Inline ostringstream macro reloaded

Referring to http://stackoverflow.com/questions/303562/c-format-macro-inline-ostringstream

The question there was for a macro that allows inline concatenation of objects to create a string, iostream-style.

The answer was:

#define SSTR( x ) dynamic_cast< std::ostringstream & >( \
        ( std::ostringstream().seekp( 0, std::ios_base::cur ) << x ) \
    ).str()

Usage (for example):

throw std::runtime_error(
        SSTR( "FooBar error: Value " << x << " exceeds " << y )
);

That works beautifully - with GCC. It compiles and runs under Visual C++ 2005, too. But with the latter, all uses of the macro result in empty strings, and I am quite dumbfounded as to why, and how to fix it...?

From stackoverflow

• Unfortunately I don't have access to a MSVC compiler to test against.

  In my past experiences with microsoft's tools, it seems like microsoft treats language definitions and standards as little more than a rough guide. (I've lost lots of time on projects only to discover microsoft broke tradition with something as basic as C99.)

  Given this regrettably situation, I suggest you experiment with a series of trivial programs. Things like:

  std::ostringstream() o;
  o.seekp( 0, std::ios_base::cur ) << "foo";
  cout << "Test1:  " << o << endl;
  

  Or perhaps:

  std::ostringstream() o;
  cout << "Test2:  " << typeid(o).name() << endl;
  cout << "Test3:  " << typeid(o.seekp( 0, std::ios_base::cur )).name() << endl;
  

  Try to see at what point things stop working. Then work around the problem from there.

  DevSolar : seekp() was the culprit. Not sure what MSVC++ does differently with that, but replacing ostringstream().seekp( 0, ios_base::cur ) with ostringstream() << std::dec (as cadabra suggested) works for MSVC++. I left a note on the original question so others don't get caught by it.