在c＃中使用Indexof提取字符串

Question

I am trying to extract the number portion in this filename. "Name, lastname_123456_state_city.pdf"

I have got this far..

idstring = file.Substring(file.IndexOf("_") + 1, 
    (file.LastIndexOf("_") - file.IndexOf("_") - 1));

Answer 1

This is one of those cases where a regex might be better:

_(\d+)_

And, here is how you would use it

    string input = "Name, lastname_123456_state_city.pdf";
    string regexPattern = @"_(\d+)_";

Match match = Regex.Match(input, regexPattern, RegexOptions.IgnoreCase);

if (match.Success)
    string yourNumber = match.Groups[1].Value;

Answer 2

var firstUnderscore = file.IndexOf("_");
var nextUnderscore = file.IndexOf("_", firstUnderscore + 1);
var idstring = file.Substring(firstUnderscore + 1, nextUnderscore - firstUnderscore - 1);

Answer 3

Why not just use a regular expression? Testing for @"_([0-9]*)_" should do the trick.

Answer 4

You could use a System.Text.RegularExpressions.Regex

var regex = new Regex(@"^.*_(?<number>\d+)_.*\.pdf");
var idstring=regex.Match(file).Groups["number"].Value;