Convert cm to mm using Regex.Replace()

Question

I want to take the following input <tag>30.234234cm</tag> and get the following output <tag>302.34234mm</tag> . Where the value between the tags is a value in centimetres that may be decimal or integer, and the goal is to convert that value to millimetres.

var input = "<tag>30.234234cm</tag>";
input = Regex.Replace(input, @"(\d+(\.\d+)?)cm", (double.Parse("$1") * 10).ToString() + 
    "mm", RegexOptions.IgnoreCase);

I am using the expression (\\d+(\\.\\d+)?) for the first capture group. However, $1 will not work in the context of double.Parse($1) . How can I get the value of the unit, convert it and replace it in the example string provided?

Answer 1

Well,

  double.Parse("$1")

tries to parse "$1" constant string and fails. I suggest using lambda :

  var input = "<tag>30.234234cm</tag>";

  input = Regex.Replace(
      input, 
     @"(\d+(\.\d+)?)cm", 
      match => (double.Parse(match.Groups[1].Value) * 10).ToString() + "mm",
      RegexOptions.IgnoreCase);

Here match.Groups[1].Value is a value of the captured group ( 30.234234 in the example)

Answer 2

你使用"(\\d+(\\.\\d+)?)cm"和“cm”作为捕获，因为你不能执行`double.Parse（“$ 1”）