Get Index of First non-Whitespace Character in C# String

Question

Is there a means to get the index of the first non-whitespace character in a string (or more generally, the index of the first character matching a condition) in C# without

Answer 1

There is a very simple solution

string test = "    hello world";
int pos = test.ToList<char>().FindIndex(x => char.IsWhiteSpace(x) == false);

pos will be 4

you can have more complex conditions like:

pos = test.ToList<char>().FindIndex((x) =>
                {
                    if (x == 's') //Your complex conditions go here
                        return true;
                    else 
                        return false;
                }
            );

Answer 2

You can use the String.IndexOfAny function which returns the first occurrence any character in a specified array of Unicode characters.

Alternatively, you can use the String.TrimStart function which remove all white space characters from the beginning of the string. The index of the first non-white space character is the difference between the length of the original string and the trimmed one.

You can even pick a set of characters to trim :)

Basically, if you are looking for a limited set of chars (let's say digits) you should go with the first method.

If you are trying to ignore a limited set of characters (like white spaces) you should go with the second method.

A Last method would be to use the Linq methods:

string s = "        qsdmlkqmlsdkm";
Console.WriteLine(s.TrimStart());
Console.WriteLine(s.Length - s.TrimStart().Length);
Console.WriteLine(s.FirstOrDefault(c => !Char.IsWhiteSpace(c)));
Console.WriteLine(s.IndexOf(s.FirstOrDefault(c => !Char.IsWhiteSpace(c))));

Output:

qsdmlkqmlsdkm
8
q
8

Answer 3

Since there were several solutions here I decided to do some performance tests to see how each performs. Decided to share these results for those interested...

    int iterations = 1000000;
    int result = 0;
    string s= "   \t  Test";

    System.Diagnostics.Stopwatch watch = new Stopwatch();

    // Convert to char array and use FindIndex
    watch.Start();
    for (int i = 0; i < iterations; i++)
        result = Array.FindIndex(s.ToCharArray(), x => !char.IsWhiteSpace(x)); 
    watch.Stop();
    Console.WriteLine("Convert to char array and use FindIndex: " + watch.ElapsedMilliseconds);

    // Trim spaces and get index of first character
    watch.Restart();
    for (int i = 0; i < iterations; i++)
        result = s.IndexOf(s.TrimStart().Substring(0,1));
    watch.Stop();
    Console.WriteLine("Trim spaces and get index of first character: " + watch.ElapsedMilliseconds);

    // Use extension method
    watch.Restart();
    for (int i = 0; i < iterations; i++)
        result = s.IndexOf<char>(c => !char.IsWhiteSpace(c));
    watch.Stop();
    Console.WriteLine("Use extension method: " + watch.ElapsedMilliseconds);

    // Loop
    watch.Restart();
    for (int i = 0; i < iterations; i++)
    {   
        result = 0;
        foreach (char c in s)
        {
            if (!char.IsWhiteSpace(c))
                break;
            result++;
        }
    }
    watch.Stop();
    Console.WriteLine("Loop: " + watch.ElapsedMilliseconds);

Results are in milliseconds....

Where s = " \t Test"
Convert to char array and use FindIndex: 154
Trim spaces and get index of first character: 189
Use extension method: 234
Loop: 146

Where s = "Test"
Convert to char array and use FindIndex: 39
Trim spaces and get index of first character: 155
Use extension method: 57
Loop: 15

Where s = (1000 character string with no spaces)
Convert to char array and use FindIndex: 506
Trim spaces and get index of first character: 534
Use extension method: 51
Loop: 15

Where s = (1000 character string that starts with " \t Test")
Convert to char array and use FindIndex: 609
Trim spaces and get index of first character: 1103
Use extension method: 226
Loop: 146

Draw your own conclusions but my conclusion is to use whichever one you like best because the performance differences is insignificant in real world scenerios.

Answer 4

Yes you can try this:

string stg = "   xyz";
int indx = (stg.Length - stg.Trim().Length);  

Answer 5

You can trim, get the first character and use IndexOf.