175

I'm trying to figure out the best way to get everything before the - character in a string. Some example strings are below. The length of the string before - varies and can be any length

223232-1.jpg
443-2.jpg
34443553-5.jpg

so I need the value that's from the start index of 0 to right before -. So the substrings would turn out to be 223232, 443, and 34443553

one noa
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PositiveGuy
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9 Answers9

186

.Net Fiddle example

class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine("223232-1.jpg".GetUntilOrEmpty());
        Console.WriteLine("443-2.jpg".GetUntilOrEmpty());
        Console.WriteLine("34443553-5.jpg".GetUntilOrEmpty());

        Console.ReadKey();
    }
}

static class Helper
{
    public static string GetUntilOrEmpty(this string text, string stopAt = "-")
    {
        if (!String.IsNullOrWhiteSpace(text))
        {
            int charLocation = text.IndexOf(stopAt, StringComparison.Ordinal);

            if (charLocation > 0)
            {
                return text.Substring(0, charLocation);
            }
        }

        return String.Empty;
    }
}

Results:

223232
443
34443553
344

34
Demodave
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Fredou
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    Please do them a favor and add error checking as well assuming he plans to make a function out of this :) – Josh Dec 07 '09 at 02:51
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    If you wanted a one-liner without losing proper "not found" checking then you could do something like this: `string result = source.Substring(0, Math.Max(source.IndexOf('-'), 0))` – LukeH Dec 07 '09 at 09:58
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    Instead of `s.Substring(0, n)` one can use `s.Remove(n)` when it is known (like here) that the length of the string `s` strictly exceeds `n`. – Jeppe Stig Nielsen Nov 27 '14 at 12:45
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    @LukeH If IndexOf returns -1 in your example, then an empty string would be returned, wouldn't it? – crush Jun 25 '15 at 14:35
  • @crush: Yes. My example is simply a single-line equivalent of Fredou's answer, so it returns an empty string when no `-` character is found. – LukeH Jun 26 '15 at 00:08
  • int l = s.IndexOf("-", StringComparison.Ordinal); – Kurkula Oct 07 '16 at 22:27
  • Sample also doesn't work if the '-' is the first character of the string. Should use >= instead of >. – sjb-sjb May 30 '18 at 11:00
  • This answer is poor because it doesn't explain any of the code here. Please edit it to include an explanation of what the relevant functions are here and how they work. – TylerH Jun 08 '22 at 22:16
174

Use the split function. 

static void Main(string[] args)
{
    string s = "223232-1.jpg";
    Console.WriteLine(s.Split('-')[0]);
    s = "443-2.jpg";
    Console.WriteLine(s.Split('-')[0]);
    s = "34443553-5.jpg";
    Console.WriteLine(s.Split('-')[0]);

Console.ReadKey();
}

If your string doesn't have a - then you'll get the whole string.

Dominic Cronin
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    And if you have more than one hyphen, you get multiple elements in your array. – James Dunne Nov 12 '12 at 15:48
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    Indeed, James, so this would only be a solution if you expected only a single hyphen. I suppose you could use Linq methods like skip and aggregate to get what you wanted, but then you've got more code than the methods that have been proposed already. It all depends on how much you know about the incoming data. – Dominic Cronin Nov 12 '12 at 19:50
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    And a few years on, I have just realised that I was rather too quick to concede James's point. The question asks how to find the string before a certain character. Further instances of that character are thus irrelevant, and taking [0] would "just work". Of course, it still depends on how much we trust the incoming data. What if there's no '-' at all? – Dominic Cronin May 26 '15 at 11:43
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    I think @JamesDunne point was that by splitting into an array, you're creating a bunch of unnecessary strings - unnecessary garbage. – crush Jun 25 '15 at 14:28
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    I wouldn't worry about "unnecessary garbage". Any extra strings created this way would be immediately unreachable and therefore collected in generation 0, which is an extremely low overhead indeed. The garbage collector design is explicitly intended to allow for large numbers of short-lived items to be used with almost no expense. – Dominic Cronin Oct 05 '15 at 18:07
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    +1 Important to note for rookies (as myself) that: [0] is everything split to the left and [1] is everything split to the right of the character being split from....at least that is what I deduced when substituting 0 for 1 in the index. – J.S. Orris Oct 15 '15 at 19:19
  • Jeff, if you have more than one hyphen, you get a longer array. Follow the hyperlink in my answer to see the docs – Dominic Cronin Oct 15 '15 at 19:51
  • I don't see how this works since `.Split()` works on `String[]`, not `String`. – TylerH Jun 08 '22 at 22:28
  • The very first line of my answer links to the documentation for this function: http://msdn.microsoft.com/en-us/library/system.string.split.aspx – Dominic Cronin Jun 10 '22 at 10:49
  • Wow! Got a drive-by downvote yesterday (the only one). Whoever it was didn't have the courtesy to comment on what they thought was poor. – Dominic Cronin Aug 30 '23 at 10:48
79
String str = "223232-1.jpg"
int index = str.IndexOf('-');
if(index > 0) {
    return str.Substring(0, index)
}
BrainCore
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12

Things have moved on a bit since this thread started.

