Boost logo

Boost :

From: Edward Diener (eddielee_at_[hidden])
Date: 2003-08-07 21:10:55

Edward Diener wrote:
> Ross Smith wrote:
>> George A. Heintzelman wrote:
>>>> Given that I have a string 's' from somewhere, I'd like to create a
>>>> regular expression where some part must match that string. The
>>>> problem is, the 's' could contain characters that have a special
>>>> meaning in regular expressions. Is there some support function that
>>>> can provide an escaped version of 's'? Something that transforms
>>>> "my.*string" into "my\.\*string"? If there isn't, would it be
>>>> possible/easy to provide one?
>>> Second that request. I just had a need for this, though I wound up
>>> ignoring the problem rather than fixing it...
>> There must be something in the air; I just had a need for this too.
>> My quick-and-dirty solution was to simply replace every
>> non-alphanumeric character with a hex escape sequence (\xNN).
>> Having it just add escapes to a list of special characters wouldn't
>> work as a general solution, because the list of characters depends on
>> the
>> flags passed to the regex functions.
> That is a good point. However you always know what flags are passed
> to the regex function since they are available. That's not arguing
> against such a function as being part of the library itself but it is
> still doable by you. Furthermore you can set the flag mode you like
> to simplify your escaping,
> but of course this is not a general solution as the rest of the
> regular expression may require particular flags set.
>> Of course there are settings
>> where
>> my hex-escape solution won't work either. I don't think a general
>> solution is possible without making it part of the library; it needs
>> access to the innards of the regex objects in order to know the exact
>> syntax they recognise.
> That is not true. One just needs to read and understand the
> documentation on the particular flags and what they mean. There are
> no "secret innards" which retain information about escaping
> characters which you can't find for yourself by testing the flags.

Let me add to my remark by saying that it is true that you can change the
characters of a regular expression using localization with a dll or message
catalog, but again you know what changes have been made and should be able
to escape the appropriate characters.

Boost list run by bdawes at, gregod at, cpdaniel at, john at