How to build a string on the fly, using std::ostringstream?

Does the Standard Library support creating an std::string by means of
streaming, without having to declare a *named* ostringstream object?  I
tried
the following:

   #include <sstream>
   #include <string>
   int i = 42;

   std::string s = (std::ostringstream() << "i = " << i).str();

Of course it didn't compile, because a temporary (std::ostringstream())
cannot
be passed as non-const reference to a function (operator<<).  Okay, second
try, wrapping the ostringstream as follows:

  template <typename T> class Wrapper {
   T m_data;
  public:
   T & get() {
    return m_data;
   }
  };

  std::string s = (Wrapper<std::ostringstream>().get() << "i = " <<
i).str();

Unfortunately it still didn't compile, because operator<< returns an
std::basic_ostream, instead of an std::ostringstream, and therefore it
doesn't
have an str() member function.  Now I wonder, is it safe to cast the
stream,
returned by operator<< to an ostringstream reference?  As follows:

  std::string s =
static_cast<std::ostringstream&>(Wrapper<std::ostringstream>().get()
     << "i = " << i).str();

At least, it *seems* to work...   But is it the proper way to do it?


Kind regards,
-- 
Niels Dekker
http://www.xs4all.nl/~nd/dekkerware
Scientific programmer at LKEB, Leiden University Medical Center

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