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Re: use of "match-string"

From: ken
Subject: Re: use of "match-string"
Date: Tue, 08 Mar 2011 18:48:36 -0500
User-agent: Thunderbird (X11/20101213)

Thanks, Tim.  PJ pointed this out a couple hours before you.  You were
quick, but he was quicker.

On 03/08/2011 04:36 PM Tim X wrote:
> ken <address@hidden> writes:
>> Part of this function doesn't make sense--
>> (defun html-toc-find-max ()
>>   (goto-char (point-min))
>>   (let ((max-toc 0))
>>     (while (search-forward-regexp html-toc-tocref nil t)
>>       (if (> (string-to-int (match-string 1)) max-toc)
>>           (setq max-toc (string-to-int (match-string 1)))))
>>     (1+ max-toc)))
>> -- specifically, where match-string is first called and turned into a
>> number.  The docs say that match-string returns a string....  Yes, this
>> can be done I suppose, but to what end?  Moreover, depending upon its
>> value, this "number" may then be assigned to a variable, and that value
>> then compared with subsequent strings.
>> Perhaps I'm missing some nuance here.  The entirety of the code is
>> below.  Does anyone understand what's going on here?
> I'm not sure what it is you find 'odd' about the above function. Apart
> from the fact it should be using string-to-number (string-to-int has
> been marked obsolete since 22.1), it seems reasonable to me. 
> The regexp used in the match is 
>> (defvar html-toc-tocref     (concat "<A NAME=\"" html-toc-name-pre
>>                                     "\\([0-9]*\\)\">"))
> Note the 1st (and only) grouping in the regexp i.e. \\([0-9]*\\), which
> will match on 0 or more digits between 0..9. This is what (match-string
> 1) will return. (though as it is [0-9]* it could return 0 or more
> digits, so match-string 1 could be "", which may be an issue).
> The string-to-int call will return that value as a number rather than as
> a string, which is then compared to max-toc (initially set to 0), not to
> a string. The final value has 1 added to it. So, your not comparing
> strings, you are comparing strings of numers that are converted to be a 
> number.
> So, this function would search through the buffer for the specified
> regexp, extract the group of digits as a string, convert them to a
> number and compare them to the last one found. If the number is larger,
> it would set that as the max and then continue the loop. Finally, it
> adds 1. 
> I can see some things I would do differently and even if you don't find
> a match, your max-toc value will have a value of at least 1, but apart
> from that, it seems to do whatever it was intended to do. 
> Tim

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