Re: [Boost-users] Segmentation fault when throwing exception?

Subject: Re: [Boost-users] Segmentation fault when throwing exception?
From: Emil Dotchevski (emildotchevski_at_[hidden])
Date: 2011-05-17 14:48:38

On Tue, May 17, 2011 at 6:11 AM, Germán Diago <germandiago_at_[hidden]> wrote:
> 2011/5/17 Germán Diago <germandiago_at_[hidden]>:
>>> To see what BOOST_THROW_EXCEPTION does exactly, read the following:
>>> http://www.boost.org/doc/libs/1_46_1/libs/exception/doc/BOOST_THROW_EXCEPTION.html
>>> http://www.boost.org/doc/libs/1_46_1/libs/exception/doc/throw_exception.html
>>
>> I already read it. But I can't figure out why it segfaults at all. I
>> have no idea.
>>
>
> I found the error. It had nothing to do with the macro. But I don't
> know wether this is a bug or not in class shared_ptr:
>
>
> I have a shared_ptr<FILE> f(fopen(file_that_doesnt_exists, "rb"),
> &fclose); call.
>
> If fopen returns null I think that the custom deleter is still called
> even if the class was constructed with a null pointer.
> Maybe I should make sure myself that fopen doesn't return NULL,
> because, anyway when you construct a shared_ptr
> you are passing a valid resource and it is not checked.

Not a bug; a shared_ptr may hold ownership of an object even when
shared_ptr::get() returns 0.

You could use

boost::shared_ptr<FILE> my_fopen( char const * name, char const * mode )
{
  if( FILE * f = fopen(name,mode) )
    return boost::shared_ptr<FILE>(f,fclose);
  else
    BOOST_THROW_EXCEPTION(file_open_error()<<
      boost::errinfo_errno(errno) <<
      boost::errinfo_api_function("fopen") <<
      boost::errinfo_file_name(name) <<
      boost::errinfo_file_open_mode(mode));
}

Emil Dotchevski
Reverge Studios, Inc.
http://www.revergestudios.com/reblog/index.php?n=ReCode