Very Stupid Regex question

[H. S. Teoh via Digitalmars-d-learn]

On Thu, Aug 07, 2014 at 04:49:05PM +0000, seany via Digitalmars-d-learn wrote:
> On Thursday, 7 August 2014 at 16:12:59 UTC, Justin Whear wrote:
> >On Thu, 07 Aug 2014 16:05:16 +0000, seany wrote:
> >
> >>obviously there are ways like counting the match length, and then
> >>using the maximum length, instead of breaking as soon as a match is
> >>found.
> >>
> >>Are there any other better ways?
> >
> >You're not really using regexes properly.  You want to greedily match
> >as much as possible in this case, e.g.:
> >
> >void main()
> >{
> >	import std.regex;
> >	auto re = regex("ab(cd)?");
> >	assert("PREabcdPOST".matchFirst(re).hit == "abcd");
> >	assert("PREabPOST".matchFirst(re).hit == "ab");
> >
> >}
> 
> thing is, abcd is read from a file, and in the compile time, i dont
> know if cd may at all be there or not, ir if it should be ab(ef)

So basically you have a file containing regex patterns, and you want to
find the longest match among them?

One way to do this is to combine them at runtime:

	string[] patterns = ... /* read from file, etc. */;

	// Longer patterns match first
	patterns.sort!((a,b) => a.length > b.length);

	// Build regex
	string regexStr = "%((%(%c%))%||%)".format(patterns);
	auto re = regex(regexStr);

	...

	// Run matches against input
	char[] input = ...;
	auto m = input.match(re);
	auto matchedString = m.captures[0];


T

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