how to substring from a string using c#?

string format 开发者_运维百科is always like this "FirstName=ABC;LastName=XZY;Username=User1;Password=1234".

I need the only UserName value (which is 'User1' in this case). I wanna achieve this in minimum line of code using substring method (or something else).

Help?

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For the sake of completeness, here is the Regex way of doing it. This will also work if the order changes.

// using System.Text.RegularExpressions;

string test1 = "FirstName=ABC;LastName=XZY;Username=User1;Password=1234";
string test2 = "FirstName=ABC;LastName=XZY;Password=1234;Username=User1";
string test3 = "FirstName=ABC;LastName=XZY;Password=1234";

string regexPattern = @"(?<=Username=)[^;\n]*";
var userName1 = Regex.Match(test1, regexPattern).Value; // User1
var userName2 = Regex.Match(test2, regexPattern).Value; // User1
var userName3 = Regex.Match(test3, regexPattern).Value; // string.Empty

// Compiling can speed up the Regex, at the expense of longer initial Initialization
// Use when this is called often, but measure.

Regex compiledRx = new Regex(regexPattern,RegexOptions.Compiled);
var userNameCompiled1 = compiledRx.Match(test1).Value; // User1
var userNameCompiled2 = compiledRx.Match(test2).Value; // User1
var userNameCompiled3 = compiledRx.Match(test3).Value; // string.Empty

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Looks like a delimited string, so this would work:

string result = myString.Split(';')[2].Split('=')[1];

However, if someone changes the value pair order, this will break.

There are better ways about this, that will not break if the order changes, the number of parameters is different etc - such as the Regular Expression as Michael posted, or the Linq queries posted by a number of people.

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Here is an alternative solution (not too different from others, but which I think is more straightforward) which will work regardless of order.

var input = "FirstName=ABC;LastName=XZY;Username=User1;Password=1234";

Assert.AreEqual("User1", input
    .Split(';')
    .Select(item => item.Split('='))
    .Where(pair => pair[0].Equals("Username"))
    .Single()[1]);

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This method will work even if the value-pairs are given in a different order. It splits on the semicolon, finds the item with "Username", then returns what's after the equal sign.

string theString = "FirstName=ABC;LastName=XZY;Username=User1;Password=1234";
string username = theString.Split(";").Where(s => s.Split("=")[0].Equals("Username")).ToArray()[0].Split("=")[1];

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Least number of lines of code is not always the best metric, but you could do what you need with Regex.

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While the split answers are 'ok' if nothing ever changes, it's probably better to use a function because:

• It makes your intentions clear.
• It is easier to document.
• It is easier to modify should the inevitable happen.
• Works regardless of order.

(Even if you just put the one line split in the function! or at the very least add a comment to the split.)

static String GetUsername(String value)
{
    String result = "";
    String token = "Username=";

    int index = value.IndexOf(token) + token.Length;
    while (value[index] != ';')
    {
        result += value[index++];
        if (index > value.Length - 1)
            break;
    }

    return result;
}

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Not as simple as using split, however:

string input = "FirstName=ABC;LastName=XZY;Username=User1;Password=1234";
string username = Regex.Match(input, "Username=(?<username>.*?)(;|$)").Groups["username"].Value;

In this case, groups can be in any order.

And, if you like to get creative:

var answers = from tuple in input.Split(';')
              where tuple.StartsWith("Username=")
              select tuple.Split('=')[1];

username = answers.Count() > 0 ? answers.First() : string.Empty;

One might say the last piece has better semantics.

EDIT: Update the last piece to deal with input strings that doesn't have the required tuple.

---

        string t = "FirstName=ABC;LastName=XZY;Username=User1;Password=1234";
        string name = t.Split(';')[2].Split('=')[1];

---

This isn't the shortest... but probably one of the fastest.

string value = "FirstName=ABC;LastName=XZY;Username=User1;Password=1234";
int offset = value.IndexOf("Username=") + 9;
if (offset < 9)
    throw new Exception("Username= not found in string");
int len = value.IndexOf(';', offset) - offset;
if (len < 0)
    len = value.Length - offset;
string find = value.Substring(offset, len);

... the if (len < 0) is for is the Username is at the end of the string and doesn't end with a semicolon. If you want to ignore case you can replace the int offset line with this...

int offset = value.ToUpperInvariant().IndexOf("USERNAME=") + 9;