Stack<T>.GetEnumerator 方法

参考

定义

命名空间:: System.Collections.Generic

程序集:: System.Collections.dll

程序集:: System.dll

程序集:: netstandard.dll

Source:: Stack.cs

Source:: Stack.cs

Source:: Stack.cs

重要

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返回 Stack<T> 的一个枚举数。

public:
 System::Collections::Generic::Stack<T>::Enumerator GetEnumerator();

public System.Collections.Generic.Stack<T>.Enumerator GetEnumerator ();

member this.GetEnumerator : unit -> System.Collections.Generic.Stack<'T>.Enumerator

Public Function GetEnumerator () As Stack(Of T).Enumerator

Stack<T>.Enumerator

Stack<T>.Enumerator 的一个 Stack<T>。

示例

下面的代码示例演示 Stack<T> 泛型类是可枚举的。 foreach在 Visual Basic 中 (For Each Cfor each++) 语句用于枚举堆栈。

该代码示例创建一个具有默认容量的字符串堆栈， Push 并使用方法将五个字符串推送到堆栈上。堆栈的元素是枚举的，这不会更改堆栈的状态。方法 Pop 用于从堆栈中弹出第一个字符串。方法 Peek 用于查看堆栈上的下一项，然后使用 Pop 方法将其弹出。

方法 ToArray 用于创建数组并将堆栈元素复制到其中，然后将数组传递给 Stack<T> 采用 IEnumerable<T>的构造函数，创建堆栈的副本，并按元素的顺序反转。将显示副本的元素。

创建一个两倍于堆栈大小的数组，并使用 CopyTo 方法复制从数组中间开始的数组元素。构造 Stack<T> 函数再次用于创建堆栈的副本，其元素顺序为反转;因此，三个 null 元素位于末尾。

方法 Contains 用于显示字符串“four”位于堆栈的第一个副本中，然后 Clear 方法清除副本，属性 Count 显示堆栈为空。

using System;
using System.Collections.Generic;

class Example
{
    public static void Main()
    {
        Stack<string> numbers = new Stack<string>();
        numbers.Push("one");
        numbers.Push("two");
        numbers.Push("three");
        numbers.Push("four");
        numbers.Push("five");

        // A stack can be enumerated without disturbing its contents.
        foreach( string number in numbers )
        {
            Console.WriteLine(number);
        }

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

        // 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(number);
        }

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

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

/* This code example produces the following output:

five
four
three
two
one

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

Contents of the first copy:
one
two
three

Contents of the second copy, with duplicates and nulls:
one
two
three




stack2.Contains("four") = False

stack2.Clear()

stack2.Count = 0
 */

open System
open System.Collections.Generic

let numbers = Stack()
numbers.Push "one"
numbers.Push "two"
numbers.Push "three"
numbers.Push "four"
numbers.Push "five"

// A stack can be enumerated without disturbing its contents.
for number in numbers do
    printfn $"{number}"

printfn $"\nPopping '{numbers.Pop()}'"
printfn $"Peek at next item to destack: {numbers.Peek()}"
numbers.Peek() |> ignore
printfn $"Popping '{numbers.Pop()}'"

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

printfn "\nContents of the first copy:"

for number in stack2 do
    printfn $"{number}"

// Create an array twice the size of the stack and copy the
// elements of the stack, starting at the middle of the
// array.
let array2 = numbers.Count * 2 |> Array.zeroCreate
numbers.CopyTo(array2, numbers.Count)

// Create a second stack, using the constructor that accepts an
// IEnumerable(Of T).
let stack3 = Stack array2

printfn "\nContents of the second copy, with duplicates and nulls:"

for number in stack3 do
    printfn $"{number}"

printfn
    $"""
stack2.Contains "four" = {stack2.Contains "four"}"""

printfn "\nstack2.Clear()"
stack2.Clear()
printfn $"\nstack2.Count = {stack2.Count}"

// This code example produces the following output:
//       five
//       four
//       three
//       two
//       one
//
//       Popping 'five'
//       Peek at next item to destack: four
//       Popping 'four'
//
//       Contents of the first copy:
//       one
//       two
//       three
//
//       Contents of the second copy, with duplicates and nulls:
//       one
//       two
//       three
//
//       stack2.Contains("four") = False
//
//       stack2.Clear()
//
//       stack2.Count = 0

