std::weak_ptr<T>::use_count

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std::weak_ptr

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weak_ptr::weak_ptr
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weak_ptr::use_count
weak_ptr::expired
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weak_ptr::owner_equal (C++26)
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swap(std::weak_ptr)
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atomic<std::weak_ptr> (C++20)
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long use_count()constnoexcept;		(since C++11)

Returns the number ofshared_ptr instances that share ownership of the managed object, or0 if the managed object has already been deleted, i.e.*this is empty.

[edit]Parameters

(none)

[edit]Return value

The number ofshared_ptr instances sharing the ownership of the managed object at the instant of the call.

[edit]Notes

The usage and behavior of this function are similar tostd::shared_ptr::use_count, but it returns a different count.

[edit]Example

Run this code

#include <iostream>#include <memory> std::weak_ptr<int> gwp; void observe_gwp(){std::cout<<"use_count(): "<< gwp.use_count()<<"\t id: ";if(auto sp= gwp.lock())std::cout<<*sp<<'\n';elsestd::cout<<"??\n";} void share_recursively(std::shared_ptr<int> sp,int depth){    observe_gwp();// : 2 3 4if(1< depth)        share_recursively(sp, depth-1);    observe_gwp();// : 4 3 2} int main(){    observe_gwp();{auto sp=std::make_shared<int>(42);        gwp= sp;        observe_gwp();// : 1        share_recursively(sp,3);// : 2 3 4 4 3 2        observe_gwp();// : 1}    observe_gwp();// : 0}

Output:

use_count(): 0   id: ??use_count(): 1   id: 42use_count(): 2   id: 42use_count(): 3   id: 42use_count(): 4   id: 42use_count(): 4   id: 42use_count(): 3   id: 42use_count(): 2   id: 42use_count(): 1   id: 42use_count(): 0   id: ??