vector related memory allocation question

c++, stdvector

Solution

You need to implement a copy constructor and an assignment operator for Foo. Whenever you find you need a destructor, you alnmost certainly need these two as well. They are used in many places, specifically for putting objects into Standard Library containers.

The copy constructor should look like this:

Foo :: Foo( const Foo & f ) : my_a( new A( * f.my_a ) ) {
}

and the assignment operator:

Foo & Foo :: operator=( const Foo & f ) {
    delete my_a;
    my_a = new A( * f.my_a );
    return * this;
}

Or better still, don't create the A instance in the Foo class dynamically:

class Foo {      
      public:
             Foo();
             ~Foo();
             void createA();
             A my_a;
};

Foo::Foo() : my_a( 20 ) {
};

Problem

I am encountering the following bug. - I have a class `Foo` . Instances of this class are stored in a std::vector `vec` of `class B`. - in class Foo, I am creating an instance of class A by allocating memory using `new` and deleting that object in `~Foo()`. the code compiles, but I get a crash at the runtime. If I disable `delete my_a` from desstructor of class `Foo`. The code runs fine (but there is going to be a memory leak). Could someone please explain what is going wrong here and suggest a fix? thank you! ``` class A{ public: A(int val); ~A(){}; int val_a; }; A::A(int val){ val_a = val; }; class Foo { public: Foo(); ~Foo(); void createA(); A* my_a; }; Foo::Foo(){ createA(); }; void Foo::createA(){ my_a = new A(20); }; Foo::~Foo(){ delete my_a; }; class B { public: vector<Foo> vec; void createFoo(); B(){}; ~B(){}; }; void B::createFoo(){ vec.push_back(Foo()); }; int main(){ B b; int i =0; for (i = 0; i < 5; i ++){ std::cout<<"\n creating Foo"; b.createFoo(); std::cout<<"\n Foo created"; } std::cout<<"\nDone with Foo creation"; std::cout << "\nPress RETURN to continue..."; std::cin.get(); return 0; } ```

Original source