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From: Christopher Kohlhoff (chris_at_[hidden])
Date: 2005-09-15 01:43:03

Hi Eric,

--- Eric Niebler <eric_at_[hidden]> wrote:
> What you are describing, at least in regex terms, is a partial match.
> Ordinarily, a regex match will give you a "yes" or a "no" answer.
> With a
> partial match, you can get a "maybe" if the input sequence is
> exhausted
> before the regex state machine has reached its final state.

I was aware of partial matches from perusing the documentation a while
back, and I'm not sure that it's exactly the same thing -- please
correct me if i'm wrong.

>From my reading of the documentation, if I get a partial match and I
want to continue to try for a full match I must buffer the entire data
from the beginning of the partial match. This means that in the
partial_regex_grep example it cannot find a substring match that is
greater then 4096 characters long, because that is all the data it will

Furthermore, each time I want to retest the input against the
expression it must process the whole input string again. This is not
ideal from an efficiency point of view, since I could potentially
receive input data one byte at a time.

What I want is a stateful regular expression-based decoder object
(since in theory it's just a state machine and can remember its current
state). I can feed it more input which will cause more state
transitions, and it will tell me when it reaches a terminal state. I
never have to buffer more input than the block just read because
earlier input will have been fully consumed by the decoder.

As I said, this is an area I am very interested in exploring further
when time permits (and not just in relation to regular expressions, but
also things like Boost.Serialization), but that definitely belongs in
its own thread.


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