c++ strings vs vector<char> vs dynamic arrays - c++

Question

I was trying to use char* pointers to refer to strings and vector<char> & dynamic arrays & I have a doubt with the following results :-
CODE 1:-
#include <iostream>
#include <string>
using namespace std;
int main()
{
cout<<"executing...\n";
string s="abcde";
char *c=&s[0];
cout<<c<<"\n";
s.~string();
cout<<c<<"\n";
cout<<"executed";
return 0;
}
The output of this code is :-
executing...
abcde
abcde
executed
CODE 2:-
#include <iostream>
#include <vector>
using namespace std;
int main()
{
cout<<"executing...\n";
vector<char> v {'a','b','c','d','e'};
char *p=&v[0];
cout<<p<<"\n";
v.~vector();
cout<<p<<"\n";
cout<<"executed";
return 0;
}
The output for this code is :-
executing...
abcde
executed
CODE 3 (with dynamic arrays):-
#include <iostream>
using namespace std;
int main()
{
cout<<"executing...\n";
char* c=new char[20] {'a','b','c','d','e'};
char *p=c;
cout<<p;
delete[] c;
cout<<"\n"<<p<<"\n";
cout<<"executed";
return 0;
}
The output for this code is similar to CODE 2:-
executing...
abcde
executed
I want to know why CODE 1 produces an output different from CODE 2 & CODE 3 ? What problem does string have that it behaves differently from vector<char> & dynamic arrays ?

Answer 1

All the snippets of code access data that has been deleted, which has no defined behavior. Therefore, any further assumption is meaningless and left to the single case. Whether you're accessing a vector, char*, string there's no difference: it's always the same violation.

Answer 2

Well I guess this example is good enough to show that your objects of string & vector are deleted twice hence leading to undefined behaviour :-
#include <iostream>
using namespace std;
class X
{
int x;
public:
X()
{
cout<<"constructing\n";
}
// other member functions...
~X()
{
cout<<"destroying\n";
}
};
int main()
{
X object;
object.~X();
return 0;
}
Output will be :-
constructing
destroying
destroying
When behaviour is undefined there is no use of thinking about "WHY SUCH AN OUTPUT", etc stuffs !! Even I had a doubt regarding the reference counting of C++ strings but as many people are saying strings are no longer reference counted so CODE 1 is also producing undefined behaviour. However I liked you experimenting with codes. It's necessary to learn a language properly. Keep it up !!!