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std::get_deleter(3) C++ Standard Libary std::get_deleter(3)


std::get_deleter - std::get_deleter


Defined in header <memory>
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.


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.


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.


demonstrates that std::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


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

See also

constructor std::shared_ptr constructors
(public member function)
get_deleter returns the deleter that is used for destruction of the managed object
(public member function of std::unique_ptr<T,Deleter>)