Imports System.Collections.Generic

Module Example

    Sub Main

        Dim numbers As New Stack(Of String)
        numbers.Push("one")
        numbers.Push("two")
        numbers.Push("three")
        numbers.Push("four")
        numbers.Push("five")

        ' A stack can be enumerated without disturbing its contents.
        For Each number As String In numbers
            Console.WriteLine(number)
        Next

        Console.WriteLine(vbLf & "Popping '{0}'", numbers.Pop())
        Console.WriteLine("Peek at next item to pop: {0}", _
            numbers.Peek())    
        Console.WriteLine("Popping '{0}'", numbers.Pop())

        ' Create another stack, using the ToArray method and the
        ' constructor that accepts an IEnumerable(Of T). Note that
        ' the order of items on the new stack is reversed.
        Dim stack2 As New Stack(Of String)(numbers.ToArray())

        Console.WriteLine(vbLf & "Contents of the first copy:")
        For Each number As String In stack2
            Console.WriteLine(number)
        Next
        
        ' Create an array twice the size of the stack, compensating
        ' for the fact that Visual Basic allocates an extra array 
        ' element. Copy the elements of the stack, starting at the
        ' middle of the array. 
        Dim array2((numbers.Count * 2) - 1) As String
        numbers.CopyTo(array2, numbers.Count)
        
        ' Create a second stack, using the constructor that accepts an
        ' IEnumerable(Of T). The elements are reversed, with the null
        ' elements appearing at the end of the stack when enumerated.
        Dim stack3 As New Stack(Of String)(array2)

        Console.WriteLine(vbLf & _
            "Contents of the second copy, with duplicates and nulls:")
        For Each number As String In stack3
            Console.WriteLine(number)
        Next

        Console.WriteLine(vbLf & "stack2.Contains(""four"") = {0}", _
            stack2.Contains("four"))

        Console.WriteLine(vbLf & "stack2.Clear()")
        stack2.Clear()
        Console.WriteLine(vbLf & "stack2.Count = {0}", _
            stack2.Count)
    End Sub
End Module

' This code example produces the following output:
'
'five
'four
'three
'two
'one
'
'Popping 'five'
'Peek at next item to pop: four
'Popping 'four'
'
'Contents of the first copy:
'one
'two
'three
'
'Contents of the second copy, with duplicates and nulls:
'one
'two
'three
'
'
'
'
'stack2.Contains("four") = False
'
'stack2.Clear()
'
'stack2.Count = 0

注解

foreach Visual Basic) for each C++ For Each 中 C# 语言 (语句隐藏枚举器的复杂性。因此，建议使用 foreach，而不是直接操作枚举数。

枚举器可用于读取集合中的数据，但不能用于修改基础集合。

最初，枚举数定位在集合中第一个元素的前面。在此位置上，未定义 Current。因此，在读取 MoveNext 的值之前，必须调用 Current 将枚举器向前移动到集合的第一个元素。

在调用 Current 之前，MoveNext 返回相同的对象。 MoveNext 将 Current 设置为下一个元素。

如果 MoveNext 传递集合的末尾，则枚举器位于集合中的最后一个元素之后，并 MoveNext 返回 false。当枚举器位于此位置时，对 MoveNext 的后续调用也会返回 false。如果最后一次MoveNext调用返回，falseCurrent则为未定义。无法再次将 Current 设置为集合的第一个元素；必须改为创建新的枚举器实例。

只要集合保持不变，枚举器就仍有效。如果对集合进行了更改（例如添加、修改或删除元素），枚举器将不可恢复地失效，下一次InvalidOperationException调用 MoveNext 或 IEnumerator.Reset 引发。

枚举数没有对集合的独占访问权；因此，从头到尾对一个集合进行枚举在本质上不是一个线程安全的过程。若要确保枚举过程中的线程安全性，可以在整个枚举过程中锁定集合。若要允许多个线程访问集合以进行读写操作，则必须实现自己的同步。

中 System.Collections.Generic 集合的默认实现不同步。

此方法是 O (1) 操作。

适用于

Stack<T>.GetEnumerator 方法

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注解

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