ColdFusion REFind() Cannot Find The Empty String

When you step back and think about it, this makes perfect sense; but, yesterday, for a few minutes, I was completely stumped as to why my ColdFusion REFind() method call was not working. I was using regular expressions to validate strings and for strings that could be zero or more characters, I was using a regular expression that looked like this:

^.{0,50}$

It worked for strings that had positive lengths, but failed for zero length strings:

Running the above code gives us the following output:

Not Found!

If you run this in any kind of third-party regular expression tester, like The RegEx Coach, it will work fine. The problem is not in the regular expression. In fact, there really is no problem at all. The reason this doesn't work is that it cannot co-exist with the one-based indexing used in ColdFusion. The REFind() and REFindNoCase() functions return "the position in the string where the match begins;" since ColdFusion strings begin at index one, it is impossible to return the a match that has no length as it will also have no index. In other words, for the REFind() method to match the empty string it would have to also confirm that the target string has a length, which would be a contradiction.

In order to get this to work, I had to switch over to using the Java Pattern object's Matches() method:

This time, when we run the code above we get the following output:

Found!

As you can see, the Java Pattern object was able to match the empty string.

Now, just to make sure that I was really on the right track, I tested to see if the REReplace() method, which doesn't care about string indexes, would match the empty string:

When we run this code, we get the following output:

Replaced!

That works just fine. So, like I said, when you step back and think about what the ColdFusion REFind() and REFindNoCase() methods actually do, it becomes obvious that they cannot match the empty string. But, when you have your nose deep in code, sometimes it's not that obvious.

And, as one more test, I just wanted to see if ColdFusion 8's new REMatch() function could match the empty string:

When we run this, we get the following output:

Index 1: []

As you can see, ColdFusion's REMatch() does successfully match and return the empty string.

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