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

string result = Regex.Match(source, @"q\s*=\s*(?<value>[0-9]+)").Groups["value"].Value; — Dmitrii Bychenko
– Dmitrii Bychenko, Commented Nov 6, 2019 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 — Crowcoder
– Crowcoder, Commented Nov 6, 2019 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
– Zohar Peled, Commented Nov 6, 2019 at 12:37

Matthew Watson · Accepted Answer · 2019-11-06 12:38:49Z

10

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"]);

answered Nov 6, 2019 at 12:38

Matthew Watson

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1 Comment

Sinatr Over a year ago

Canonical duplicate.

Linerath · Accepted Answer · 2019-11-06 12:37:56Z

1

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
}

answered Nov 6, 2019 at 12:37

Linerath

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Comments

NotFound · Accepted Answer · 2019-11-06 12:40:14Z

1

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);

answered Nov 6, 2019 at 12:40

NotFound

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Comments

Tim Rutter · Accepted Answer · 2019-11-06 12:43:12Z

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 6, 2019 at 12:43

Tim Rutter

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