std::get_deleter
Defined in header <memory>.
Declarations
template< class Deleter, class T >
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 std::shared_ptr deleter is independent of the shared_ptr's type
#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!