c# - How to check if StringBuilder contains a substring

Check StringBuilder contains a specified substring
The StringBuilder class represents a mutable String of characters. The StringBuilder class cannot be inherited. The StringBuilder class represents a String-like object whose value is a mutable sequence of characters.

The default capacity of a StringBuilder object is 16 characters and its default maximum capacity is Int32.MaxValue. Although StringBuilder and String both represent sequences of characters, they are implemented differently. The String is an immutable type. So, each operation that appears to modify a String object actually creates a new String.

The following .net c# tutorial code demonstrates how we can check whether a StringBuilder object contains a specified substring within it. So, in this .net c# tutorial code we will determine whether a StringBuilder instance contains a specified substring or not.

There are no direct methods in the StringBuilder class to check whether a substring contains within a StringBuilder instance. So we have to convert the StringBuilder object to a String object to check whether the specified substring exists within a StringBuilder instance or not.

The StringBuilder ToString() method converts the value of a StringBuilder to a String. The String Contains(string value) method returns a value indicating whether a specified substring occurs within this String instance. The String Contains() method returns a Boolean value. It returns true if the value parameter occurs within this String or if the value is the empty String (“”) otherwise it returns false.

The String Contains(string value) method throws ArgumentNullException if the value is null. So, to check whether a StringBuilder instance contains a specified substring we have to convert the StringBuilder object to a String object. After conversion, we have to call String Contains(String) method to check the substring within it.
stringbuilder-contains.aspx

<%@ Page Language="C#" AutoEventWireup="true"%>
<%@ Import Namespace="System.IO" %>
  
<!DOCTYPE html>
  
<script runat="server"> 
    protected void Button1_Click(object sender, System.EventArgs e)  
    {
        StringBuilder stringb = new StringBuilder();
        stringb.Append("Jacobin Cuckoo.");
        stringb.AppendLine();

        stringb.Append("Brush Cuckoo.");
        stringb.AppendLine();

        stringb.Append("Giant Coua.");
        stringb.AppendLine();

        //this line check stringbuilder contains specific substring.
        Boolean result = stringb.ToString().Contains("Brush Cuckoo");
        
        //this is a simple solution for stringbuilder contains alternative
        Boolean result2 = stringb.ToString().Contains("Guira Cuckoo");

        Label1.Text = stringb.ToString();
        Label1.Text += "<br /><br />stringbuilder contains('Brush Cuckoo'): " + result.ToString();
        Label1.Text += "<br />stringbuilder contains('Guira Cuckoo'): " + result2.ToString();
    }  
</script>  
  
<html xmlns="http://www.w3.org/1999/xhtml">  
<head id="Head1" runat="server">  
    <title>c# example - stringbuilder contains</title>  
</head>  
<body>  
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    <div>  
        <h2 style="color:MidnightBlue; font-style:italic;">  
            c# example - stringbuilder contains
        </h2>  
        <hr width="550" align="left" color="Gainsboro" />  
        <br />  
        <asp:Label   
            ID="Label1"   
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            OnClick="Button1_Click"
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    </form>  
</body>  
</html>
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