快速笔记:std::shared_ptr

link

https://stackoverflow.com/questions/5913396/why-do-stdshared-ptrvoid-work

description

• shared_ptr 构造时保留了析构函数指针
• 理论上子类析构可以没有 virtual 关键字，但是不建议
• 因为C语言的习惯，还是觉得 std::shared_ptr<void> 不应是个好的选择

code

#include <memory>
#include <iostream>
#include <vector>

class test {
public:
  test() {
    std::cout << "Test created" << std::endl;
  }
  ~test() {
    std::cout << "Test destroyed" << std::endl;
  }
};

class sub_test : public test {
public:
  sub_test() {
    std::cout << "sub_test created" << std::endl;
  }
  ~sub_test() {
    std::cout << "sub_test destroyed" << std::endl;
  }
};

int main() {
  std::cout << "At begin of main.\ncreating std::vector<std::shared_ptr<void>>"
            << std::endl;
  std::vector<std::shared_ptr<void>> v;
  {
    std::cout << "Creating test" << std::endl;
    v.push_back( std::shared_ptr<test>( new test() ) );
    v.push_back( std::shared_ptr<test>( new sub_test() ) );
    std::cout << "Leaving scope" << std::endl;
  }

  std::cout << "-------------1" << std::endl;
  v.pop_back();  // sub_test pop out
  std::cout << "-------------2" << std::endl;
  v.pop_back();  // test pop out
  std::cout << "-------------3" << std::endl;

  std::cout << "Leaving main" << std::endl;
  return 0;
}

// output
At begin of main.
creating std::vector<std::shared_ptr<void>>
Creating test
Test created
Test created
sub_test created
Leaving scope
-------------1
sub_test destroyed
Test destroyed
-------------2
Test destroyed
-------------3
Leaving main