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: Roland Bock (rbock_at_[hidden])
Date: 2010-04-01 05:25:10

Daniel Eiband wrote:
>> The original maintainer is no longer active.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

Hi,

when it comes to the iostream internals, I am quite new to the library 
myself. I am mostly using it for memory mapped files and 
compression/decompression. The latter has some bugs, too, for which I 
hope to find the time to send patches eventually...

I guess you should take the discussion to the boost developers list.

Regards,

Roland