https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59267
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |INVALID
Status|UNCONFIRMED |RESOLVED
--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to James from comment #0)
> Created attachment 31285 [details]
> A very simple C++ program and Makefile that compiles without warning, but
> also optimizes out some necessary code.
Nothing is optimized out, you are misinterpreting the behaviour.
After the 'is >> val' extraction the stream state has eofbit set, because you
read to the end of the stream.
That means the 'is << val' insertion fails, because is.good() is false. You
could have verified that quite easily:
is >> val;
is.str("");
if (is << val)
{
cout << "Read value " << val << ", number of characters: " <<
is.str().size() << ", input string " << s << ", resultant string: " << is.str()
<< endl;
}
else
cout << "Failed to write\n";
This prints "Failed to write" instead of "Read value ..."
So obviously is.str() returns an empty string, because you didn't insert
anything into the stream. You need to use is.clear() after reading up to EOF if
you want to insert into it again.
