CODEWITHSUNDEEP
c#regexmatch
CodeMonkey
CodeMonkey

Reputation: 12424

C# regex match behaviour

I've got this line in my code:

Match match = Regex.Match(actualValue, regexValue, RegexOptions.None);

I've got a simple question. why when checking for success meaning with the line:

if(match.Success)

then the match does succeed with the following values:

actualValue = "G:1"

regexValue = "A*"

the actual does not seem to fit at least for me so i probably miss something...

what i do want to achieve is just receiving an actual value and a regular expression and check if the actual value fits the regular expression.. i thought that's what i did there but apparently i didn't.

EDIT: another question. is there a way to treat the * as the "any char" wildcard? meaning is it possible that A* will be considered as A and after it any char is possible?

Upvotes: 0

Views: 331

Answers (4)

Chris
Chris

Reputation: 4671

Your code itself is correct; your regular expression isn't.

Based on your comments on other answers, you're after a regular expression which matches any string which starts with A, and you're assuming that '*' means "any characters". '*' in fact means "match the preceding character zero or more times", so the regular expression you've given means "match the start of the string followed by zero or more 'A' characters", which will match absolutely anything.

If you're looking for a regular expression that matches the whole string but only if it starts with 'A', the regular expression you're after is ^A.*. The '.' character in a regular expression means "match any character". This regular expression thus means "match the start of the string, followed by an 'A', followed by zero or more other characters" and will thus match the entire string provided it starts with 'A'.

However, you already have the whole string, so this is a little unnecessary - all you really want to do is get an answer to the question "does the string start with an 'A'?". A regular expression that will achieve this is simply '^A'. If it matches, the string started with an 'A'.

Of course, it should be pointed out that you don't need a regular expression to confirm this anyway. If this is genuinely all you want to do (and it's possible you've just put together a simple example, and your real scenario is more complicated), why not just use the StartsWith method?:

bool match = actualValue.StartsWith("A");

Upvotes: 3

Boris
Boris

Reputation: 532

Looking at the comments it looks like you're trying to match a lot of strings starting with A. If they're separated by white space you could find all of them using the following:

bool matched = Regex.IsMatch(actualValue, @"\bA\w+");

This matches : "Atest flkjs Apple Ascii cAse".

If there is only one string you're matching and it starts with A and has no spaces:

bool matched = Regex.IsMatch(actualValue, @"^A\w+$");

This matches "Apple", but not "Apple and orange" as the second string has spaces.

As Chris noted * is not a wildcard in the way you meant with regex searches. You can find some information to get you started with regexes at regex-info.

Upvotes: 1

Jonas W
Jonas W

Reputation: 3250

Regex take the regular expression in the constructor. Exampel in your case could be :

if(new Regex("A*").IsMatch(actualValue)
   //Do something

If you are unsecure of the regexpattern, try it out here

Upvotes: 0

waldrumpus
waldrumpus

Reputation: 2590

The regex matches because A* means "look for 0 or more occurrences of 'A'". It will match any string.

If you meant to look for an arbitrary number of 'A', but at least one, try A+ instead.

Upvotes: 1

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