Order of constructor call in STL - c++

Question

I recently read simple STL sources,Here is the code:
#include <iostream>
#include <cstddef>
using namespace std;
class alloc
{
};
template <typename T, typename Alloc = alloc, size_t Bufsiz = 0>
class deque
{
public:
deque() { cout << "deque()" << endl; }
};
template <typename T, typename Sequence = deque<T> >
class stack
{
public:
stack() { cout << "stack()" << endl; }
private:
Sequence c;
};
int main()
{
stack<int> x;
return 0;
}
The output:
deque()
stack()
When i created a stack object,it should have called stack constructor first.But the fact is not.
Why the compiler calls deque constructor first?

Answer 1

Before you enter the body of a constructor, base class constructors are called, then all non-static member variables are default initialized in the order of declaration, unless they appear in a member initialization list. In your code Sequence c is initialized first and then the body of Stack::Stack() is executed.
This program illustrates the order of construction - destruction.
#include <iostream>
#include <string>
using namespace std;
struct Base_1
{
Base_1()
{
cout << "Base_1\n";
}
~Base_1()
{
cout << "~Base_1\n";
}
};
struct Base_2
{
Base_2()
{
cout << "Base_2\n";
}
~Base_2()
{
cout << "~Base_2\n";
}
};
struct Member_1
{
Member_1()
{
cout << "Member_1\n";
}
~Member_1()
{
cout << "~Member_1\n";
}
};
struct Member_2
{
Member_2()
{
cout << "Member_2\n";
}
~Member_2()
{
cout << "~Member_2\n";
}
};
struct Member_non_default
{
Member_non_default( string s )
{
cout << "Member non default\n";
}
~Member_non_default()
{
cout << "~Member non default\n";
}
};
struct Static_member
{
Static_member()
{
cout << "Static member\n";
}
~Static_member()
{
cout << "~Static member\n";
}
};
struct Derived: Base_1, Base_2
{
Member_1 m1;
Member_non_default m;
Member_2 m2;
static Static_member sm;
Derived():
m { "Member non default\n" }
{
cout << "Derived\n";
}
~Derived()
{
cout << "~Derived\n";
}
};
Static_member Derived::sm;
int main()
{
Derived d;
}
Output
Static member
Base_1
Base_2
Member_1
Member non default
Member_2
Derived
~Derived
~Member_2
~Member non default
~Member_1
~Base_2
~Base_1
~Static member