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

In C#, all arrays have a fixed size once they are created. You cannot change the length of an array after initialization. To check if an array has a fixed size, use the IsFixedSize property, which always returns true for arrays.

Syntax

Following is the syntax to check if an array has fixed size −

bool isFixed = arrayName.IsFixedSize;

Using IsFixedSize Property

Example

using System;

public class Demo {
    public static void Main() {
        string[] products = new string[] { "Electronics", "Accessories", "Clothing", "Toys", "Furniture" };
        
        Console.WriteLine("Products list...");
        foreach(string s in products) {
            Console.WriteLine(s);
        }
        
        Console.WriteLine("Array Length: " + products.Length);
        Console.WriteLine("Is the array having fixed size? = " + products.IsFixedSize);
        Console.WriteLine("Is the array read-only? = " + products.IsReadOnly);
    }
}

The output of the above code is −

Products list...
Electronics
Accessories
Clothing
Toys
Furniture
Array Length: 5
Is the array having fixed size? = True
Is the array read-only? = False

Checking Empty Array Size

Example

using System;

public class Demo {
    public static void Main() {
        string[] emptyArray = new string[] { };
        int[] numbers = new int[10];
        
        Console.WriteLine("Empty array length: " + emptyArray.Length);
        Console.WriteLine("Empty array has fixed size? = " + emptyArray.IsFixedSize);
        
        Console.WriteLine("Numbers array length: " + numbers.Length);
        Console.WriteLine("Numbers array has fixed size? = " + numbers.IsFixedSize);
    }
}

The output of the above code is −

Empty array length: 0
Empty array has fixed size? = True
Numbers array length: 10
Numbers array has fixed size? = True

Array vs Dynamic Collections

Unlike dynamic collections such as List<T>, arrays cannot grow or shrink after creation −

Example

using System;
using System.Collections.Generic;

public class Demo {
    public static void Main() {
        // Array - Fixed size
        int[] fixedArray = new int[3] { 1, 2, 3 };
        
        // List - Dynamic size
        List<int> dynamicList = new List<int> { 1, 2, 3 };
        
        Console.WriteLine("Array IsFixedSize: " + fixedArray.IsFixedSize);
        Console.WriteLine("Array Length: " + fixedArray.Length);
        
        Console.WriteLine("List Count before adding: " + dynamicList.Count);
        dynamicList.Add(4);
        Console.WriteLine("List Count after adding: " + dynamicList.Count);
    }
}

The output of the above code is −

Array IsFixedSize: True
Array Length: 3
List Count before adding: 3
List Count after adding: 4

Key Properties of Arrays

Conclusion

In C#, all arrays have a fixed size determined at creation time. The IsFixedSize property always returns true for arrays, indicating that you cannot add or remove elements after initialization. If you need a dynamically resizable collection, consider using List<T> or other collection classes instead.