Pattern matching programming

Pattern matching programming

[fabio]

Hello,

I am trying to code a small C program that basically takes a long text
file with data that comes from a mysql server.

But I realize It is better to use regular expression. This is an examples
of the text:

=1 <p> blah </p> <div foo>{$foobar}</div>blah.... <p>linux rulez</p>
misc characters.... =2 blah blah <p> linux rulez again</p>.... <p>foo</p?blah


And so on.

The patterns are:

The record is represented by an equal. Ej, record 1 is "=1", record 2 is
"=2" and so on.

The desired text is where "linux rulez" is inside, it is the FIRST <p>
</p> AFTER a record.

So, I see that program this makes no sense because it is better to use sed
and awk.

The result I want to have is something like:

1 linux rulez
2 linux rulez again
3 linux rulez so far
...etc

The idea is elimate all <div>'s tags, then get the numbers (maybe with awk
-F"="), and then get the next <p> taq, remove the tags themself and
numbers and then the text and do the same procedure for all the 65230
records.

Thanks alot for any comment, sorry for the 'offtopic'

Kind regards,

fabio

Re: Pattern matching programming

[Fabrizio Sestito]

On Wednesday 18 May 2005 17:36, fabio@crearium.com wrote:
> Hello,
>
> I am trying to code a small C program that basically takes a long text
> file with data that comes from a mysql server.
>
> But I realize It is better to use regular expression. This is an examples
> of the text:
>
> =1 <p> blah </p> <div foo>{$foobar}</div>blah.... <p>linux rulez</p>
> misc characters.... =2 blah blah <p> linux rulez again</p>....
> <p>foo</p?blah
>
>
> And so on.
>
> The patterns are:
>
> The record is represented by an equal. Ej, record 1 is "=1", record 2 is
> "=2" and so on.
>
> The desired text is where "linux rulez" is inside, it is the FIRST <p>
> </p> AFTER a record.
>
> So, I see that program this makes no sense because it is better to use sed
> and awk.
>
> The result I want to have is something like:
>
> 1 linux rulez
> 2 linux rulez again
> 3 linux rulez so far
> ...etc
>
> The idea is elimate all <div>'s tags, then get the numbers (maybe with awk
> -F"="), and then get the next <p> taq, remove the tags themself and
> numbers and then the text and do the same procedure for all the 65230
> records.
>
> Thanks alot for any comment, sorry for the 'offtopic'
>
> Kind regards,
>
> fabio
>
Why don't you use an XML parser library?

Fabrizio

Re: Pattern matching programming

[Hareesh Nagarajan]

On 5/18/05, Fabrizio Sestito <lain@neotes.org> wrote:
> On Wednesday 18 May 2005 17:36, fabio@crearium.com wrote:
> > Hello,
> >
> > I am trying to code a small C program that basically takes a long text
> > file with data that comes from a mysql server.

If you know the exact syntax of the incoming text, you could hand
write a parser. Essentially, you need to know all the states you can
be in.

For e.g.: You cannot encounter a </p> before you a <p>. Etc.

HTH,

Hareesh

PS: But you should use an existing library which Fabrizio mentions,
instead of reinventing the wheel.

> >
> > But I realize It is better to use regular expression. This is an examples
> > of the text:
> >
> > =1 <p> blah </p> <div foo>{$foobar}</div>blah.... <p>linux rulez</p>
> > misc characters.... =2 blah blah <p> linux rulez again</p>....
> > <p>foo</p?blah
> >
> >
> > And so on.
> >
> > The patterns are:
> >
> > The record is represented by an equal. Ej, record 1 is "=1", record 2 is
> > "=2" and so on.
> >
> > The desired text is where "linux rulez" is inside, it is the FIRST <p>
> > </p> AFTER a record.
> >
> > So, I see that program this makes no sense because it is better to use sed
> > and awk.
> >
> > The result I want to have is something like:
> >
> > 1 linux rulez
> > 2 linux rulez again
> > 3 linux rulez so far
> > ...etc
> >
> > The idea is elimate all <div>'s tags, then get the numbers (maybe with awk
> > -F"="), and then get the next <p> taq, remove the tags themself and
> > numbers and then the text and do the same procedure for all the 65230
> > records.
> >
> > Thanks alot for any comment, sorry for the 'offtopic'
> >
> > Kind regards,
> >
> > fabio
> >
> Why don't you use an XML parser library?
> 
> Fabrizio
> -
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Re: Pattern matching programming

[Glynn Clements]

fabio@crearium.com wrote:

> I am trying to code a small C program that basically takes a long text
> file with data that comes from a mysql server.
> 
> But I realize It is better to use regular expression. This is an examples
> of the text:
> 
> =1 <p> blah </p> <div foo>{$foobar}</div>blah.... <p>linux rulez</p>
> misc characters.... =2 blah blah <p> linux rulez again</p>.... <p>foo</p?blah

Don't try to parse anything as complex as HTML/SGML/XML using an
ad-hoc set of rules; use an existing library.

More generally, don't try to perform any non-trivial parsing without
familiarising yourself with the core theoretical concepts behind
formal grammars. A reasonable starting point is:

	http://en.wikipedia.org/wiki/Formal_grammar

If you can't locate an existing library for the language in question,
and you are using C or C++, the appropriate solution is almost
invariably to use lex (or flex) and yacc (or bison) to generate the
parser.

Using an ad-hoc approach (i.e. hand-coding a parser using the
functions in <regex.h> or, worse still, <string.h> or hand-coded
equivalents) is a recipe for producing a parser that is at worst
incorrect (i.e. will produce the wrong result in some cases) and at
best inefficient (it isn't hard to end up with a parser which is a
hundred times slower than an optimal lex-generated one).

-- 
Glynn Clements <glynn@gclements.plus.com>