std::shared_ptr::use_count
From cppreference.com
< cpp | memory | shared ptr
long use_count() const; |
||
Returns the number of different shared_ptr
instances (this included) managing the current object. If there is no managed object, 0 is returned.
In multithreaded environment, the value returned by use_count is approximate (typical implementations use a memory_order_relaxed load)
Parameters
(none)
Return value
the number of shared_ptr
instances managing the current object or 0 if there is no managed object.
Exceptions
noexcept specification:
noexcept
Notes
Common use cases include
- comparison with 0. If
use_count
returns zero, the shared pointer is empty and manages no objects (whether or not its stored pointer is null). However, this is not guaranteed in multithreaded environment. - comparison with 1. If
use_count
returns 1, there are no other owners, which may indicate that the managed object is safe to modify. The member function unique() is provided for this use case. However, this is not guaranteed in multithreaded environment.
Example
Run this code
#include <memory> #include <iostream> void fun(std::shared_ptr<int> sp) { std::cout << "fun: sp.use_count() == " << sp.use_count() << '\n'; } int main() { auto sp1 = std::make_shared<int>(5); std::cout << "sp1.use_count() == " << sp1.use_count() << '\n'; fun(sp1); }
Output:
sp1.use_count() == 1 fun: sp.use_count() == 2
See also
(deprecated) |
checks whether the managed object is managed only by the current shared_ptr instance (public member function) |