std::shared_ptr::use_count

std::shared_ptr::use_count

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

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

#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);
}

sp1.use_count() == 1
fun: sp.use_count() == 2

See also