Array.Clear

This C# method zeros out elements in a range. It is a one-line, reliable and understandable way to empty or clear your array.

Method notes

Clear() works on arrays of any type—including numbers, booleans, structs and class instances. We can provide a start index, and a length.

First example

Many arrays use integers or other value types such as char. In the C# language, these types of arrays are always initialized to 0.

using System;

int[] integerArray = { 4, 6, 8, 1, 3 };
Console.WriteLine(string.Join(",", integerArray));

// Clear all elements in the array.
Array.Clear(integerArray, 0, integerArray.Length);

Console.WriteLine(string.Join(",", integerArray));
4,6,8,1,3
0,0,0,0,0

Example 2

This example shows an array of objects, each with 2 properties. The Array.Clear method is used to set the first 2 references in the array to null.

using System;

class Program
{
    class Employee
    {
        public string Name { get; set; }
        public int Salary { get; set; }
    }

    static void Main()
    {
        Employee[] employees = new Employee[3];
        employees[0] = new Employee() { Name = "Bob", Salary = 10000 };
        employees[1] = new Employee() { Name = "Susan", Salary = 13000 };
        employees[2] = new Employee() { Name = "John", Salary = 20000 };

        //
        // Display the employee array.
        //
        Console.WriteLine("--- Employee array before ---");
        foreach (Employee employee in employees)
        {
            Console.Write(employee.Name);
            Console.Write(": ");
            Console.WriteLine(employee.Salary);
        }
        //
        // Clear first two elements in employee array.
        //
        Array.Clear(employees, 0, Math.Min(2, employees.Length));

        //
        // Display the employee array.
        //
        Console.WriteLine("--- Employee array after ---");
        foreach (Employee employee in employees)
        {
            if (employee != null)
            {
                Console.Write(employee.Name);
                Console.Write(": ");
                Console.WriteLine(employee.Salary);
            }
            else
            {
                Console.WriteLine("null");
            }
        }
    }
}
--- Employee array before ---
Bob: 10000
Susan: 13000
John: 20000
--- Employee array after ---
null
null
John: 20000

Performance, Array.Clear

Here we test the performance of the Array.Clear method. Logically, Array.Clear could be implemented with a for-loop.

using System;
using System.Diagnostics;

const int _max = 10000;
int[] array = new int[128];

// Version 1: clear with Array.Clear.
var s1 = Stopwatch.StartNew();
for (int i = 0; i < _max; i++)
{
    Array.Clear(array, 0, array.Length);
}
s1.Stop();

// Version 2: clear with for-loop.
var s2 = Stopwatch.StartNew();
for (int i = 0; i < _max; i++)
{
    for (int z = 0; z < array.Length; z++)
    {
        array[z] = 0;
    }
}
s2.Stop();
Console.WriteLine(((double)(s1.Elapsed.TotalMilliseconds * 1000000) / _max).ToString("0.00 ns"));
Console.WriteLine(((double)(s2.Elapsed.TotalMilliseconds * 1000000) / _max).ToString("0.00 ns"));
 14.45 ns    Array.Clear
107.94 ns    for

Discussion

Boolean arrays are cleared by having all their elements assigned to false. Also, struct arrays will be cleared the same way as other arrays of System.ValueType instances.

Summary

Array.Clear is frequently useful in programs. It is a one-line way of resetting your entire array to its default values. It works on arrays of values and references.