std::shared_ptr::use_count

`long use_count() const noexcept;`

shared_ptr ( this), . , 0.

, use_count, ( memory_order_relaxed)

()

std::shared_ptr, , 0, .

0. use_count , ( , nullptr).
1. use_count 1, . ( C++17) - unique(). ( C++20) , , , , , std::weak_ptr::lock.

#include <memory>
#include <iostream>

void fun(std::shared_ptr<int> sp)
{
    std::cout << " fun(): sp.use_count() == " << sp.use_count()
              << " ( @ " << sp << ")\n";
}

int main()
{
    auto sp1 = std::make_shared<int>(5);
    std::cout << " main(): sp1.use_count() == " << sp1.use_count()
              << " ( @ " << sp1 << ")\n";

    fun(sp1);
}

:

 main(): sp1.use_count() == 1 ( @ 0x20eec30)
 fun(): sp.use_count() == 2 ( @ 0x20eec30)

unique

( C++20)

, shared_ptr
(public -) []







(C++20)

(C++20)
(C++11)





(C++20)


/

(C++11)
(C++11)
(C++11)
(C++17)

-
shared_ptr::shared_ptr
shared_ptr::~shared_ptr
shared_ptr::operator=

shared_ptr::reset
shared_ptr::swap

shared_ptr::get
shared_ptr::operator*shared_ptr::operator->
shared_ptr::operator[] (C++17)
shared_ptr::use_count
shared_ptr::unique ( C++20*)
shared_ptr::operator bool
shared_ptr::owner_before
,
std::swap
make_sharedmake_shared_for_overwrite (C++20)
allocate_sharedallocate_shared_for_overwrite (C++20)
static_pointer_castdynamic_pointer_castconst_pointer_castreinterpret_pointer_cast (C++17)
get_deleter
operator==operator!=operator<operator<=operator>operator>=operator<=> ( C++20)( C++20)( C++20)( C++20)( C++20)(C++20)
operator<<
atomic_xxx functions ( C++20)
std::atomic<std::shared_ptr> (C++20)
std::hash
(C++17)

cppreference.com

std::shared_ptr::use_count