How can I pick out a number from a string in C#

Question

I have this string:

http://www.edrdg.org/jmdictdb/cgi-bin/edform.py?svc=jmdict&amp;sid=&amp;q=1007040&amp;a=2

How can I pick out the number between "q=" and "&amp" as an integer?

So in this case I want to get the number: 1007040

https://stackoverflow.com/questions/4734116/find-and-extract-a-number-from-a-string — Avid Programmer, Nov 06 '19 at 12:32
`string result = Regex.Match(source, @"q\s*=\s*(?[0-9]+)").Groups["value"].Value;` — Dmitry Bychenko, Nov 06 '19 at 12:35
I wouldn't look at it like getting a number from a string, instead I'd look at it like [parsing a query string](https://stackoverflow.com/questions/11956948/easiest-way-to-parse-querystring-formatted-data) — Crowcoder, Nov 06 '19 at 12:35
This is a URI. Don't attempt to parse it manually. Instead, use the framework's built in tools to do that. — Zohar Peled, Nov 06 '19 at 12:37

score 10 · Accepted Answer · answered Nov 06 '19 at 12:38

What you're actually doing is parsing a URI - so you can use the .Net library to do this properly as follows:

var str   = "http://www.edrdg.org/jmdictdb/cgi-bin/edform.py?svc=jmdict&amp;sid=&amp;q=1007040&amp;a=2";
var uri   = new Uri(str);
var query = uri.Query;
var dict  = System.Web.HttpUtility.ParseQueryString(query);

Console.WriteLine(dict["amp;q"]); // Outputs 1007040

If you want the numeric string as an integer then you'd need to parse it:

int number = int.Parse(dict["amp;q"]);

Canonical [duplicate](https://stackoverflow.com/q/659887/1997232). — Sinatr, Nov 06 '19 at 12:42

score 1 · Answer 2 · answered Nov 06 '19 at 12:37

Consider using regular expressions

String str = "http://www.edrdg.org/jmdictdb/cgi-bin/edform.py?svc=jmdict&amp;sid=&amp;q=1007040&amp;a=2";

Match match = Regex.Match(str, @"q=\d+&amp");

if (match.Success)
{
    string resultStr = match.Value.Replace("q=", String.Empty).Replace("&amp", String.Empty);
    int.TryParse(resultStr, out int result); // result = 1007040
}

score 1 · Answer 3 · answered Nov 06 '19 at 12:40

Seems like you want a query parameter for a uri that's html encoded. You could do:

Uri uri = new Uri(HttpUtility.HtmlDecode("http://www.edrdg.org/jmdictdb/cgi-bin/edform.py?svc=jmdict&amp;sid=&amp;q=1007040&amp;a=2"));
string q = HttpUtility.ParseQueryString(uri.Query).Get("q");
int qint = int.Parse(q);

score 1 · Answer 4 · answered Nov 06 '19 at 12:43

1

A regex approach using groups:

public int GetInt(string str)
{
    var match = Regex.Match(str,@"q=(\d*)&amp");
    return int.Parse(match.Groups[1].Value);
}

Absolutely no error checking in that!

answered Nov 06 '19 at 12:43

Tim Rutter

4,314
2
21
43

How can I pick out a number from a string in C#

4 Answers4