Stack<T> Constructor

Initializes a new instance of the Stack<T> class that is empty and has the default initial capacity.

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

public Stack()

The capacity of a Stack<T> is the number of elements that the Stack<T> can hold. As elements are added to a Stack<T>, the capacity is automatically increased as required by reallocating the internal array.

If the size of the collection can be estimated, specifying the initial capacity eliminates the need to perform a number of resizing operations while adding elements to the Stack<T>.

The capacity can be decreased by calling TrimExcess.

This constructor is an O(1) operation.

The following code example demonstrates this constructor and several methods of the Stack<T> generic class.

The code example creates a stack of strings with default capacity and uses the Push method to push five strings onto the stack. The elements of the stack are enumerated, which does not change the state of the stack. The Pop method is used to pop the first string off the stack. The Peek method is used to look at the next item on the stack, and then the Pop method is used to pop it off.

The ToArray method is used to create an array and copy the stack elements to it, then the array is passed to the Stack<T> constructor that takes IEnumerable<T>, creating a copy of the stack with the order of the elements reversed. The elements of the copy are displayed.

An array twice the size of the stack is created, and the CopyTo method is used to copy the array elements beginning at the middle of the array. The Stack<T> constructor is used again to create a copy of the stack with the order of elements reversed; thus, the three null elements are at the end.

The Contains method is used to show that the string "four" is in the first copy of the stack, after which the Clear method clears the copy and the Count property shows that the stack is empty.

using System;
using System.Collections.Generic;

class Example
    public static void Main()
        Stack<string> numbers = new Stack<string>();

        // A stack can be enumerated without disturbing its contents. 
        foreach( string number in numbers )

        Console.WriteLine("\nPopping '{0}'", numbers.Pop());
        Console.WriteLine("Peek at next item to destack: {0}", 
        Console.WriteLine("Popping '{0}'", numbers.Pop());

        // Create a copy of the stack, using the ToArray method and the 
        // constructor that accepts an IEnumerable<T>.
        Stack<string> stack2 = new Stack<string>(numbers.ToArray());

        Console.WriteLine("\nContents of the first copy:");
        foreach( string number in stack2 )

        // Create an array twice the size of the stack and copy the 
        // elements of the stack, starting at the middle of the  
        // array.  
        string[] array2 = new string[numbers.Count * 2];
        numbers.CopyTo(array2, numbers.Count);

        // Create a second stack, using the constructor that accepts an 
        // IEnumerable(Of T).
        Stack<string> stack3 = new Stack<string>(array2);

        Console.WriteLine("\nContents of the second copy, with duplicates and nulls:");
        foreach( string number in stack3 )

        Console.WriteLine("\nstack2.Contains(\"four\") = {0}", 

        Console.WriteLine("\nstack2.Count = {0}", stack2.Count);

/* This code example produces the following output:


Popping 'five'
Peek at next item to destack: four
Popping 'four'

Contents of the first copy:

Contents of the second copy, with duplicates and nulls:

stack2.Contains("four") = False


stack2.Count = 0

.NET Framework


.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps




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