std::basic_ostream::~basic_ostream

From cppreference.com
virtual ~basic_ostream();

Destroys the basic_ostream object. This destructor does not perform any operation on the underlying streambuffer (rdbuf()): the destructors of the derived output streams such as std::basic_ofstream and std::basic_ostringstream are responsible for calling the destructors of the streambuffers.

[edit] Example

#include <sstream>
#include <iostream>
void add_words(std::streambuf* p)
{
    std::ostream buf(p); // buf shares the buffer with s
    buf << " is the answer";
} // calls the destructor of buf. p remains unaffected
int main()
{
    std::ostringstream s;
    s << 42;
    add_words(s.rdbuf());
    s << ".";
    std::cout << s.str() << '\n';
}

Output:

42 is the answer.