std::default_delete

 

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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() = default;	(1)
template <class U> default_delete( const default_delete<U>& d );	(2)	(member only of generic default_delete template)
template<class U> default_delete( const default_delete<U[]>& d);	(3)	(since C++17) (member only the array default_delete specialization)

1) Constructs a std::default_delete object.

2) Constructs a 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*.

3) Constructs a 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

Exceptions

noexcept specification:  

noexcept

  

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 ptr 2) Defined as deleted	(until C++17)
1) Calls delete on ptr 2) 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.

Example

Run this code

#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

unique_ptr (C++11)

smart pointer with unique object ownership semantics (class template)