5.1.shared.ptr.a.cpp

//
// 5.1.shared.ptr.cpp
// chapter 05 start pointers and memory management
// modern c++ tutorial
//
// created by changkun at changkun.de
// https://github.com/changkun/modern-cpp-tutorial
//

#include <iostream>
#include <memory>

void foo(std::shared_ptr<int> i)
{
    (*i)++;
}

int main()
{
    // auto pointer = new int(10); // illegal, no direct assignment
    // std::shared_ptr construction
    auto pointer = std::make_shared<int>(10);
    auto pointer2 = pointer;    // reference count + 1
    auto pointer3 = pointer;    // reference count + 1
    
    
    foo(pointer);
    std::cout << *pointer << std::endl; // 11
    int *p = pointer.get();             // does not increase reference count
    
    std::cout << "pointer.use_count() = " << pointer.use_count() << std::endl;
    std::cout << "pointer2.use_count() = " << pointer2.use_count() << std::endl;
    std::cout << "pointer3.use_count() = " << pointer3.use_count() << std::endl;

    pointer2.reset();
    std::cout << "reset pointer2:" << std::endl;
    std::cout << "pointer.use_count() = " << pointer.use_count() << std::endl;
    std::cout << "pointer2.use_count() = " << pointer2.use_count() << std::endl;
    std::cout << "pointer3.use_count() = " << pointer3.use_count() << std::endl;
    
    pointer3.reset();
    std::cout << "reset pointer3:" << std::endl;
    std::cout << "pointer.use_count() = " << pointer.use_count() << std::endl;
    std::cout << "pointer2.use_count() = " << pointer2.use_count() << std::endl;
    std::cout << "pointer3.use_count() = " << pointer3.use_count() << std::endl;
    // std::cout << *pointer << std::endl; // reference count equals 0, illegal access


    // Before leaving the scope, the pointer is destructed and
    // the reference count is reduced to 0
    return 0;
}