Help with a regular expression

Question

I am fairly new to regular expressions and have been having difficulty using one to extract the data I am after. Specifically, I am looking to extract the date touched and the the counter from the following:

<span style="color:blue;">&lt;query&gt;</span>
  <span style="color:blue;">&lt;pages&gt;</span>
    <span style="color:blue;">&lt;page pageid=&quot;3420&quot; ns=&quot;0&quot; title=&quot;Test&quot; touched=&quot;2011-07-08T11:00:58Z&quot; lastrevid=&quot;17889&quot; counter=&quot;9&quot; length=&quot;6269&quot; /&gt;</span>
    <span style="color:blue;">&lt;/pages&gt;</span>
  <span style="color:blue;">&lt;/query&gt;</span>
<span style="color:blue;">&lt;/api&gt;</span>

I am currently using vs2010. My current expression is:

std::tr1::regex rx("(?:.*touch.*;)?([0-9-]+?)(?:T.*count.*;)([0-9]+)(&.*)?");
std::tr1::regex_search(buffer, match, rx);

match[1] contains the following:

    2011-07-08T11:00:58Z&quot; lastrevid=&quot;17889&quot; counter=&quot;9&quot; length=&quot;6269&quot; /&gt;</span>
    <span style="color:blue;">&lt;/pages&gt;</span>
  <span style="color:blue;">&lt;/query&gt;</span>
<span style="color:blue;">&lt;/api&gt;</span>

match[2] contains the following:

6269&quot; /&gt;</span>
    <span style="color:blue;">&lt;/pages&gt;</span>
  <span style="color:blue;">&lt;/query&gt;</span>
<span style="color:blue;">&lt;/api&gt;</span>

I am looking for just "2011-07-08" in match[1] and just "9" in match[2]. The date format will never alter, but the counter will almost certainly be much larger.

Any help would be highly appreciated.

Extracting information out of XML documents is much easier (and more maintainable...) with XPath than with regular expressions. — Frerich Raabe, Jul 27 '11 at 13:18
@Artanthos: Isn't HTML? [Regardless, I believe this might apply.](http://stackoverflow.com/questions/1732348/regex-match-open-tags-except-xhtml-self-contained-tags/1732454#1732454) — yarian, Jul 27 '11 at 13:20
Yes, it is HTML. I am scraping usage data off a website and this is what I have available to work with. — Artanthos, Jul 27 '11 at 15:25

Raphaël Saint-Pierre · Accepted Answer · 2011-07-27T14:52:18.660

1

That's because cmatch::operator[](int i) returns a sub_match, whose sub_match::operator basic_string() (used in the context of cout) returns a string starting at the beginning of the match and ending at the end of the source string.

Use sub_match::str(), i.e. match[1].str() and match[2].str().

Moreover, you'll need your expression to be more specific: .* tries to match the world, and gives up some if it can't.

Try std::tr1::regex rx("touched="([0-9-]+).+counter="([0-9]+)");.

You could even use non-greedy matchers (like +? and *?) to prevent excessive matching.

edited Jul 27 '11 at 14:52

answered Jul 27 '11 at 13:40

Raphaël Saint-Pierre

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Is `*` the non-greedy character in TR1 regex? In most other implementations `?` is used. – Platinum Azure Jul 27 '11 at 14:39
Or maybe you want the super-greedy one (`+`)? – Platinum Azure Jul 27 '11 at 14:40
@Platinum: oh, thanks ! I guess I could invoke the brain fart excuse. – Raphaël Saint-Pierre Jul 27 '11 at 14:53
Thank you. `match[2]` now returns a string starting with the "9". While not ideal, I can just cut `match[1]` and `match[2]` down with a something like `scanf(match[2].first, "%d", &count");` – Artanthos Jul 27 '11 at 15:30
@Artanthos: the matcher will not do type conversions for you indeed. You could use `istringstream`, which is less error-prone. If you really want to use `scanf` - or `atoi`, make sure you get a string pointer out of the match (say, you could use `match[2].str().c_str()`). – Raphaël Saint-Pierre Jul 27 '11 at 16:09
@RaphaelSP: No worries, happens to the best of us! – Platinum Azure Jul 27 '11 at 16:22
@Artanthos: oh, by the way, if you think my answer does fulfill your needs, it would be very stackoverflowish of you to accept it :) (see http://meta.stackexchange.com/questions/5234/how-does-accepting-an-answer-work) – Raphaël Saint-Pierre Jul 27 '11 at 17:11
'match[2].first' gives the same data conversion as `match[2].str().c_str()` – Artanthos Jul 27 '11 at 17:28
@Arthanthos: Ah, indeed. The submatch contains `const char *`'s and not fancy iterators. My bad. – Raphaël Saint-Pierre Jul 27 '11 at 18:24

score 0 · Answer 2 · answered Jul 27 '11 at 13:04

0

Try

std::tr1::regex rx("(?:.*touch.*;)?([0-9-]+)(?:T.*count.*;)([0-9]+)(&.*)?");

removing the question mark makes the term greedy, so it will fill as much as it can.

answered Jul 27 '11 at 13:04

marc

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Help with a regular expression

2 Answers2