Regex for numbers only

c# regex
Timothy Carter picture Timothy Carter · Nov 7, 2008 · Viewed 876.8k times · Source

I haven't used regular expressions at all, so I'm having difficulty troubleshooting. I want the regex to match only when the contained string is all numbers; but with the two examples below it is matching a string that contains all numbers plus an equals sign like "1234=4321". I'm sure there's a way to change this behavior, but as I said, I've never really done much with regular expressions.

string compare = "1234=4321";
Regex regex = new Regex(@"[\d]");

if (regex.IsMatch(compare))
{ 
    //true
}

regex = new Regex("[0-9]");

if (regex.IsMatch(compare))
{ 
    //true
}

In case it matters, I'm using C# and .NET2.0.

Answer

Bill the Lizard picture Bill the Lizard · Nov 7, 2008

Use the beginning and end anchors.

Regex regex = new Regex(@"^\d$");

Use "^\d+$" if you need to match more than one digit.

Note that "\d" will match [0-9] and other digit characters like the Eastern Arabic numerals ٠١٢٣٤٥٦٧٨٩. Use "^[0-9]+$" to restrict matches to just the Arabic numerals 0 - 9.

If you need to include any numeric representations other than just digits (like decimal values for starters), then see @tchrist's comprehensive guide to parsing numbers with regular expressions.

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