std::get_deleter (3) - Linux Manuals

std::get_deleter: std::get_deleter

NAME

std::get_deleter - std::get_deleter

Synopsis

template< class Deleter, class T > (since C++11)
Deleter* get_deleter( const std::shared_ptr<T>& p ) noexcept;

Access to the p's deleter. If the shared pointer p owns a deleter of type cv-unqualified Deleter (e.g. if it was created with one of the constructors that take a deleter as a parameter), then returns a pointer to the deleter. Otherwise, returns a null pointer.

Parameters

p - a shared pointer whose deleter needs to be accessed

Return value

A pointer to the owned deleter or nullptr. The returned pointer is valid at least as long as there remains at least one shared_ptr instance that owns it.

Notes

The returned pointer may outlive the last shared_ptr if, for example, std::weak_ptrs remain and the implementation doesn't destroy the deleter until the entire control block is destroyed.

Example

demonstrates that shared_ptr deleter is independent of the shared_ptr's type
// Run this code

  #include <iostream>
  #include <memory>

  struct Foo { int i; };
  void foo_deleter(Foo * p)
  {
      std::cout << "foo_deleter called!\n";
      delete p;
  }

  int main()
  {
      std::shared_ptr<int> aptr;

      {
          // create a shared_ptr that owns a Foo and a deleter
          auto foo_p = new Foo;
          std::shared_ptr<Foo> r(foo_p, foo_deleter);
          aptr = std::shared_ptr<int>(r, &r->i); // aliasing ctor
          // aptr is now pointing to an int, but managing the whole Foo
      } // r gets destroyed (deleter not called)

      // obtain pointer to the deleter:
      if(auto del_p = std::get_deleter<void(*)(Foo*)>(aptr))
      {
          std::cout << "shared_ptr<int> owns a deleter\n";
          if(*del_p == foo_deleter)
              std::cout << "...and it equals &foo_deleter\n";
      } else
          std::cout << "The deleter of shared_ptr<int> is null!\n";
  } // deleter called here

Output:

  shared_ptr<int> owns a deleter
  ...and it equals &foo_deleter
  foo_deleter called!