C# Array.Clear Examples

Use the Array.Clear method to zero out all array elements. Measure the performance of Clear.
Array.Clear. This method zeros out elements in a range. It provides a one-line, reliable and understandable way to empty or clear your array.
This method works on arrays of any type—including numbers, booleans, structs and class instances. We can provide a start index, and a length.Array
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.Char Array

Program: We use Array.Clear to reset all elements in an int array to zero, without reallocating the array or changing its reference.

Int Array

Length: We use the Length property of the array as the third argument. This clears all elements.

Array Length
C# program that uses Array.Clear using System; class Program { static void Main() { int[] integerArray = new int[] { 4, 6, 8, 1, 3 }; // // Display the array // Console.WriteLine("--- Integer array before ---"); foreach (int value in integerArray) { Console.WriteLine(value); } // // Clear all elements in the array. // Array.Clear(integerArray, 0, integerArray.Length); // // Display the array // Console.WriteLine("--- Integer array after ---"); foreach (int value in integerArray) { Console.WriteLine(value); } } } Output --- Integer array before --- 4 6 8 1 3 --- Integer array after --- 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.Null

Here: The first argument to Array.Clear is the target array to clear. And the second specifies the offset to start clearing at.

Tip: The third argument uses Math.Min to clear either 2 elements or all elements, whichever is smaller.

Also: If you clear 2 elements and the array has one element, you will get an error. Math.Min prevents this exception.

Math.Max, Min
C# program that clears object array 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"); } } } } Output --- 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.

Version 1: The Array.Clear method is invoked. It clears the 128-element int array that was allocated as a local variable.

Version 2: Here we use a for-loop and assign each element to zero. We time this version and the previous version.

Result: The for-loop version may be faster because we use 0 directly, instead of a "default" value.

C# program that benchmarks Array.Clear using System; using System.Diagnostics; class Program { const int _max = 10000; static void Main() { 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")); } } Output 280.49 ns Array.Clear 45.23 ns for
A 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.

Note: All struct fields will be set to null or 0, depending on their type. The default value can be found with the default operator.

A 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.
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