<sstream> is used by dlib (dlib.net). I am using dlib in my project

I guess that means you'll need sstream ;-)

There's a reply on stackoverflow that indicates that the problem is that one of the standard perl headers defines "setbuf".
I find that the following compiles ok for me:

use strict;
use warnings;

use Inline CPP => <<'CPP';

#undef seekdir
#ifdef _WIN32
#undef setbuf
#endif
#include <sstream>

CPP

1;
[download]

So see how that works for you.

Cheers,
Rob