https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123100
--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to M Welinder from comment #0)
> std::ostringstream os;
>
> char buf[100] = {};
> os.rdbuf()->pubsetbuf(buf, sizeof buf);
What do you expect this to do?
"Effects: implementation-defined, except that setbuf(0, 0) has no effect."
