C# | Check if an Array has fixed size or not

Last Updated : 11 Jul, 2025

Array.IsFixedSize Property is used to get a get a value indicating whether the Array has a fixed size. This property implements the IList.IsFixedSize Property . Syntax:

public bool IsFixedSize { get; }

Property Value: This property is always return true for all arrays. Below programs illustrate the use of above-discussed property: Example 1:

CSharp

// C# program to illustrate
// IsFixedSize of Array class
using System;
namespace geeksforgeeks {

class GFG {

    // Main Method
    public static void Main()
    {

        // declares an 1D Array of string
        string[] topic;

        // allocating memory for topic.
        topic = new string[] {"Array, ", "String, ",
                               "Stack, ", "Queue, ",
                        "Exception, ", "Operators"};

        // Displaying Elements of the array
        Console.WriteLine("Topic of C#:");

        foreach(string ele in topic)
            Console.WriteLine(ele + " ");

        Console.WriteLine();

        // Here we check whether is
        // array of fixed size or not
        Console.WriteLine("Result: " + topic.IsFixedSize);
    }
}
}

Output:

Topic of C#:
Array,  
String,  
Stack,  
Queue,  
Exception,  
Operators 

Result: True

Example 2:

CSharp

// C# program to illustrate
// IsFixedSize of Array class
using System;
namespace geeksforgeeks {

class GFG {

    // Main Method
    public static void Main()
    {

        // declares a 1D Array of string 
        // and assigning null to it
        string[] str = new string[] {null};

        // Here we check whether is
        // array of fixed size or not
        Console.WriteLine("Result: " + str.IsFixedSize);
    }
}
}

Output:

Result: True

Note:

Array implements the IsFixedSize property because it is required by the System.Collections.IList interface.
An array with a fixed size does not allow the addition or removal of elements after the creation of an array, but modification of existing elements are allowed.
Retrieving the value of this property is an O(1) operation.

Reference: