.NET中的结构和类有什么区别?


当前回答

结构是实际值-它们可以为空,但不能为空

这是正确的,但是也要注意,从.NET2开始,结构支持Nullable版本,C#提供了一些语法糖,使其更易于使用。

int? value = null;
value  = 1;

其他回答

结构是实际值-它们可以为空,但不能为空

这是正确的,但是也要注意,从.NET2开始,结构支持Nullable版本,C#提供了一些语法糖,使其更易于使用。

int? value = null;
value  = 1;

我♥ 可视化,在这里我创建了一个来展示结构和类之间的基本区别。


以及文本表示,以防万一;)

+--------------------------------------------------+------+----------------------------------------------+
|                      Struct                      |      |                      Class                    |
+--------------------------------------------------+------+----------------------------------------------+
| - 1 per Thread.                                  |      | - 1 per application.                         |
|                                                  |      |                                              |
| - Holds value types.                             |      | - Holds reference types.                     |
|                                                  |      |                                              |
| - Types in the stack are positioned              |      | - No type ordering (data is fragmented).     |
|   using the LIFO principle.                      |      |                                              |
|                                                  |      |                                              |
| - Can't have a default constructor and/or        |      | - Can have a default constructor             |
|   finalizer(destructor).                         |      |   and/or finalizer.                          |
|                                                  |      |                                              |
| - Can be created with or without a new operator. |      | - Can be created only with a new operator.   |
|                                                  |      |                                              |
| - Can't derive from the class or struct          |  VS  | - Can have only one base class and/or        |
|   but can derive from the multiple interfaces.   |      |   derive from multiple interfaces.           |
|                                                  |      |                                              |
| - The data members can't be protected.           |      | - Data members can be protected.             |
|                                                  |      |                                              |
| - Function members can't be                      |      | - Function members can be                    |
|   virtual or abstract.                           |      |   virtual or abstract.                       |
|                                                  |      |                                              |
| - Can't have a null value.                       |      | - Can have a null value.                     |
|                                                  |      |                                              |
| - During an assignment, the contents are         |      | - Assignment is happening                    |
|   copied from one variable to another.           |      |   by reference.                              |
+--------------------------------------------------+------+----------------------------------------------+

有关更多信息,请查看以下内容:

类和结构(官方文档)。在类和结构之间选择(官方文档)。

Struct Class
Type Value-type Reference-type
Where On stack / Inline in containing type On Heap
Deallocation Stack unwinds / containing type gets deallocated Garbage Collected
Arrays Inline, elements are the actual instances of the value type Out of line, elements are just references to instances of the reference type residing on the heap
Al-Del Cost Cheap allocation-deallocation Expensive allocation-deallocation
Memory usage Boxed when cast to a reference type or one of the interfaces they implement,
Unboxed when cast back to value type
(Negative impact because boxes are objects that are allocated on the heap and are garbage-collected)
No boxing-unboxing
Assignments Copy entire data Copy the reference
Change to an instance Does not affect any of its copies Affect all references pointing to the instance
Mutability Should be immutable Mutable
Population In some situations Majority of types in a framework should be classes
Lifetime Short-lived Long-lived
Destructor Cannot have Can have
Inheritance Only from an interface Full support
Polymorphism No Yes
Sealed Yes When have sealed keyword (C#), or Sealed attribute (F#)
Constructor Can not have explicit parameterless constructors Any constructor
Null-assignments When marked with nullable question mark Yes (When marked with nullable question mark in C# 8+ and F# 5+ 1)
Abstract No When have abstract keyword (C#), or AbstractClass attribute (F#)
Member Access Modifiers public, private, internal public, protected, internal, protected internal, private protected

1不鼓励在F#中使用null,请改用Option类型。

类的实例存储在托管堆上。“包含”实例的所有变量都只是对堆上实例的引用。将对象传递给方法会导致传递引用的副本,而不是对象本身。

结构(从技术上讲,值类型)存储在使用它们的任何地方,很像原始类型。运行时可以随时复制内容,而无需调用自定义的复制构造函数。将值类型传递给方法涉及复制整个值,同样无需调用任何自定义代码。

C++/CLI名称使这种区别更加明显:“ref class”是第一个类,“value class”是第二个类。C#使用的关键字“class”和“struct”只是必须学习的东西。

除了其他答案中描述的所有差异外:

结构不能具有显式无参数构造函数,而类可以结构不能有析构函数,而类可以结构不能从其他结构或类继承,而类可以从其他类继承。(结构和类都可以从接口实现。)

如果您正在观看一段视频,解释所有的差异,您可以查看第29部分-C#教程-C#中类和结构之间的差异。