Re: [Boost-users] [Iostreams] How to check whether file has been opened?

Subject: Re: [Boost-users] [Iostreams] How to check whether file has been opened?
From: Daniel Eiband (eiband_at_[hidden])
Date: 2010-03-31 11:15:49

> The original maintainer is no longer active. Daniel James has started to
> process patches. So the fastest way to remove that problem is adding a
> patch to your ticket.

Hi,

I am quite new to the Iostreams library and just started to implement my 
first devices. I am willing to deliver a patch, but this is not a 
trivial problem. I looked into the documentation and the users guide 
tells the following about exception policies:

http://www.boost.org/doc/libs/1_42_0/libs/iostreams/doc/index.html

- "These member functions throw exceptions to report errors": So the 
best a file device can do when opening fails is throwing a failure 
exception. This is currently not the case (e.g. basic_file ignores the 
return value of the filebuf::open() call).

- "With streams, therefore, the user has a choice whether to enable 
exceptions": This is currently not the case for 
boost::iostreams::stream. Exceptions of devices (which is the 
recommended/only way of reproting errors in devices) are passed to the 
user code ignoring exception masks. Furthermore, the failbit is not set 
when an operation like open fails (also see bug 
https://svn.boost.org/trac/boost/ticket/3935)

Two actions that pop up to my mind:

-> Considering the design choice in the above mentioned exception 
documentation, file devices must throw exceptions when open(), close(), 
... fails.

-> The ugly part: Ignore failbit/badbit/eofbit and exception mask or 
translate exceptions back to iostate for boost::iostreams::stream? This 
affects not only opening or closing the stream but also all other 
exceptions e.g. bad_seek() (failbit also not set in current implementation).

Should this discussion go to a different mailing list? Who is more 
experienced with iostreams?

Kind regards,

Daniel