modern-cpp-tutorial/code/5/5.2.unique.ptr.cpp

//
// 5.2.unique.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>

struct Foo {
    Foo()      { std::cout << "Foo::Foo" << std::endl;  }
    ~Foo()     { std::cout << "Foo::~Foo" << std::endl; }
    void foo() { std::cout << "Foo::foo" << std::endl;  }
};

void f(const Foo &) {
    std::cout << "f(const Foo&)" << std::endl;
}

int main() {
    std::unique_ptr<Foo> p1(std::make_unique<Foo>());
    
    // p1 is not empty, prints
    if (p1) p1->foo();
    {
        std::unique_ptr<Foo> p2(std::move(p1));
        
        // p2 is not empty, prints
        f(*p2);
        
        // p2 is not empty, prints
        if(p2) p2->foo();
        
        // p1 is empty, no prints
        if(p1) p1->foo();
        
        p1 = std::move(p2);
        
        // p2 is empty, no prints
        if(p2) p2->foo();
        std::cout << "p2 was destroyed" << std::endl;
    }
    // p1 is not empty, prints
    if (p1) p1->foo();
    
    // Foo instance will be destroyed when leaving the scope
}