std::unique_ptr<T,Deleter>::reset (3) - Linux Manuals

std::unique_ptr<T,Deleter>::reset: std::unique_ptr<T,Deleter>::reset

NAME

std::unique_ptr<T,Deleter>::reset - std::unique_ptr<T,Deleter>::reset

Synopsis

members of the primary template, unique_ptr<T>
void reset( pointer ptr = pointer() ) noexcept; (1)
members of the specialization unique_ptr<T[]>
void reset( pointer ptr = pointer() ) noexcept; (2) (until C++17)
template< class U > (until C++17)
void reset( U ) = delete;
template< class U > (3) (since C++17)
void reset( U ) noexcept;
void reset( std::nullptr_t p ) noexcept; (4) (until C++17)
void reset( std::nullptr_t p = nullptr ) noexcept; (since C++17)

Replaces the managed object.
1) Given current_ptr, the pointer that was managed by *this, performs the following actions, in this order:

  1. Saves a copy of the current pointer old_ptr = current_ptr
  2. Overwrites the current pointer with the argument current_ptr = ptr
  3. If the old pointer was non-empty, deletes the previously managed object if(old_ptr) get_deleter()(old_ptr).

2) Behaves the same as the reset member of the primary template.
3) In the specialization for dynamic arrays, std::unique_ptr<T[]>, this template member is provided to prevent using reset() with a pointer to derived (which would result in undefined behavior with arrays). (until C++17)
4) In the specialization for dynamic arrays, std::unique_ptr<T[]>, this overload is necessary to allow reset to nullptr (which would otherwise be prohibited by the template overload). Equivalent to reset(pointer())
3) Behaves the same as the reset member of the primary template, except that it will only participate in overload resolution if either

  1. U is the same type as pointer, or (since C++17)
  2. pointer is the same type as element_type* and U is a pointer type V* such that V(*)[] is convertible to element_type(*)[].

4) Equivalent to reset(pointer())

Parameters

ptr - pointer to a new object to manage

Return value

(none)

Notes

To replace the managed object while supplying a new deleter as well, move assignment operator may be used.
A test for self-reset, i.e. whether ptr points to an object already managed by *this, is not performed, except where provided as a compiler extension or as a debugging assert. Note that code such as p.reset(p.release()) does not involve self-reset, only code like p.reset(p.get()) does.

Example

// Run this code

  #include <iostream>
  #include <memory>

  struct Foo {
      Foo() { std::cout << "Foo...\n"; }
      ~Foo() { std::cout << "~Foo...\n"; }
  };

  struct D {
      void operator() (Foo* p) {
          std::cout << "Calling delete for Foo object... \n";
          delete p;
      }
  };

  int main()
  {
      std::cout << "Creating new Foo...\n";
      std::unique_ptr<Foo, D> up(new Foo(), D()); // up owns the Foo pointer (deleter D)

      std::cout << "Replace owned Foo with a new Foo...\n";
      up.reset(new Foo()); // calls deleter for the old one

      std::cout << "Release and delete the owned Foo...\n";
      up.reset(nullptr);
  }

Output:

  Creating new Foo...
  Foo...
  Replace owned Foo with a new Foo...
  Foo...
  Calling delete for Foo object...
  ~Foo...
  Release and delete the owned Foo...
  Calling delete for Foo object...
  ~Foo...