C++ Destructors with Vectors, Pointers,

Question

As far as I know, I should destroy in destructors everything I created with new and close opened filestreams and other streams. However, I have some doubts about other objects in C++:

• std::vector and std::strings: Are they destroyed automatically?

• If I have something like

  std::vector<myClass*>  

  of pointers to classes. What happens when the vector destructor is called?
  Would it call automatically the destructor of myClass? Or only the vector is destroyed but all the Objects it contains are still existant in the memory?

• What happens if I have a pointer to another class inside a class, say:

  class A {   ClassB* B; } 

  and Class A is destroyed at some point in the code. Will Class B be destroyed too or just the pointer and class B will be still existent somewhere in the memory?

Answer 1

std::vector and std::strings: Are they destroyed automatically?

Yes (assuming member variables are not pointers to std::vector and std::string).

If I have something like std::vector what happens when the vector destructor is called? Would it call automatically the destructor of myClass? Or only the vector is destroyed but all the Objects it contains are still existant in the memory?

If vector<MyClass> then all objects contained in the vector will be destroyed. If vector<MyClass*> then all objects must be explicitly deleted (assuming the class being destructed owns the objects in the vector). A third alternative is vector of smart pointers, like vector<shared_ptr<MyClass>>, in which case the elements of the vector do not need to be explictly deleted.

What happens if I have a pointer to another class inside a class

The B must be explicitly deleted. Again, a smart pointer could be used to handle the destruction of B.

Answer 2

You only need to worry about for the memory you have created dynamically (When you reserve memory with new.)

For example:

Class Myclass{    private:        char* ptr;    public:        ~Myclass() {delete[] ptr;}; }