Why Regex Count works as Length in C#?

Question

I was looking for an answer for "how to count the occurrence of a substring in the desired string in c# using Regex?". There are many references like here to use "Count" as following:

int count = Regex.Match(MyString, "OU=").Count

I tried to use it but every time in c# there was an error message and a suggestion to use ".Length".

Eventually, I did it using the following code snippet.

    private int GetCounts(string source, string substring)
    {
        int iCount = 0;
        foreach (Match match in Regex.Matches(source, substring))
            iCount++;
        return iCount;
    }

Could anybody explain why ".Count" is not working as expected? Answers appreciated in advance.

Hi. Welcome to [so]. Help us help you. Can you please provide at least a sample test, tell how it does not match your requirements. Ideally provide a [mcve]. — PJProudhon, May 16 '19 at 13:59
are you using a framework version below 4.8 ? Because this property exists and I can compile your first line of code without problems. Here is [the documentation](https://learn.microsoft.com/en-us/dotnet/api/system.text.regularexpressions.matchcollection.count?view=netframework-4.8) — Mong Zhu, May 16 '19 at 14:01
@MongZhu `MatchCollection.Count` has been available since 1.1 — canton7, May 16 '19 at 14:03
@canton7 haha thank you, I was looking at the wrong place for the version. stupid :D — Mong Zhu, May 16 '19 at 14:04
Please show your RegEx and the string leading to the error. The only reason why `.Count` would fail (that is, with a `RegexMatchTimeoutException`) is when the RegEx evaluation takes to long, indicating an incorrect RegEx. — Thomas Flinkow, May 16 '19 at 14:06
@ThomasFlinkow He said "*I tried to use it but every time in c# there was an error message and a suggestion to use ".Length".*", indicating that it's not a problem with a timeout, but instead it's a compile-time error. Also he did show us his Regex string: `"OU="` — canton7, May 16 '19 at 14:07
@canton7 Yes. Exactly. More interestingly somebody voted down the question when you guys are trying to help. Thanks to all you, guys.:-) — amirfg, May 16 '19 at 14:10
@amirfg It's being downvoted because we cannot reproduce it. The code you gave us does not cause the error you say it causes. That makes it a bad question. — canton7, May 16 '19 at 14:11
I took the liberty and changed the code to make the problem reproducible — Mong Zhu, May 16 '19 at 14:35

Thomas Flinkow · Accepted Answer · 2019-05-16T14:16:33.633

4

You likely used Regex.Match when you should have used Regex.Matches.

The first returns a Match, which only has a Length property, while the latter returns a MatchCollection only having a Count property.

edited May 16 '19 at 14:16

answered May 16 '19 at 14:14

Thomas Flinkow

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(@amirfg This is why it's important that your question is correct. Please always make sure that the code in your question is actually the code you're trying to run) – canton7 May 16 '19 at 14:16

Why Regex Count works as Length in C#?

1 Answers1