std::shared_ptr::use_count

 

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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.

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).
• 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.

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

unique

checks whether the managed object is managed only by the current shared_ptr instance (public member function)