- Example

// weakPtr.cpp
#include <iostream>
#include <memory>
int main(){
  std::cout << std::boolalpha << std::endl;
  auto sharedPtr=std::make_shared<int>(2011);
  std::weak_ptr<int> weakPtr(sharedPtr);
  
  std::cout << "weakPtr.use_count(): " << weakPtr.use_count() << std::endl;
  std::cout << "sharedPtr.use_count(): " << sharedPtr.use_count() << std::endl;
  std::cout << "weakPtr.expired(): " << weakPtr.expired() << std::endl;
  if( std::shared_ptr<int> sharedPtr1 = weakPtr.lock() ) {
    std::cout << "*sharedPtr: " << *sharedPtr << std::endl;
    std::cout << "sharedPtr1.use_count(): " << sharedPtr1.use_count() << std::endl;
  }
  else{
    std::cout << "Don't get the resource!" << std::endl;
  }
  weakPtr.reset();
  if( std::shared_ptr<int> sharedPtr1 = weakPtr.lock() ) {
    std::cout << "*sharedPtr: " << *sharedPtr << std::endl;
    std::cout << "sharedPtr1.use_count(): " << sharedPtr1.use_count() << std::endl;
  }
  else{
    std::cout << "Don't get the resource!" << std::endl;
  }
  std::cout << std::endl;
}