[C++] smart pointer

smart pointer automatically managing memory a pointer  . if out of scope range, It deleted.

There are three types pointer in std namespace.

- unique_ptr

- shared_ptr

- weak_ptr

First unique_ptr code.

#include <iostream>
#include <memory>
int main(){
    // unique ptr
    std::unique_ptr<char> ch = std::make_unique<char>('c');
    auto a = std::make_unique<int>(1);

    std::cout << "ch: " << *ch << std::endl;
    std::cout << "a: " << *a << std::endl;
    decltype(a) ptr = a;        // compile error 
    std::cout << "a: " << *a << std::endl;
    return 0;
}
 

error message    

Second shared_ptr  continue code

#include <iostream>
#include <memory>
 
 
int main(){
    // unique ptr
    std::unique_ptr<char> ch = std::make_unique<char>('c');
    auto a = std::make_unique<int>(1);
    std::cout << "ch: " << *ch << std::endl;
    std::cout << "a: " << *a << std::endl;
 
    /*
    decltype(a) ptr = a;        // compile error 
    std::cout << "a: " << *a << std::endl;
    */
 
    std::shared_ptr<int> num = std::make_shared<int>(1);
    std::cout << "num: " << *num << std::endl;
    std::cout << "num reference count : " << num.use_count() << std::endl;
    std::shared_ptr<int> nptr = num;
    std::cout << "nptr: " << *nptr<< std::endl;
    std::cout << "num reference count : " << num.use_count() << std::endl;
    std::cout << "nptr reference count : " << nptr.use_count() << std::endl;
 
 
    {
        std::shared_ptr<int> nptr2 = num;
        std::cout << "scope in" << std::endl << std::endl;;
        std::cout << "nptr2: " << *nptr2 << std::endl;
        std::cout << "num reference count : " << num.use_count() << std::endl;
        std::cout << "nptr reference count : " << nptr.use_count() << std::endl;
        std::cout << "nptr2 reference count : " << nptr2.use_count() << std::endl;
    }
 
    // reference count down. automatically deleted.
    std::cout << "scope out" << std::endl << std::endl;;
    std::cout << "num reference count : " << num.use_count() << std::endl;
    std::cout << "nptr reference count : " << nptr.use_count() << std::endl;
    return 0;
}
 

Result

I'll be update more