Csharp 简明教程

C

C# 中的变量被归类为以下类型 −

The variables in C#, are categorized into the following types −

  1. Value types

  2. Reference types

  3. Pointer types

Value Type

值类型变量可以直接被赋值。它们来自类 * System.ValueType*。

Value type variables can be assigned a value directly. They are derived from the class * System.ValueType*.

值类型直接包含数据。一些示例是 int, char, and float ，它分别存储数字、字母和浮点数。当你声明一个 int 类型时，系统会分配内存来存储该值。

The value types directly contain data. Some examples are int, char, and float, which stores numbers, alphabets, and floating point numbers, respectively. When you declare an int type, the system allocates memory to store the value.

下表列出了 C# 2010 中可用的值类型 −

The following table lists the available value types in C# 2010 −

Type

Represents

Range

Default Value

bool

Boolean value

True or False

False

byte

8-bit unsigned integer

0 to 255

0

char

16-bit Unicode character

U +0000 to U +ffff

'\0'

decimal

128-bit precise decimal values with 28-29 significant digits

(-7.9 x 1028 to 7.9 x 1028) / 100 to 28

0.0M

double

64-bit double-precision floating point type

(/-)5.0 x 10-324 to (/-)1.7 x 10308

0.0D

float

32-bit single-precision floating point type

-3.4 x 1038 to + 3.4 x 1038

0.0F

int

32-bit signed integer type

-2,147,483,648 to 2,147,483,647

0

long

64-bit signed integer type

-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807

0L

sbyte

8-bit signed integer type

-128 to 127

0

short

16-bit signed integer type

-32,768 to 32,767

0

uint

32-bit unsigned integer type

0 to 4,294,967,295

0

ulong

64-bit unsigned integer type

0 to 18,446,744,073,709,551,615

0

ushort

16-bit unsigned integer type

0 to 65,535

0

要获取特定平台上某个类型或变量的确切大小，可以使用 sizeof 方法。表达式 sizeof(type) 会产生对象或类型在字节中的存储大小。以下是一个在任何机器上获取 int 类型大小的示例 −

To get the exact size of a type or a variable on a particular platform, you can use the sizeof method. The expression sizeof(type) yields the storage size of the object or type in bytes. Following is an example to get the size of int type on any machine −

using System;

namespace DataTypeApplication {
   class Program {
      static void Main(string[] args) {
         Console.WriteLine("Size of int: {0}", sizeof(int));
         Console.ReadLine();
      }
   }
}

编译并执行上述代码后，将产生以下结果 −

When the above code is compiled and executed, it produces the following result −

Size of int: 4

Reference Type

引用类型不包含存储在变量中的实际数据，但它们包含对变量的引用。

The reference types do not contain the actual data stored in a variable, but they contain a reference to the variables.

换句话说，它们引用一个内存位置。引用类型可以使用多个变量引用内存位置。如果内存位置中的数据被其中一个变量更改，则另一个变量会自动反映此值更改。 built-in 引用类型的示例包括： object 、 dynamic, 和 string 。

In other words, they refer to a memory location. Using multiple variables, the reference types can refer to a memory location. If the data in the memory location is changed by one of the variables, the other variable automatically reflects this change in value. Example of built-in reference types are: object, dynamic, and string.

Object Type

Object Type 是 C# 公共类型系统 (CTS) 中所有数据类型的终极基类。对象是 System.Object 类的一个别名。对象类型可以被赋值任何其他类型、值类型、引用类型、预定义类型或用户定义类型的值。但是，在赋值之前，它需要类型转换。

The Object Type is the ultimate base class for all data types in C# Common Type System (CTS). Object is an alias for System.Object class. The object types can be assigned values of any other types, value types, reference types, predefined or user-defined types. However, before assigning values, it needs type conversion.

当值类型转换为对象类型时，称为 boxing ，另一方面，当对象类型转换为值类型时，称为 unboxing 。

When a value type is converted to object type, it is called boxing and on the other hand, when an object type is converted to a value type, it is called unboxing.

object obj;
obj = 100; // this is boxing

Dynamic Type

可以在 dynamic 数据类型变量中存储任何类型的值。这些类型变量的类型检查在运行时进行。

You can store any type of value in the dynamic data type variable. Type checking for these types of variables takes place at run-time.

声明 dynamic 类型的语法是 −

Syntax for declaring a dynamic type is −

dynamic <variable_name> = value;

例如，

For example,

dynamic d = 20;

动态类型类似于对象类型，但对象类型变量的类型检查发生在编译时，而动态类型变量的类型检查发生在运行时。

Dynamic types are similar to object types except that type checking for object type variables takes place at compile time, whereas that for the dynamic type variables takes place at run time.

String Type

String Type 允许你将任意字符串值赋予变量。字符串类型是 System.String 类的别名。它源自对象类型。字符串类型的变量的值可以使用两种形式的字符串文字进行赋值：quoted 和 @quoted。

The String Type allows you to assign any string values to a variable. The string type is an alias for the System.String class. It is derived from object type. The value for a string type can be assigned using string literals in two forms: quoted and @quoted.

例如，

For example,

String str = "Tutorials Point";

@quoted 字符串文字如下所示：

A @quoted string literal looks as follows −

@"Tutorials Point";

用户定义的引用类型是：类、接口或委托。我们将在后面的章节中讨论这些类型。

The user-defined reference types are: class, interface, or delegate. We will discuss these types in later chapter.

Pointer Type

指针类型变量存储另一种类型内存地址。C# 中的指针具有与 C 或 C++ 中指针相同的功能。

Pointer type variables store the memory address of another type. Pointers in C# have the same capabilities as the pointers in C or C++.

声明指针类型的语法是：

Syntax for declaring a pointer type is −

type* identifier;

例如，

For example,

char* cptr;
int* iptr;

我们将在“不安全代码”一章中讨论指针类型。

We will discuss pointer types in the chapter 'Unsafe Codes'.