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List: cfe-dev
Subject: Re: [cfe-dev] libc++ and std::bad_exception
From: Howard Hinnant <hhinnant () apple ! com>
Date: 2011-07-30 23:39:11
Message-ID: 6460BD73-2553-4F5E-BC6C-AC619038C835 () apple ! com
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On Jul 30, 2011, at 5:53 PM, Seth Cantrell wrote:
> I've observed some unexpected behavior with libc++ and exception specifications. \
> libc++ seems to be calling std::terminate() even in a situation where it should \
> not.
> I have a program with a function 'foo' that lists std::bad_exception in its \
> exception specification, and a custom unexpected hander is registered which \
> rethrows an exception. When 'foo' is called it throws a type not listed and so my \
> custom unexpected handler is called. However, if I'm using libc++ then after my \
> handler is called std::terminate() is called.
> My understanding is that these circumstances should lead to std::bad_exception \
> being thrown and exception handling continuing normally instead of std::terminate() \
> being called.
Your understanding is correct.
>
> Here's the program I'm using:
>
> > #include <iostream>
> > #include <exception>
> >
> > void custom_unexpected() {
> > std::cerr << "custom unexpected handler called\n";
> > throw;
> > }
> >
> > void foo()
> > throw(std::bad_exception)
> > {
> > throw 10;
> > }
> >
> > int main (void) {
> > std::set_unexpected(custom_unexpected);
> >
> > try {
> > foo();
> > } catch (std::exception &e) {
> > std::cerr << "caught std::exception: " << e.what() << "\n";
> > }
> > }
> >
>
>
> Two commands I use to build this program were:
>
> > /usr/local/bin/clang++ -std=c++0x -U__STRICT_ANSI__ -Wall -Werror noexcept.cpp
>
> and
>
> > /usr/local/bin/clang++ -std=c++0x -stdlib=libc++ -U__STRICT_ANSI__ -Wall -Werror \
> > noexcept.cpp
>
> With the first build command the output of the resulting program is:
>
> > custom unexpected handler called
> > caught std::exception: std::bad_exception
>
> The program resulting from the second command (which uses libc++) outputs:
>
> > custom unexpected handler called
> > terminate called throwing an exceptionAbort trap: 6
>
>
> The result is also independent of whether I use -std=c++0x or not.
>
>
> version info:
>
> clang version 3.0 (http://llvm.org/git/clang.git \
> 1e5b6f60e2e09addd2f2e915c87d8bd74d40c369)
> Target: x86_64-apple-darwin11.0.0
> Thread model: posix
>
> and I believe the version of libc++ I'm using is the built in one with Mac OS X \
> Lion 10.7 (11A511)
Please file a bug report (http://llvm.org/bugs/) against libc++abi.
Because dynamic exception specifications have been deprecated, I do not know how much \
priority this bug will get. But it is an open source project. So if people are \
excited about getting this right, it will happen.
>
> I'd like to test it out with the latest version of libc++ as well, just to be sure \
> this isn't already fixed. Is there a recommended way to build and use libc++ \
> without replacing the system's version?
To build, I like to cd into lib and type ./buildit. You'll first want to: export \
TRIPLE=-apple_.
To run, create an environment variable with: export DYLD_LIBRARY_PATH="where ever you \
put the dylib". Mac OS will look there before it goes to the system places to load \
the library. And I believe a -I to your test headers (on the command line) will take \
precedence over the system headers as well.
Howard
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