C# | Char.IsLowSurrogate(String, Int32) Method

This method is used to indicates whether the Char object at the specified position in a string is a low surrogate or not. Syntax:

public static bool IsLowSurrogate (string s, int index);

Parameters:

s: It is a String. index: It is the character position to evaluate in s.

Return Value: This method returns true if the numeric value of the specified character in the s parameter ranges from U+DC00 through U+DFFF otherwise it returns false. Exceptions:

• ArgumentNullException: If the s is null.
• ArgumentOutOfRangeException: If the index is not a position within s.

Below programs illustrate the use of Char.IsLowSurrogate(String, Int32) Method: Example 1:

csharp

// C# program to demonstrate
// Char.IsLowSurrogate(String,
// Int32) Method
using System;

class GFG {

    // Main Method
    public static void Main()
    {
        try {

            // calling check() Method
            check("1234", 3);
            check("Tsunami", 3);
            check("psyc0lo", 4);

            // declaring and initializing string s1
            string s1 = new String(new char[] {'a',
                        '\uD800', '\uDC00', 'z' });
            check(s1, 2);
        }
        catch (ArgumentNullException e) {

            Console.Write("Exception Thrown: ");
            Console.Write("{0}", e.GetType(), e.Message);
        }
        catch (ArgumentOutOfRangeException e) {

            Console.Write("Exception Thrown: ");
            Console.Write("{0}", e.GetType(), e.Message);
        }
    }

    // Defining check() method
    public static void check(string s, int i)
    {
        // checking condition
        // using IsLowSurrogate() Method
        bool val = Char.IsLowSurrogate(s, i);

        // checking
        if (val)
            Console.WriteLine("String '{0}' contains Low "
                + "Surrogate value at index {1} ",  s, i);

        else
            Console.WriteLine("String '{0}' doesn't contain any Low"
                           + "Surrogate value at index {1}", s, i);

    }
}

Output:

String '1234' does't contain any LowSurrogate value at index 3
String 'Tsunami' does't contain any LowSurrogate value at index 3
String 'psyc0lo' does't contain any LowSurrogate value at index 4
String 'að??z' contains Low Surrogate value at index 2

Example 2: For ArgumentNullException

csharp

// C# program to demonstrate
// Char.IsLowSurrogate(String,
// Int32) Method
using System;

class GFG {

    // Main Method
    public static void Main()
    {
        try {

            // calling check() Method
            check("1234", 3);
            check("Tsunami", 3);
            check("psyc0lo", 4);

            // declaring and initializing string s1
            string s1 = new String(new char[] {'a',
                        '\uD800', '\uDC00', 'z' });
            check(s1, 2);

            Console.WriteLine("");
            Console.WriteLine("s is null");
            check(null, 4);
        }
        catch (ArgumentNullException e) {

            Console.Write("Exception Thrown: ");
            Console.Write("{0}", e.GetType(), e.Message);
        }
        catch (ArgumentOutOfRangeException e) {

            Console.Write("Exception Thrown: ");
            Console.Write("{0}", e.GetType(), e.Message);
        }
    }

    // Defining check() method
    public static void check(string s, int i)
    {
        // checking condition
        // using IsLowSurrogate() Method
        bool val = Char.IsLowSurrogate(s, i);

        // checking
        if (val)
            Console.WriteLine("String '{0}' contains Low "
                  + "Surrogate value at index {1} ",s, i);

        else
            Console.WriteLine("String '{0}' doesn't contain any Low"
                            + "Surrogate value at index {1}",s, i);

    }
}

Output:

String '1234' does't contain any LowSurrogate value at index 3
String 'Tsunami' does't contain any LowSurrogate value at index 3
String 'psyc0lo' does't contain any LowSurrogate value at index 4
String 'að??z' contains Low Surrogate value at index 2 

s is null
Exception Thrown: System.ArgumentNullException

Example 3: For ArgumentOutOfRangeException

csharp

// C# program to demonstrate
// Char.IsLowSurrogate(String,
// Int32) Method
using System;

class GFG {

    // Main Method
    public static void Main()
    {
        try {

            // calling check() Method
            check("1234", 3);
            check("Tsunami", 3);
            check("psyc0lo", 4);

            // declaring and initializing string s1
            string s1 = new String(new char[] {'a',
                        '\uD800', '\uDC00', 'z' });
            check(s1, 2);

            Console.WriteLine("");
            Console.WriteLine("index is less than zero");
            check("null", -4);
        }
        catch (ArgumentNullException e) {

            Console.Write("Exception Thrown: ");
            Console.Write("{0}", e.GetType(), e.Message);
        }
        catch (ArgumentOutOfRangeException e) {

            Console.Write("Exception Thrown: ");
            Console.Write("{0}", e.GetType(), e.Message);
        }
    }

    // Defining check() method
    public static void check(string s, int i)
    {
        // checking condition
        // using IsLowSurrogate() Method
        bool val = Char.IsLowSurrogate(s, i);

        // checking
        if (val)
            Console.WriteLine("String '{0}' contains Low "
                  + "Surrogate value at index {1} ",s, i);

        else
            Console.WriteLine("String '{0}' doesn't contain any Low"
                            + "Surrogate value at index {1}",s, i);

    }
}

Output:

String '1234' does't contain any LowSurrogate value at index 3
String 'Tsunami' does't contain any LowSurrogate value at index 3
String 'psyc0lo' does't contain any LowSurrogate value at index 4
String 'að??z' contains Low Surrogate value at index 2 

index is less than zero
Exception Thrown: System.ArgumentOutOfRangeException

Reference:

• https://docs.microsoft.com/en-us/dotnet/api/system.char.islowsurrogate?view=netframework-4.7.2#System_Char_IsLowSurrogate_System_String_System_Int32_