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.
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) | |
| template <class U> default_delete( const default_delete<U>& d ) noexcept; |
(2) | (member only of generic default_delete template) |
| template<class U> default_delete( const default_delete<U[]>& d) noexcept; |
(3) | (since C++17) (member only of the array default_delete specialization) |
std::default_delete object.std::default_delete object from another std::default_delete object. This constructor will only participate in overload resolution if U* is implicitly convertible to T*.std::default_delete<U[]> object from another std::default_delete<U[]> object. This constructor will only participate in overload resolution 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()
| void operator()(T* ptr) const; |
(1) | (as of C++17, no longer a member of the default_delete<T[]> template specialization) |
| template <class U> void operator()(U* ptr) const; |
(2) | (member only of default_delete<T[]> template specialization, but defined as deleted prior to C++17) |
|
1) Calls
delete (primary template) or delete[] (array specialization) on ptr2) Defined as deleted
|
(until C++17) |
|
1) Calls
delete on ptr2) Calls delete[] on ptr. This function will only participate in overload resolution if U(*)[] is implicitly convertible to T(*)[].
|
(since C++17) |
In any case, 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.
Example
#include <memory> #include <vector> #include <algorithm> 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[]> ()); } // the destructor calls delete[], ok { 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>()); }
See also
| (C++11) |
smart pointer with unique object ownership semantics (class template) |