Check if a string contains one of 10 characters

Question

I\'m using C# and I want to check if a string contains one of ten characters, *, &, # etc etc.

What is the best way?

Answer 1

As others have said, use IndexOfAny. However, I'd use it in this way:

private static readonly char[] Punctuation = "*&#...".ToCharArray();

public static bool ContainsPunctuation(string text)
{
    return text.IndexOfAny(Punctuation) >= 0;
}

That way you don't end up creating a new array on each call. The string is also easier to scan than a series of character literals, IMO.

Of course if you're only going to use this once, so the wasted creation isn't a problem, you could either use:

private const string Punctuation = "*&#...";

public static bool ContainsPunctuation(string text)
{
    return text.IndexOfAny(Punctuation.ToCharArray()) >= 0;
}

or

public static bool ContainsPunctuation(string text)
{
    return text.IndexOfAny("*&#...".ToCharArray()) >= 0;
}

It really depends on which you find more readable, whether you want to use the punctuation characters elsewhere, and how often the method is going to be called.

---

EDIT: Here's an alternative to Reed Copsey's method for finding out if a string contains exactly one of the characters.

private static readonly HashSet Punctuation = new HashSet("*&#...");

public static bool ContainsOnePunctuationMark(string text)
{
    bool seenOne = false;

    foreach (char c in text)
    {
        // TODO: Experiment to see whether HashSet is really faster than
        // Array.Contains. If all the punctuation is ASCII, there are other
        // alternatives...
        if (Punctuation.Contains(c))
        {
            if (seenOne)
            {
                return false; // This is the second punctuation character
            }
            seenOne = true;
        }
    }
    return seenOne;
}