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std::default_delete - cppreference.com

template< class T > struct default_delete;

template< class T > struct default_delete<T[]>;

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.

constexpr default_delete() noexcept = default;

Primary template specializations

template< class U >
default_delete( const default_delete<U>& d ) noexcept;

Array specializations

template< class U >
default_delete( const default_delete<U[]>& d ) noexcept;

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(*)[].

The converting constructor template of std::default_delete makes possible the implicit conversion from std::unique_ptr<Derived> to std::unique_ptr<Base>.

Primary template specializations

void operator()( T* ptr ) const;

Array specializations

template< class U >
void operator()( U* ptr ) const;

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.

No exception guarantees.

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.

#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>());
}

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

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