C# | Check if an array is read-only or not

Last Updated : 01 Feb, 2019

Array.IsReadOnly Property is used to get a value that indicates whether the Array is read-only or not.

Syntax:

public bool IsReadOnly { get; }

Property Value: This property always returns false for all arrays.

Below programs illustrate the use of above-discussed property:

Example 1:

// C# program to illustrate 
// IsReadOnly Property of 
// Array class 
using System; 
namespace geeksforgeeks { 
  
class GFG { 
  
    // Main Method 
    public static void Main() 
    { 
  
        // declares an 1D Array of string 
        string[] topic; 
  
        // assigning null to array 
        topic = new string[] { null }; 
  
        // Here we check whether is 
        // array of fixed size or not 
        Console.WriteLine("Result: " + topic.IsReadOnly); 
    } 
} 
} 

Output:

Result: False

Example 2:

// C# program to illustrate 
// IsReadOnly Property of 
// Array class 
using System; 
namespace geeksforgeeks { 
  
class GFG { 
  
    // Main Method 
    public static void Main() 
    { 
  
        // Two-dimensional array  
        int[, ] arr = new int[, ] {{1, 2},  
                                   {3, 4},   
                                   {5, 6},   
                                   {7, 8}};  
  
  
        // Here we check whether is 
        // array of fixed size or not 
        Console.WriteLine("Result: " + arr.IsReadOnly); 
    } 
} 
} 

Output:

Result: False

Note:

Array implements the IsReadOnly property because it is needed by the System.Collections.IList interface.
An array which is read-only does not allow the addition, removal, or modification of elements after the creation of an array.
If a user requires a read-only collection, then he or she must use a System.Collections class which implements the System.Collections.IList interface.
If a user cast or convert an array to an IList interface object, the IList.IsReadOnly property returns false. However, if the user cast or convert an array to an IList<T> interface, the IsReadOnly property returns true.
Retrieving the value of this property is an O(1) operation.

Reference:

https://docs.microsoft.com/en-us/dotnet/api/system.array.isreadonly?view=netframework-4.7.2

C# | Check if a SortedList is read-only

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