23) |
| Array specializations |
||
| template< class U > default_delete( const default_delete<U[]>& d ) noexcept; |
(3) | (since C++11) (constexpr since C++23) |
std::default_delete object.std::default_delete<T> object from another std::default_delete object.U* is implicitly convertible to T*.std::default_delete<T[]> object from another std::default_delete<U[]> object.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 > void operator()( U* ptr ) const; |
(2) | (since C++11) (constexpr since C++23) |
U(*)[] is implicitly convertible to T(*)[].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
#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 rejected qualification conversions | accept |
See also
| (C++11) |
smart pointer with unique object ownership semantics (class template) |