C# Cookbook

2.5. Finding the Location of All Occurrencesof a String Within Another String

Problem

You need to search a string for every occurrence of a specific string. In addition, the case-sensitivity, or insensitivity, of the search needs to be controlled.

Solution

Using IndexOf or IndexOfAny in a loop, we can determine how many occurrences of a character or string exist as well as their locations within the string. To find each occurrence of a case-sensitive string in another string, use the following code:

using System;
using System.Collections;

public static int[] FindAll(string matchStr, string searchedStr, int startPos)
{
    int foundPos = -1;   // -1 represents not found
    int count = 0;
    ArrayList foundItems = new ArrayList( );

    do
    {
       foundPos = searchedStr.IndexOf(matchStr, startPos);
       if (foundPos > -1)
       {
          startPos = foundPos + 1;
          count++;
          foundItems.Add(foundPos);

          Console.WriteLine("Found item at position: " + foundPos.ToString( ));
       }
    }while (foundPos > -1 && startPos < searchedStr.Length);

    return ((int[])foundItems.ToArray(typeof(int)));
}

If the FindAll method is called with the following parameters:

int[] allOccurrences = FindAll("Red", "BlueTealRedredGreenRedYellow", 0);

the string "Red" is found at locations 8 and 19 in the string searchedStr. This code uses the IndexOf method inside a loop to iterate through each found matchStr string in the searchStr string.

To find a case-sensitive character in a string, use the following code:

public static int[] FindAll(char MatchChar, string searchedStr, ...