Re: [Boost-users] [IOStreams] Is such a behaviour considered as bug

Subject: Re: [Boost-users] [IOStreams] Is such a behaviour considered as bug
From: Ovanes Markarian (om_boost_at_[hidden])
Date: 2011-08-17 18:22:21

Hello Daniel,

thanks for your answers. Please see my answers below.

On Fri, Aug 12, 2011 at 11:37 PM, Daniel James <dnljms_at_[hidden]> wrote:

> On 11 August 2011 14:22, Ovanes Markarian <om_boost_at_[hidden]> wrote:
> >
> > If the defined stream is only 2 bytes long why is 2 a valid stream
> position?
>
> There needs to be an offset for the end of the stream. I'm actually
> not sure if it should be -1 for larger values though.
>
To be honest, I do not understand what offset do you mean here. Why does
array_device needs an offset for the end of stream and stringstream does
not? I looked up the behavior in the standard (for stringstream, since I
assume array_device should behave similar in regards of positioning and
memory related nature of stringstream) and there is clearly written that
seeking to an invalid pos will cause tellg to return -1. I would propose to
change the array_device to be more consistent with stringstream in these
regards.
In Standard C++ IOStreams and Locales by A. Langer & K. Kreft is also stated
for basic_istream<char_type, traits_type>& seekg(...) on p.489:
"Repositions this to the location designated by pos, by calling
this->rdbuf()->pubseekpos(off) [or] (off,dir). !!! Failures are indicated by
the state of *this.!!! [...]"
And now the tellg counterpart:
"If this->fail()==true, returns pos_type(-1), othewise [...]"
In case of stringstream seekg immediately fails if seeking the stream to an
invalid pos, without any offsets. I find the behavior of array_device
somehow unnatural, especially for the case where I would like to mimic other
std streams for easier testing.

> > Why is eof always false? Do you think this behavior is buggy?
>
> IIRC in streams eof is only set when you try to read past the end of the
> file.
>
Yes, you are right. I double checked this in the Standard. As the my upper
answer points out, the stream should be in the failed state.

Many thanks for your time,
Ovanes