deriving from vectors

[tspga]

i want to derive a class named population which is derived from vectors of solution and solution class is derived from vectors of int. that means that population is collection of solutions and is created with vector by deriving it from template based vectors<solution>. my question is that im bit confused in this hierarchy and not getting idea of constructors and destructors and calling mechanism of methods. i do have concepts of inhertince and constructors in inheritence but confused in this perspective.

[laserlight]

It sounds like what you should do is to define a solution class that has a vector of int as a member variable, then define a population class that has a vector of solution objects as a member variable.

[nuzzle]

You shouldn't derive from STL containers such as vector. They lack virtual destructors which opens up for memory leaks and undefined behaviours.

Instead base your design on classes you define yourself and use STL containers for implementation purposes only.

[thefollower]

You shouldn't derive from STL containers such as vector. They lack virtual destructors which opens up for memory leaks and undefined behaviours.

Could that be followed by an example please ?

I can't imagine how a coder freed the allocated objects used in the derived class has no influence over their base objects' remains.

[laserlight]

Could that be followed by an example please ?

Attempting to delete a derived class object through a pointer to its base class results in undefined behaviour if the base class destructor is not virtual. Since it is undefined behaviour, an example does not guarantee that you'll see any specific results.

I can't imagine how a coder freed the allocated objects used in the derived class has no influence over their base objects' remains.

Suppose the derived class destructor frees some memory. Now, you use delete on a pointer to the base class that points to this derived class object. We could speculate that perhaps only the base class destructor is called; after all, it is non-virtual. If this happens, then the memory that should have been freed will not be freed.

[nuzzle]

Could that be followed by an example please ?

It's stated in the C++ standard (5.3.5 delete, paragraph 3):

"... if the static type of the object to be deleted is different from its dynamic type, the static type shall be a base class of the dynamic type of the object to be deleted and the static type shall have a virtual destructor or the behavior is undefined..."

This means that if you do,

class A {};
class B : public A {};
//
A* x = new B;
delete x;

you have undefined behaviour because A lacks a virtual destructor.

And since vector doesn't have a virtual destructor you get undefined behaviour if you use it in place of A.

Note that C++ is significantly different from more OO specialized languages such as Java. C++ doesn't have a common "mother" base class like Java has. It's substantially more important in C++ to make sure a class is designed to act base class before one uses it as such.

So don't use STL containers polymorphically. Use them as implementation detail only.

[tspga]

i have seen some sample code like class CVector : public std::vector<T> on same lines if we write class solution: public vector <int> now my next question is whether vector<int> is member variable here or some class ? because it looks like it should be member variable but if so then y it is written in class like manner of inheritence?

[laserlight]

i have seen some sample code like class CVector : public std::vector<T> on same lines if we write class solution: public vector <int> now my next question is whether vector<int> is member variable here or some class ? because it looks like it should be member variable but if so then y it is written in class like manner of inheritence?

It would be a class, not a member variable; you would be looking at a case of public inheritance from std::vector<int>.

[tspga]

so u suggests it being as member variable? but i want to do it in the way i described means like class solution: public vector<int> whats the difference i mean do not tell that ur one is called composition and mine is inheritence i want to ask how to initialize them in my case that is inheritence

[laserlight]

so u suggests it being as member variable?

Yes.

but i want to do it in the way i described means like class solution: public vector<int> whats the difference

Why do you want to use public inheritance here? nuzzle and I already explained to you why not in posts #3, #5 and #6.

[tspga]

regards...