c_cpp shared_ptr用法与地图中的引用计数

Posted 2021-05-14

#include <iostream>
#include <memory>
#include <unordered_map>

//example of using shared_ptr in C++

const std::shared_ptr<int> dummy;

int main() {
  
  std::unordered_map<int, std::shared_ptr<int>> items;
  
  std::shared_ptr<int> ip = std::make_shared<int>(8);
  std::cout << "Use count:" << ip.use_count() << "\n";
  std::shared_ptr<int> ip2 = ip;
  std::cout << "Use count:" << ip.use_count() << "\n";
  items.insert({3, ip});
  items.insert({4, ip});
  std::cout << "Use count:" << ip.use_count() << "\n";
  items.erase(3);
  std::cout << "Use count:" << ip.use_count() << "\n";
  items[4] = dummy;
  std::cout << "Use count:" << ip.use_count() << "\n";
}
/*
Use count:1
Use count:2
Use count:4
Use count:3
Use count:2
*/