Find the number of string occurrences in another string

In C# 2.0 Microsoft introduces some new methods on the String class, one of them being Contains. The Contains method checks if a string in contained within another string in a case-sensitive way. It is very easy to use and a good addition to the String class. However, often you don’t want a case-sensitive search or you want to know how many times a particular string is contained within another. 

Because the String class doesn’t provide us with such methods, we have to create our own. Here are three methods – two overloaded – that does just that.

using System.Text.RegularExpressions;

 

/// <summary>

/// Checks if a string is contained within another.

/// The search is case-insensitive.

/// </summary>

/// <param name="text">The text to search.</param>

/// <param name="stringToFind">The string to look for.</param>

public static bool Contains(string text, string stringToFind)

{

  return NumberOfOccurrences(text, stringToFind) > 0;

}

 

/// <summary>

/// Searches the text for occurrences of a specific string.

/// The search is case-insensitive.

/// </summary>

/// <param name="text">The text to search.</param>

/// <param name="stringToFind">The string to look for.</param>

public static int NumberOfOccurrences(string text, string stringToFind)

{

  return NumberOfOccurrences(text, stringToFind, RegexOptions.IgnoreCase);

}

 

/// <summary>

/// Searches the text for occurrences of a specific string.

/// </summary>

/// <param name="text">The text to search.</param>

/// <param name="stringToFind">The string to look for.</param>

/// <param name="options">Specify the regex option.</param>

public static int NumberOfOccurrences(string text, string stringToFind, RegexOptions options)

{

  if (text == null || stringToFind == null)

  {

    return 0;

  }

 

  Regex reg = new Regex(stringToFind, options);

  return reg.Matches(text).Count;
}

Example of use

if (Contains("Hello world", "hello"))

{

  DoSomething();

}

 

if (NumberOfOccurrences("Hello world", "o") > 1)

{

  DoSomething();

}

 

if (NumberOfOccurrences("Hello world", "o", RegexOptions.None) = 2)

{

  DoSomething();
}

Let’s hope they add similar functionality to the .NET Framework in the future. To read more on regular expression, read this guide on MSDN.