char Array for if String IndexOf String LastIndexOf

`IndexOfAny`

This C# method searches a string for many values. It returns the first position of any of the values you provide (or -1).

Several overloads of the IndexOfAny method are available in .NET. This method is useful in certain C# programs—its performance is not great.

Some examples

IndexOfAny is an instance method that returns an integer value type indicating the position of the found character, or the special value -1 if no value was found.

And The first argument is a character array, which you can declare directly in the parameter list or separately as a variable.

Tip It is sometimes faster to store this char array separately and reuse it whenever calling IndexOfAny.

Detail The IndexOfAny method is called and searches for the lowercase "c" and uppercase "Z" in the 2 input strings.

using System;

// Input.
const string value1 = "abc";
const string value2 = "XYZ";

// Find first location of "c" or "Z."
int index1 = value1.IndexOfAny(new char[] { 'c', 'Z' });
Console.WriteLine(index1);

// Repeat on another string.
int index2 = value2.IndexOfAny(new char[] { 'c', 'Z' });
Console.WriteLine(index2);2
2

`IndexOfAny` benchmark

Consider now the performance of IndexOfAny. Can this method be used in performance-critical string methods? We test its performance.

Version 1 Use IndexOfAny with a new char array allocation as the argument, and test the result.

Version 2 Use a custom for-loop with an if-statement and several conditions in the logic.

Result The IndexOfAny method seems to perform much worse than a for-loop with an if-statement. For a simple search, it is far slower.

However If an array of characters is needed, the IndexOfAny method's performance will likely be more competitive.

using System;
using System.Diagnostics;

const int _max = 1000000;
string test = "abcdefg";
// Version 1: test IndexOfAny.
var s1 = Stopwatch.StartNew();
for (int i = 0; i < _max; i++)
{
    int result = test.IndexOfAny(new char[] { 'd', 'x', '?' });
    if (result != 3)
    {
        return;
    }
}
s1.Stop();
// Version 2: test custom loop with if-statement.
var s2 = Stopwatch.StartNew();
for (int i = 0; i < _max; i++)
{
    int result = -1;
    for (int x = 0; x < test.Length; x++)
    {
        if (test[x] == 'd' || test[x] == 'x' || test[x] == '?')
        {
            result = x;
            break;
        }
    }
    if (result != 3)
    {
        return;
    }
}
s2.Stop();
Console.WriteLine(s1.Elapsed.TotalMilliseconds);
Console.WriteLine(s2.Elapsed.TotalMilliseconds);36.7644 ms    IndexOfAny
 6.175  ms    For-loop

Notes, forward-only

IndexOfAny() always performs a forward-only (left to right) scan of the input string. You can use the LastIndexOfAny method for a reversed scan.

IndexOfAny provides a way to scan an input string declaratively for the first occurrence of any of the characters in the parameter char array. This method reduces loop nesting.

IndexOfAny

Some examples

IndexOfAny benchmark

Notes, forward-only

`IndexOfAny`

`IndexOfAny` benchmark