c++ - Cpp线程对象和shared_ptr问题

当我在此处阅读cppreference中的文档时
https://en.cppreference.com/w/cpp/memory/shared_ptr#Example
我想知道打印出的第一个lp.use_count()的可能值是什么？我在输出内容中将其标记为“<<<<<#include <iostream>#include <memory>#include <thread>#include <chrono>#include <mutex>struct Base{ Base() { std::cout << " Base::Base()\n"; } // Note: non-virtual destructor is OK here ~Base() { std::cout << " Base::~Base()\n"; }};struct Derived: public Base{ Derived() { std::cout << " Derived::Derived()\n"; } ~Derived() { std::cout << " Derived::~Derived()\n"; }};void thr(std::shared_ptr<Base> p){ std::this_thread::sleep_for(std::chrono::seconds(1)); std::shared_ptr<Base> lp = p; // thread-safe, even though the // shared use_count is incremented { static std::mutex io_mutex; std::lock_guard<std::mutex> lk(io_mutex); std::cout << "local pointer in a thread:\n" << " lp.get() = " << lp.get() << ", lp.use_count() = " << lp.use_count() << '\n'; }}int main(){ std::shared_ptr<Base> p = std::make_shared<Derived>(); std::cout << "Created a shared Derived (as a pointer to Base)\n" << " p.get() = " << p.get() << ", p.use_count() = " << p.use_count() << '\n'; std::thread t1(thr, p), t2(thr, p), t3(thr, p); p.reset(); // release ownership from main std::cout << "Shared ownership between 3 threads and released\n" << "ownership from main:\n" << " p.get() = " << p.get() << ", p.use_count() = " << p.use_count() << '\n'; t1.join(); t2.join(); t3.join(); std::cout << "All threads completed, the last one deleted Derived\n";}

Possible output:

Base::Base()
  Derived::Derived()
Created a shared Derived (as a pointer to Base)
  p.get() = 0x2299b30, p.use_count() = 1
Shared ownership between 3 threads and released
ownership from main:
  p.get() = 0, p.use_count() = 0
local pointer in a thread:
  lp.get() = 0x2299b30, lp.use_count() = 5   <<<<<<<< HERE <<<<<<
local pointer in a thread:
  lp.get() = 0x2299b30, lp.use_count() = 3
local pointer in a thread:
  lp.get() = 0x2299b30, lp.use_count() = 2
  Derived::~Derived()
  Base::~Base()
All threads completed, the last one deleted Derived

@ user2452809的回答非常受赞赏，指出了use_count()的重要功能。
假设use_count()将返回准确的计数，答案是什么？

最佳答案

无论如何，我不会依赖于这一值(value)。

检查引用以获取更多信息:https://en.cppreference.com/w/cpp/memory/shared_ptr/use_count