Does String objects in C++ have null character?

We all know that strings have a null character in the end. The normal declaration is:

char message[];

I am not talking about this. I am talking about string object in C++ which is defined as:

string message;

Now I read in a book today by Jones and Bartlett publishers, and they said,

Object of class strings do not necessarily contain the string terminating character '\0' as in the case with C strings.

I searched it on net (obviously..😛) and couldnt find any convincing answer. Anyone care to throw some light?