What is the order of object destruction if we pass user defined object in stl container?

Question

For checking the order of destruction of user defined object in stl container, I have tested following code

class A
{
public: 

    static int i;
    const int j;
    A():j(++i)
    {
        cout<<"A::A() "<< j <<endl;
    }

    ~A()
    {
        cout<<"A::~A(): "<< j <<endl;
    }
    A(const A & obj):j(++i)
    {
        cout<<"copyconstro " << j <<endl;
    }
};

int A::i = 0;
int main()
{
    vector<A> obj;
    A ab; //1
    A ad;// 2
    A c;//3
    obj.push_back(ab); //4

    vector<A> obj2;
    obj2.push_back(c); //5
}

output:

A::A() 1
A::A() 2
A::A() 3
copyconstro 4
copyconstro 5
A::~A(): 5
A::~A(): 3
A::~A(): 2
A::~A(): 1
A::~A(): 4

I am little confused after looking at output.

Does ISO C++ standard mandate any sort of destruction order of objects inside STL containers?

score 2 · Answer 1 · answered Mar 27 '14 at 05:31

2

The order of destruction is the reverse order in which they are constructed. In your function, the order of destruction is:

obj2
c
ad
ab
obj

When obj2 gets destructed, it destructs 5.

When c gets destructed, it destructs 3.

When ad gets destructed, it destructs 2.

When ab gets destructed, it destructs 1.

When obj gets destructed, it destructs 4.

answered Mar 27 '14 at 05:31

R Sahu

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The question is about the order of object destruction inside STL containers, which is as TonyD pointed out [unspecified](http://stackoverflow.com/a/2083629/2507444). – Peter Clark Mar 27 '14 at 09:27

score 2 · Answer 2 · answered Mar 27 '14 at 05:33

Your code doesn't illustrate anything about "destruction order of objects inside STL containers" - each container only has one element. You're observing order of (creation and) destruction of function-local variables: notice destruction is the reverse of construction order, and specifically that construction of 4 happens when obj is defined, not when a copy of ab is push_back-ed into it, hence "4" being destroyed last.

Anyway, to actually answer your question - no - the Standard doesn't specify element destruction order.

What is the order of object destruction if we pass user defined object in stl container?

2 Answers2