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List<T>.Capacity Property

Gets or sets the total number of elements the internal data structure can hold without resizing.

Namespace:  System.Collections.Generic
Assembly:  mscorlib (in mscorlib.dll)

public int Capacity { get; set; }

Property Value

Type: System.Int32
The number of elements that the List<T> can contain before resizing is required.

ExceptionCondition
ArgumentOutOfRangeException

Capacity is set to a value that is less than Count.

OutOfMemoryException

There is not enough memory available on the system.

Capacity is the number of elements that the List<T> can store before resizing is required, while Count is the number of elements that are actually in the List<T>.

Capacity is always greater than or equal to Count. If Count exceeds Capacity while adding elements, the capacity is increased by automatically reallocating the internal array before copying the old elements and adding the new elements.

The capacity can be decreased by calling the TrimExcess method or by setting the Capacity property explicitly. When the value of Capacity is set explicitly, the internal array is also reallocated to accommodate the specified capacity, and all the elements are copied.

Retrieving the value of this property is an O(1) operation; setting the property is an O(n) operation, where n is the new capacity.

The following code example shows the Capacity property at several points in the life of a list. The default constructor is used to create a list of strings with a capacity of 0, and the Capacity property is displayed to demonstrate this. After the Add method has been used to add several items, the items are listed, and then the Capacity property is displayed again, along with the Count property, to show that the capacity has been increased as needed.

The Capacity property is displayed again after the TrimExcess method is used to reduce the capacity to match the count. Finally, the Clear method is used to remove all items from the list, and the Capacity and Count properties are displayed again.

using System;
using System.Collections.Generic;

public class Example
{
    public static void Main()
    {
        List<string> dinosaurs = new List<string>();

        Console.WriteLine("\nCapacity: {0}", dinosaurs.Capacity);

        dinosaurs.Add("Tyrannosaurus");
        dinosaurs.Add("Amargasaurus");
        dinosaurs.Add("Mamenchisaurus");
        dinosaurs.Add("Deinonychus");
        dinosaurs.Add("Compsognathus");

        Console.WriteLine();
        foreach(string dinosaur in dinosaurs)
        {
            Console.WriteLine(dinosaur);
        }

        Console.WriteLine("\nCapacity: {0}", dinosaurs.Capacity);
        Console.WriteLine("Count: {0}", dinosaurs.Count);

        Console.WriteLine("\nContains(\"Deinonychus\"): {0}",
            dinosaurs.Contains("Deinonychus"));

        Console.WriteLine("\nInsert(2, \"Compsognathus\")");
        dinosaurs.Insert(2, "Compsognathus");

        Console.WriteLine();
        foreach(string dinosaur in dinosaurs)
        {
            Console.WriteLine(dinosaur);
        }

        Console.WriteLine("\ndinosaurs[3]: {0}", dinosaurs[3]);

        Console.WriteLine("\nRemove(\"Compsognathus\")");
        dinosaurs.Remove("Compsognathus");

        Console.WriteLine();
        foreach(string dinosaur in dinosaurs)
        {
            Console.WriteLine(dinosaur);
        }

        dinosaurs.TrimExcess();
        Console.WriteLine("\nTrimExcess()");
        Console.WriteLine("Capacity: {0}", dinosaurs.Capacity);
        Console.WriteLine("Count: {0}", dinosaurs.Count);

        dinosaurs.Clear();
        Console.WriteLine("\nClear()");
        Console.WriteLine("Capacity: {0}", dinosaurs.Capacity);
        Console.WriteLine("Count: {0}", dinosaurs.Count);
    }
}

/* This code example produces the following output:

Capacity: 0

Tyrannosaurus
Amargasaurus
Mamenchisaurus
Deinonychus
Compsognathus

Capacity: 8
Count: 5

Contains("Deinonychus"): True

Insert(2, "Compsognathus")

Tyrannosaurus
Amargasaurus
Compsognathus
Mamenchisaurus
Deinonychus
Compsognathus

dinosaurs[3]: Mamenchisaurus

Remove("Compsognathus")

Tyrannosaurus
Amargasaurus
Mamenchisaurus
Deinonychus
Compsognathus

TrimExcess()
Capacity: 5
Count: 5

Clear()
Capacity: 5
Count: 0
 */

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0

.NET Compact Framework

Supported in: 3.5, 2.0

XNA Framework

Supported in: 3.0, 2.0, 1.0

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