如何计算正则表达式的匹配次数？

Question

例如，我想使用正则表达式计算一个字符串中有多少个数字：[0-9]

Answer 1

Regex.Matches(text, pattern).Count

Answer 2

Regex.Matches(input, @"\d").Count

Since this is going to allocate a Match instance for each match, this may be sub-optimal performance-wise. My instinct would be to do something like the following:

input.Count(Char.IsDigit)

Answer 3

        var a = new Regex("[0-9]");
        Console.WriteLine(a.Matches("1234").Count);
        Console.ReadKey();

Answer 4

The MatchCollection instance returned from a call to the Matches method on RegEx will give you the count of the number of matches.

However, what I suspect is that it might not be the count that is wrong, but you might need to be more specific with your regular expression (make it less greedy) in order to determine the specific instances of the match you want.

What you have now should give you all instances of a single number in a string, so are you getting a result that you believe is incorrect? If so, can you provide the string and the regex?

Answer 5

var regex = new Regex(@"\d+");
var input = "123 456";
Console.WriteLine(regex.Matches(input).Count); // 2
// we want to count the numbers, not the number of digits