That wouldn't compile.

To use the header I linked it should be `nonstd::observer_ptr<std::string> p(&strings[0]);`

You also need to dereference p to use the stream operator.

I'm disappointed you presented such a contrived example. You also deliberately avoid const-correctness. That's a little insidious. You need to const everything manually in C++, so as a good C++ programmer you should const everything as you write C++. Only carefully omit const when you need mutability.

We all know C++98 is dangerously unsafe. Let's write your example in C++11.

    #include <iostream>
    #include <string>
    #include <vector>
    #include <memory>
    #include <utility>
    #include "observer_ptr.h"

    // kill the noise
    using std::cout;
    using std::vector;
    using std::string;
    using nonstd::observer_ptr;

    int main() {
      vector<string const> const strings { "Hello" };
      observer_ptr<string const> const p(&strings[0]);
      strings.clear(); // not gonna happen
      cout << *p;
    }

    » clang++ -std=c++11 immutable.cpp
    immutable.cpp:11:5: error: member function 'clear' not viable: 'this' argument has type 'const std::vector<const std::string>' (aka 'const
          vector<const basic_string<char, char_traits<char>,     allocator<char> > >'), but function is not marked const
        strings.clear(); // not gonna happen
        ^~~~~~~
    /usr/local/Cellar/llvm/HEAD/bin/../include/c++/v1/vector:735:    10: note: 'clear' declared here
        void clear() _NOEXCEPT
             ^
    1 error generated.

EDIT: Down voted for legitimate rebuttal. Nice.