Re: How to build a string on the fly, using std::ostringstream? [Reposting]

On Apr 27, 2:29 pm, Brendan Miller <catph...@[EMAIL PROTECTED]
> wrote:
> >>       using ::operator <<; // Note: Ugly disambiguation.
> Is this using statement really necessary? What ambiguity exists?

See my reply to Niels. I was unclear on the reason for the using
statement. As you point out its only use is for disambiguation. The
global namespace is of course always searched, but with the using
declaration any matching global operator becomes the preferred.

I have since removed the using statement because I found better
solutions in the client code were lookup problems occurred.

> >> Usage:
> >>   string s = S () << "i = " << i;
>
> > Cool!!!  It looks much better than my approach!
>
> Yes and much better than mine, which I was proud of up until now. This
> strikes me as the One True Way of inline stringbuilding.

In the search for the ultimate terseness:

   const struct StringBuilderFactory
   {
     struct StringBuilder
     {
       std::auto_ptr <std::ostringstream> s;

       StringBuilder ()
         : s (new std::ostringstream ())
       {}

       template <typename T>
       inline StringBuilder& operator << (const T& v)
       {
         *s << v;
         return *this;
       }

       inline operator std::string () const
       {return s->str ();}
     };

     template <typename T>
     StringBuilder operator << (const T& obj) const
     {return StringBuilder () << obj;}
   }
   S;

Usage:

   string s = S << "i = " << i;

Here S is a global instance of StringBuilderFactory. But it has no
state of its own so that's OK. The major drawback with this solution
is that it is slower due to the dynamic allocation of the stream.
Unfortunately dynamic allocation is required here because streams
cannot be copied and hence not returned from StringBuilderFactory. The
next C++ standard, C++0x, will fix this with move constructors for
streams.

If anyone has a C++03 solution to this problem, it would be nice to
see.

Regards,
Vidar Hasfjord

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