I was testing how C++ manages memory and their allocation. I’ve stumbled on something I can’t seem to figure out. I’m sure it has a simple explaination, but the rabbithole on memory in general got to me. So I ask your help.

I know that if you have the following code, that the address of property A in B is unvalid because the stack will delete ‘a’ when it leaves the getvar() function.

#include <iostream>

class A{
public:
    int prop =  2;
};

class B{
public:
    A* prop;
};

void getvar(B&);

int val;

int main()
{
    B b;
    std::cout << &b <<"n";
    getvar(b);
    
    std::cout << b.prop <<"n";
    std::cout << &((*b.prop).prop);
}


void getvar(B& b){
    A a;
    b.prop = &a;
    std::cout << &a << "n";
    std::cout << &((*b.prop).prop);
}
    

However, following this logic I tested this code:

#include <iostream>

class Cap{
public:
    int param;
};

class Form{
public:
    Form() {
        Cap cap;
        cap.param = 4;
    }
    void func(){
        std::cout << &cap << "n";
    }
    int s = 5;
    Cap cap;
};

int main()
{
    Form form;
    std::cout << &form << "n";
    std::cout << &form.cap << "n";
    std::cout << &form.cap.param << "n";
    form.func();
    std::cout << form.cap.param << "n";

}

I assumed that, when the constructor of form is called, a new instance of cap is created. However, as soon as the program leaves the constructor, following the previous logic, I assumed the cap variable would be addressing released stack memory, and thus be invalid.

Now, the tests I made showed me that the cap property is alive and kicking but why?
And what if the cap property was a pointer (e.g. Cap* cap;) would it cause problems?
Thanks in advance!