Tobi One more thing about the way I wish it could work (I remember having done this in C perhaps 30 years ago). The pseudo-code bellow is pretty schematic, but I think it will clarify the issue.
Let p and l be arrays of integers and s be the string "abc defg hijkl" So, after traversing the string we would have the following result: p[0] = offset of "a" (0) l[0] = length of "abc" (3) p[1] = offset of "d" (4) l[1] = lenght of "defg" (4) p[2] = offset of "h" (9) l[2] = lenght of "hijkl" (5). After this, each word could be retrieved in the following manner: for i = 0 to 2 print mid(s, p[i], l[i]) next I think this would be the most efficient way to do it. But I can't find how to do it in Gambas using Regex. Regards - fernando 2017-06-17 18:06 GMT-03:00 Tobias Boege <tabo...@gmail.com>: > On Sat, 17 Jun 2017, Fernando Cabral wrote: > > Still beating my head against the wall due to my lack of knowledge about > > the PCRE methods and properties... Because of this, I have progressed not > > only very slowly but also -- I fell -- in a very inelegant way. So > perhaps > > you guys who are more acquainted with PCRE might be able to hint me on a > > better solution. > > > > I want to search a long string that can contain a sentence, a paragraph > or > > even a full text. I wanna find and isolate every word it contains. A word > > is defined as any sequence of alphabetic characters followed by a > > non-alphatetic character. > > > > The Mathematician in me can't resist to point this out: you hopefully > wanted > to define "word in a string" as "a *longest* sequence of alphabetic > characters > followed by a non-alphabetic character (or the end of the string)". Using > your > definition above, the words in "abc:" would be "c", "bc" and "abc", whereas > you probably only wanted "abc" (the longest of those). > > > The sample code bellow does work, but I don't feel it is as elegant and > as > > fast as it could and should be. Especially the way I am traversing the > > string from the beginning to the end. It looks awkward and slow. There > must > > be a more efficient way, like working only with offsets and lengths > instead > > of copying the string again and again. > > > > You think worse of String.Mid() than it deserves, IMHO. Gambas strings > are triples of a pointer to some data, a start index and a length, and > the built-in string functions take care not to copy a string when it's > not necessary. The plain Mid$() function (dealing with ASCII strings only) > is implemented as a constant-time operation which simply takes your input > string and adjusts the start index and length to give you the requested > portion of the string. The string doesn't even have to be read, much less > copied, to do this. > > Now, the String.Mid() function is somewhat more complicated, because > UTF-8 strings have variable-width characters, which makes it difficult > to map byte indices to character positions. To implement String.Mid(), > your string has to be read, but, again, not copied. > > Extracting a part of a string is a non-destructive operation in Gambas > and no copying takes place. (Concatenating strings, on the other hand, > will copy.) So, there is some reading overhead (if you need UTF-8 strings), > but it's smaller than you probably thought. > > > Dim Alphabetics as string "abc...zyzABC...ZYZ" > > Dim re as RegExp > > Dim matches as String [] > > Dim RawText as String > > > > re.Compile("([" & Alphabetics & "]+?)([^" & Alphabetics & "]+)", > > RegExp.utf8) > > RawText = "abc12345def ghi jklm mno p1" > > > > Do While RawText > > re.Exec(RawText) > > matches.add(re[1].text) > > RawText = String.Mid(RawText, String.Len(re.text) + 1) > > Loop > > > > For i = 0 To matches.Count - 1 > > Print matches[i] > > Next > > > > > > Above code correctly finds "abc, def, ghi, jlkm, mno, p". But the tricks > I > > have used are cumbersome (like advancing with string.mid() and resorting > to > > re[1].text and re.text. > > > > Well, I think you can't use PCRE alone to solve your problem, if you want > to capture a variable number of words in your submatches. I did a bit of > reading and from what I gather [1][2] capturing group numbers are assigned > based on the verbatim regular expression, i.e. the number of submatches > you can receive is limited by the number of "(...)" constructs in your > expression; and the (otherwise very nifty) recursion operator (?R) does > not give you an unlimited number of capturing groups, sadly. > > Anyway, I think by changing your regular expression, you can let PCRE take > care of the string advancement, like so: > > 1 #!/usr/bin/gbs3 > 2 > 3 Use "gb.pcre" > 4 > 5 Public Sub Main() > 6 Dim r As New RegExp > 7 Dim s As string > 8 > 9 r.Compile("([[:alpha:]]+)[[:^alpha:]]+(.*$)", RegExp.UTF8) > 10 s = "abc12345def ghi jklm mno p1" > 11 Print "Subject:";; s > 12 Do > 13 r.Exec(s) > 14 If r.Offset = -1 Then Break > 15 Print " ->";; r[1].Text > 16 s = r[2].Text > 17 Loop While s > 18 End > > Output: > > Subject: abc12345def ghi jklm mno p1 > -> abc > -> def > -> ghi > -> jklm > -> mno > -> p > > But, I think, this is less efficient than using String.Mid(). The trailing > group (.*$) _may_ make the PCRE library read the entire subject every time. > And I believe gb.pcre will copy your submatch string when returning it. > If you care deeply about this, you'll have to trace the code in gb.pcre > and main/gbx (the interpreter) to see what copies strings and what doesn't. > > Regards, > Tobi > > [1] http://www.regular-expressions.info/recursecapture.html (Capturing > Groups Inside Recursion or Subroutine Calls) > [2] http://www.rexegg.com/regex-recursion.html (Groups Contents and > Numbering in Recursive Expressions) > > -- > "There's an old saying: Don't change anything... ever!" -- Mr. Monk > > ------------------------------------------------------------ > ------------------ > Check out the vibrant tech community on one of the world's most > engaging tech sites, Slashdot.org! http://sdm.link/slashdot > _______________________________________________ > Gambas-user mailing list > Gambas-user@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/gambas-user > -- Fernando Cabral Blogue: http://fernandocabral.org Twitter: http://twitter.com/fjcabral e-mail: fernandojosecab...@gmail.com Facebook: f...@fcabral.com.br Telegram: +55 (37) 99988-8868 Wickr ID: fernandocabral WhatsApp: +55 (37) 99988-8868 Skype: fernandojosecabral Telefone fixo: +55 (37) 3521-2183 Telefone celular: +55 (37) 99988-8868 Enquanto houver no mundo uma só pessoa sem casa ou sem alimentos, nenhum político ou cientista poderá se gabar de nada. ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Gambas-user mailing list Gambas-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/gambas-user