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From: "f.heckenbach@fh-soft.de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/88508] std::bad_cast in
 std::basic_ostringstream<char16_t>.oss.fill()
Date: Wed, 05 Apr 2023 18:35:44 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D88508

Frank Heckenbach <f.heckenbach@fh-soft.de> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |f.heckenbach@fh-soft.de

--- Comment #2 from Frank Heckenbach <f.heckenbach@fh-soft.de> ---
According to
https://stackoverflow.com/questions/57406448/canot-read-char8-t-from-basic-=
stringstreamchar8-t
this seems to be the same issue, so I'm not filing a new bug, just adding a
comment.

Apparently this is no GCC bug, but according to the standard. IMHO this sho=
ws
how ridiculous the current UTF-8 support is. A common I/O manipulator (setw)
fails with an inscrutable error (bad cast, what cast?) which is even suppre=
ssed
by default, unless enabled with o.exceptions, so by the default the stream =
just
mysteriously stops working. And all that because the library doesn't know w=
hat
the space character is in UTF-8. Just ranting, I know, but it's silly.

% cat test.cpp
#include <sstream>
#include <fstream>
#include <iomanip>

int main ()
{
  std::basic_ostringstream <char8_t> o;
  o.exceptions (std::ifstream::badbit);
  o << std::setw (1) << u8"";
}
% g++ -std=3Dc++20 -Wall -Wextra -o test test.cpp=20=20
% ./test
terminate called after throwing an instance of 'std::bad_cast'
  what():  std::bad_cast
Aborted=