类型转换在C＃ [英] Typecasting in C#

问题描述

什么是类型转换，有什么用的呢？它是如何工作的？请提供样品教程..我没有得到从谷歌好。

What is type casting, whats the use of this? How it work? please provide the sample tutorial .. i didnt get good one from google.

推荐答案

铸造通常是告诉，虽然它只是知道一个值是一些通用型的编译器的问题，你知道它的实际一个更具体的类型。例如：

Casting is usually a matter of telling the compiler that although it only knows that a value is of some general type, you know it's actually of a more specific type. For example:

object x = "hello";

...

// I know that x really refers to a string
string y = (string) x;

有各种转换运营商。在（类型名）前pression 的形式可以做三不同的事情：

There are various conversion operators. The (typename) expression form can do three different things:

• 取消装箱转换（例如，从盒装整数 INT ）


• 一个用户定义的转换（例如铸造 XAttribute 到字符串）


• 一个类型层次结构中的引用转换（例如铸造对象到字符串）

• An unboxing conversion (e.g. from a boxed integer to int)
• A user-defined conversion (e.g. casting XAttribute to string)
• A reference conversion within a type hierarchy (e.g. casting object to string)

所有这些可能无法执行时，在这种情况下会抛出异常。

All of these may fail at execution time, in which case an exception will be thrown.

的为运营商，而另一方面，从不抛出异常 - 相反，转换的结果是空如果失败：

The as operator, on the other hand, never throws an exception - instead, the result of the conversion is null if it fails:

object x = new object();
string y = x as string; // Now y is null because x isn't a string

它可用于拆箱到一个空值类型：

It can be used for unboxing to a nullable value type:

object x = 10; // Boxed int
float? y = x as float?; // Now y has a null value because x isn't a boxed float

也有隐式转换，例如从 INT 到长：

int x = 10;
long y = x; // Implicit conversion

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