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    std::default_delete

    From cppreference.com
     
    C++
     
    Memory management library
    (exposition only*)
    Allocators
    Uninitialized memory algorithms
    Constrained uninitialized memory algorithms
    Memory resources
    Uninitialized storage (until C++20)
    (until C++20*)
    (until C++20*)
    (until C++20*)

    Garbage collector support (until C++23)
    (C++11)(until C++23)
    (C++11)(until C++23)
    (C++11)(until C++23)
    (C++11)(until C++23)
    (C++11)(until C++23)
    (C++11)(until C++23)
     
    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.

    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

    		 constructs a default_delete object
    (public member function) [edit]
    		deletes the object or array
    (public member function) [edit]

    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)
    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(*)[].

    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)
    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 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

    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::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) [edit]