为什么原始数据类型在不包含System名称空间的情况下工作

I read that all primitives fall under the System namespace. If I comment out using System, I would expect there to be a build error in my program. However, it is running successfully. Why is this?

我读到所有原语属于System命名空间。如果我使用System注释掉，我希望我的程序中存在构建错误。但是，它正在成功运行。为什么是这样？

3 个解决方案

#1

It's because int is an alias for System.Int32, and since the "Int32" is already prefixed with its namespace (ie. "fully qualified"), the syntax is legal without having to specify using System; at the top of your code.

这是因为int是System.Int32的别名，并且由于“Int32”已经以其命名空间为前缀（即“完全限定”），因此语法是合法的，无需使用System指定;在代码的顶部。

The MSDN snippet below describes this concept-

下面的MSDN片段描述了这个概念 -

Most C# applications begin with a section of using directives. This section lists the namespaces that the application will be using frequently, and saves the programmer from specifying a fully qualified name every time that a method that is contained within is used. For example, by including the line:

大多数C＃应用程序都以using指令的一部分开头。本节列出了应用程序将经常使用的命名空间，并且每次使用其中包含的方法时，都会使程序员不会指定完全限定的名称。例如，通过包含以下行：
using System;
At the start of a program, the programmer can use the code:

在程序开始时，程序员可以使用以下代码：
Console.WriteLine("Hello, World!");
Instead of:

代替：
System.Console.WriteLine("Hello, World!");

System.Int32 (aka "int") would be the latter. Here is an example of this in code -

System.Int32（又名“int”）将是后者。以下是代码中的示例 -

//using System;

namespace Ns
{
    public class Program
    {
        static void Main(string[] args)
        {
            System.Int32 i = 2;    //OK, since we explicitly specify the System namespace
            int j = 2;             //alias for System.Int32, so this is OK too
            Int32 k = 2;           //Error, because we commented out "using System"
        }
    }
}

Since line 11 is not fully qualified / aliasing a fully qualified type, using System; would need to be uncommented for the error to go away.

由于第11行不是完全限定/别名的完全限定类型，因此使用System;需要取消注释才能使错误消失。

Additional references-

其他参考 -

C#, int or Int32? Should I care?

C＃，int还是Int32？我应该关心吗？
Built-In Types Table (C# Reference) (Lists all the built-in types, and their .NET framework equivalents)

内置类型表（C＃参考）（列出所有内置类型及其.NET框架等价物）

#2

As was mention before int is an alias of System.Int32 type. The alias of primitive types are implicitly known by the C# language. Here is the list:

如前所述，int是System.Int32类型的别名。 C＃语言隐含地知道原始类型的别名。这是清单：

object:  System.Object
string:  System.String
bool:    System.Boolean
byte:    System.Byte
sbyte:   System.SByte
short:   System.Int16
ushort:  System.UInt16
int:     System.Int32
uint:    System.UInt32
long:    System.Int64
ulong:   System.UInt64
float:   System.Single
double:  System.Double
decimal: System.Decimal
char:    System.Char

So, for these aliases, also known as simple types, you don't need to specify any namespace.

因此，对于这些别名（也称为简单类型），您不需要指定任何名称空间。

#3

When you use int, you are basically putting in System.Int32. Since this is the fully qualified type name, you don't actually need using System;

当你使用int时，你基本上放入System.Int32。由于这是完全限定的类型名称，因此您实际上不需要使用System;

Your program would work if you did

如果你这样做，你的计划将会奏效

 System.Int32 num = 0;

even without the using

即使没有使用

#1