Re: Modification of trailing null character in std::basic_string

According to N3376 - 21.4.5/2

     reference operator[](size_type pos);

     Returns: *(begin() + pos) if pos< size(). Otherwise, returns a
     reference to an object of type charT with value charT(), where
     modifying the object leads to undefined behavior.

If my understanding of this rule is correct, we can't safely assign
zero value to the trailing null character in a string object, even
if the string is non-empty:

1)
     std::string s;
     char&c = s[0]; // well-defined
     assert(c == '\0'); // succeeds
     c = '\0'; // undefined
2)
     std::string s = "text";
     char&c = s[s.size()]; // well-defined
     assert(c == '\0'); // succeeds
     c = '\0'; // undefined

and the following implementation of get_window_text_w is not
well-defined:

     #include<string>
     #include<windows.h>

     std::wstring get_window_text_w(HWND hwnd)
     {
         std::wstring result;
         result.resize(GetWindowTextLengthW(hwnd));
         GetWindowTextW(hwnd,&result[0], result.size() + 1);
         return result;
     }

(here GetWindowTextW assigns zero value to the trailing null
character), so we need to use extra character for such C API calls:

     std::wstring get_window_text_w(HWND hwnd)
     {
         std::wstring result;
         result.resize(GetWindowTextLengthW(hwnd) + 1);
         GetWindowTextW(hwnd,&result[0], result.size());
         result.pop_back();
         return result;
     }

Did I miss something?