Обсуждение: Re: :PgSQL: More Queestions
On Wednesday, November 20, 2002, at 06:53 AM, Tim Bunce wrote:
>> But if I change it (as I'm seriously considering, in light of
>> PostgreSQL 7.3's support for prepared statements), I'll probably do no
>> parsing for comments.
>
> I think that would be a bad move.
Yes, your last post makes very clear why. Thanks.
> If it's seen the start of a string ("..." or '...') then it just
> keeps copying the string till it finds the same type of quote
> character to mark the end of the string. The 'fiddly bit in the
> middle' is handling backslashes used to escape quote chars in the
> middle of the string: "...\"..." and "...\\" (odd vs even number).
Seems rather opaque. Maybe I'm just reflecting my C-newbieness, but why
wouldn't this work as well? Borrowing a bit from DBD::ODBC here (but
allowing for both kinds of escaping of the quote characters):
if (*src == '"' || *src == '\'') { if (!in_literal) { literal_ch = *src;
in_literal = 1; } else { if (*src == literal_ch && *(src-1) != '//' &&
*(src-1)!= literal_ch) { in_literal = 0; } } }
> ANSI standard doesn't use backslashes, it uses doubling: "...""..."
Yeah, as Rudy pointed out, however, PostgreSQL uses backslashes as well
as doubling.
> Take a look at dbd_preparse in DBD::Oracle.
Will do, when I'm more awake again and find the tuits...
> There's also a preparse() in DBI.xs which was destined to become a
> standard service offered to drivers - but isn't quite ready yet.
Hrm, yes, that could be quite handy, since dbd_preparse() seems to be
one of the more complex driver functions...
Regards,
David
--
David Wheeler AIM: dwTheory
david@wheeler.net ICQ: 15726394
http://david.wheeler.net/ Yahoo!: dew7e Jabber:
Theory@jabber.org
On Wed, Nov 20, 2002 at 10:30:00PM -0800, David Wheeler wrote:
> On Wednesday, November 20, 2002, at 06:53 AM, Tim Bunce wrote:
>
> >>But if I change it (as I'm seriously considering, in light of
> >>PostgreSQL 7.3's support for prepared statements), I'll probably do no
> >>parsing for comments.
> >
> >I think that would be a bad move.
>
> Yes, your last post makes very clear why. Thanks.
>
> >If it's seen the start of a string ("..." or '...') then it just
> >keeps copying the string till it finds the same type of quote
> >character to mark the end of the string. The 'fiddly bit in the
> >middle' is handling backslashes used to escape quote chars in the
> >middle of the string: "...\"..." and "...\\" (odd vs even number).
>
> Seems rather opaque. Maybe I'm just reflecting my C-newbieness, but why
> wouldn't this work as well? Borrowing a bit from DBD::ODBC here (but
> allowing for both kinds of escaping of the quote characters):
>
> if (*src == '"' || *src == '\'') {
> if (!in_literal) {
> literal_ch = *src;
> in_literal = 1;
No need for in_literal as literal_ch can serve as a flag as well.
> } else {
> if (*src == literal_ch && *(src-1) != '//'
> && *(src-1) != literal_ch) {
> in_literal = 0;
> }
> }
> }
Can't distinguish between"....\\\\" - final double quote ends the string"...\\\\\" - final double quote is
escapedand string continues...
If the original code isn't broken it doesn't need fixing, maybe
just commenting.
Tim.
>
> On Wed, Nov 20, 2002 at 10:30:00PM -0800, David Wheeler wrote:
> > On Wednesday, November 20, 2002, at 06:53 AM, Tim Bunce wrote:
> >
> > >>But if I change it (as I'm seriously considering, in light of
> > >>PostgreSQL 7.3's support for prepared statements), I'll probably do no
> > >>parsing for comments.
> > >
> > >I think that would be a bad move.
> >
> > Yes, your last post makes very clear why. Thanks.
> >
> > >If it's seen the start of a string ("..." or '...') then it just
> > >keeps copying the string till it finds the same type of quote
> > >character to mark the end of the string. The 'fiddly bit in the
> > >middle' is handling backslashes used to escape quote chars in the
> > >middle of the string: "...\"..." and "...\\" (odd vs even number).
> >
> > Seems rather opaque. Maybe I'm just reflecting my C-newbieness, but why
> > wouldn't this work as well? Borrowing a bit from DBD::ODBC here (but
> > allowing for both kinds of escaping of the quote characters):
> >
> > if (*src == '"' || *src == '\'') {
> > if (!in_literal) {
> > literal_ch = *src;
> > in_literal = 1;
>
> No need for in_literal as literal_ch can serve as a flag as well.
True...I was hacking that in and overlooked it.
>
> > } else {
> > if (*src == literal_ch && *(src-1) != '//'
> > && *(src-1) != literal_ch) {
> > in_literal = 0;
> > }
> > }
> > }
>
> Can't distinguish between
> "....\\\\" - final double quote ends the string
> "...\\\\\" - final double quote is escaped and string
> continues...
>
> If the original code isn't broken it doesn't need fixing, maybe
> just commenting.
I'm tempted to leave it, since nobody is complaining, at the moment...but
I'll put it on the list.
Jeff