Std::get_deleter (3) Linux Manual Page

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!

std::get_deleter (3) Linux Manual Page