Use shared_ptr among member functions as private variable C++

Question

I would like to reuse the shared_ptr among a few member functions in a class.

#include <iostream>
#include <memory>

class TestClass
{
    private:
        std::shared_ptr<int> int_shared_ptr;

    public:
        TestClass()
        {
            std::cout << "I will create a shared ptr object here.";
            std::shared_ptr<int> int_ptr (new int(10));
            std::shared_ptr<int> int_shared_ptr(int_ptr);
            std::cout << "The created shared ptr has value of " << *int_shared_ptr << "\n";

        }

        void check_if_shared()
        {
            std::cout << "The created shared ptr has value of " <<  int_shared_ptr << "\n";
        }

};


int main(){

    auto tc = TestClass();
    tc.check_if_shared();


}

Output

I will create a shared ptr object here.The created shared ptr has value of 10
The created shared ptr has value of 0

The int_shared_ptr seems destroyed once it leaves the constructor. Can anyone suggest a way to keep the shared pointer after leaving the constructor?

Answer 1

The line

std::shared_ptr<int> int_shared_ptr(int_ptr);

creates a function local variable of the same name as the member variable. The member variable is left default-initialized. Use:

TestClass() : int_shared_ptr(new int(10))
{
    std::cout << "The created shared ptr has value of " << *int_shared_ptr << "\n";
}

It is more idiomatic to use std::make_shared:

TestClass() : int_shared_ptr(std::make_shared<int>(10))
{
    std::cout << "The created shared ptr has value of " << *int_shared_ptr << "\n";
}