C＃位或需要使用字节铸造* *有时 [英] C# Bitwise OR needs casting with byte *sometimes*

问题描述

我发现在C＃编译器一个奇怪的局面。为什么下面的演员是必填的

 使用系统; 
 
类节目
 {
私人常量字节BIT_ZERO_SET = 1; 
私人常量字节BIT_ONE_SET = 2; 
私人常量字节BIT_TWO_SET = 4; 
 
静态无效的主要（字串[] args）
 {
字节B = BIT_ZERO_SET | BIT_ONE_SET; 
 Console.WriteLine（二）; 
 
 //不能编译，需要说投为int。 
 // B = | BIT_TWO_SET; 
 
 //Compiles...ugly 
 B =（字节）（B | BIT_TWO_SET）; 
 Console.WriteLine（二）; 
 
 Console.WriteLine（按回车键。）; 
到Console.ReadLine（）; 
} 
} 
  

感谢。

< DIV CLASS =h2_lin>解决方案

的嫌疑，该行：

 字节b = BIT_ZERO_SET | BIT_ONE_SET; 
  

实际上是由C＃编译器处理成恒定值的分配给b，而不是逐位。操作 - 它可以这样做，因为表达式的右边是在编译时完全确定。

行：

  // b = | BIT_TWO_SET; 
  

不编译因为逐位或运算促进其元素和评估为int，不一个字节。因为它涉及到运行值（B），它不能被编译成一个恒定的分配一样前行，需要铸造。

I found an odd situation in the C# compiler. Why the cast below is required?

using System;

class Program
{
    private const byte BIT_ZERO_SET = 1;
    private const byte BIT_ONE_SET = 2;
    private const byte BIT_TWO_SET = 4;

    static void Main(string[] args)
    {
        byte b = BIT_ZERO_SET | BIT_ONE_SET;
        Console.WriteLine(b);

        //Does not compile, says needs to cast to int.
        //b = b | BIT_TWO_SET;

        //Compiles...ugly
        b = (byte)(b | BIT_TWO_SET);
        Console.WriteLine(b);

        Console.WriteLine("Press enter.");
        Console.ReadLine();    
    }
}

Thanks.

解决方案

Is suspect that the line:

byte b = BIT_ZERO_SET | BIT_ONE_SET;

is actually processed by the C# compiler into an assignment of a constant value to b, rather than a bitwise operation - it can do this because the right side of the expression is fully defined at compile time.

The line:

//b = b | BIT_TWO_SET;

doesn't compiled because the bit-wise OR operator promotes its elements and evaluates to an int, not a byte. Since it involves a runtime value (b) it cannot be compiled into a constant assignment like the line before, and requires casting.

这篇关于C＃位或需要使用字节铸造* *有时的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！