Re:bool

Re:bool

[Andrew Borthwick]

Per Bothner:
> sizeof(bool) must be one.
> Any other choice will be "unexpected" by reasonable progragrammers.

   I totally agree.  This behavior was certainly unexpected by me.

> Er - what has sizeof to do with how bits are packed?  Obviously, sizeof
> will only tell you the fixed (overhead) size.  If you look at
> bit_vector, you will find that it does use 1 bit per bool.

My apologies for a somewhat poor choice of words on the subject of vector<bool>
vs. bit_vector.

     I'm still not entirely clear.  Am I correct that bit_vector gives me
1 bit per bool but vector<bool> does not?  If this is so, couldn't vector be
easily specialized for vector<bool> to give this functionality in a more
standard fashion?

Thanks,
Andrew Borthwick

Re: bool

[Branko Cibej]

Andrew Borthwick wrote:

>     I'm still not entirely clear.  Am I correct that bit_vector gives me
> 1 bit per bool but vector<bool> does not?  If this is so, couldn't vector be
> easily specialized for vector<bool> to give this functionality in a more
> standard fashion?

    There was a long and heated debate about that some time ago in comp.std.c++. I
don't know what the status is now, but at that time the draft standard required
vector<bool> to be specialised so that it used one bit per bool, like bit_vector
does. The central problem was the very same space-vs.-time trade-off we have here.

Personally I think that having two different containers is the correct solution:
vector<bool> for fast access and bit_vector for compact storage -- and you can
always compromise with a vector<unsigned char>.

--
Branko Cibej   <branko.cibej@hermes.si>
HERMES SoftLab, Litijska 51, 1000 Ljubljana, Slovenia
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