Now, you could use

string.Concat(s.TakeWhile((c) => c != '-'));
Anthony Wieser
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  • How does this compare performance wise to the obvious IndexOf and Substring combination? I assume it is appending each character to a StringBuilder, and then producing a string at the end. There's also a couple of function calls mixed in. Would've been nice if Substring could simply take -1 as a "length" argument meaning "end of string". – crush Jun 25 '15 at 14:23
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    It's worse for efficiency. As you say, it uses a string builder, and having inspected the code appears to call ToString on each character. It is clearer if you're looking for more than one character, as you could rewrite the lambda easily. – Anthony Wieser Jun 27 '15 at 06:15
8

One way to do this is to use String.Substring together with String.IndexOf:

int index = str.IndexOf('-');
string sub;
if (index >= 0)
{
    sub = str.Substring(0, index);
}
else
{
    sub = ... // handle strings without the dash
}

Starting at position 0, return all text up to, but not including, the dash.

Michael Petrotta
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8

Slightly modified and refreshed Fredou's solution for C# ≥ 8

/// <summary>
/// Get substring until first occurrence of given character has been found. Returns the whole string if character has not been found.
/// </summary>
public static string GetUntil(this string that, char @char)
{
    return that[..(IndexOf() == -1 ? that.Length : IndexOf())];
    int IndexOf() => that.IndexOf(@char);
}

Tests:

[TestCase("", ' ', ExpectedResult = "")]
[TestCase("a", 'a', ExpectedResult = "")]
[TestCase("a", ' ', ExpectedResult = "a")]
[TestCase(" ", ' ', ExpectedResult = "")]
[TestCase("/", '/', ExpectedResult = "")]
[TestCase("223232-1.jpg", '-', ExpectedResult = "223232")]
[TestCase("443-2.jpg", '-', ExpectedResult = "443")]
[TestCase("34443553-5.jpg", '-', ExpectedResult = "34443553")]
[TestCase("34443553-5-6.jpg", '-', ExpectedResult = "34443553")]
public string GetUntil(string input, char until) => input.GetUntil(until);
Dariusz Woźniak
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2

The LINQy way

String.Concat( "223232-1.jpg".TakeWhile(c => c != '-') )

(But, you do need to test for null ;)

Den
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1

Building on BrainCore's answer:

    int index = 0;   
    str = "223232-1.jpg";

    //Assuming we trust str isn't null 
    if (str.Contains('-') == "true")
    {
      int index = str.IndexOf('-');
    }

    if(index > 0) {
        return str.Substring(0, index);
    }
    else {
       return str;
    }
n122vu
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0

You can use regular expressions for this purpose, but it's good to avoid extra exceptions when input string mismatches against regular expression.

First to avoid extra headache of escaping to regex pattern - we could just use function for that purpose:

String reStrEnding = Regex.Escape("-");

I know that this does not do anything - as "-" is the same as Regex.Escape("=") == "=", but it will make difference for example if character is @"\".

Then we need to match from begging of the string to string ending, or alternately if ending is not found - then match nothing. (Empty string)

Regex re = new Regex("^(.*?)" + reStrEnding);

If your application is performance critical - then separate line for new Regex, if not - you can have everything in one line.

And finally match against string and extract matched pattern:

String matched = re.Match(str).Groups[1].ToString();

And after that you can either write separate function, like it was done in another answer, or write inline lambda function. I've wrote now using both notations - inline lambda function (does not allow default parameter) or separate function call.

using System;
using System.Text.RegularExpressions;

static class Helper
{
    public static string GetUntilOrEmpty(this string text, string stopAt = "-")
    {
        return new Regex("^(.*?)" + Regex.Escape(stopAt)).Match(text).Groups[1].Value;
    }
}

class Program
{
    static void Main(string[] args)
    {
        Regex re = new Regex("^(.*?)-");
        Func<String, String> untilSlash = (s) => { return re.Match(s).Groups[1].ToString(); };

        Console.WriteLine(untilSlash("223232-1.jpg"));
        Console.WriteLine(untilSlash("443-2.jpg"));
        Console.WriteLine(untilSlash("34443553-5.jpg"));
        Console.WriteLine(untilSlash("noEnding(will result in empty string)"));
        Console.WriteLine(untilSlash(""));
        // Throws exception: Console.WriteLine(untilSlash(null));

        Console.WriteLine("443-2.jpg".GetUntilOrEmpty());
    }
}

Btw - changing regex pattern to "^(.*?)(-|$)" will allow to pick up either until "-" pattern or if pattern was not found - pick up everything until end of string.

TarmoPikaro
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