C＃中的位域
我有一个需要填充和写入磁盘的结构（实际上有几个）。
一个例子是：
byte-6
bit0 - original_or_copy
bit1 - copyright
bit2 - data_alignment_indicator
bit3 - PES_priority
bit4-bit5 - PES_scrambling control.
bit6-bit7 - reserved
在CI中可能会做类似如下的事情：
struct PESHeader {
unsigned reserved:2;
unsigned scrambling_control:2;
unsigned priority:1;
unsigned data_alignment_indicator:1;
unsigned copyright:1;
unsigned original_or_copy:1;
};
有什么办法可以在C＃中做到这一点，使我能够使用struct dereferencing点运算符来访问这些位？
对于几个结构，我可以在一个存取函数中进行位移。
我有大量的结构可以用这种方式处理，所以我正在寻找更容易阅读和更快写入的东西。
我可能会使用属性将某些东西敲在一起，然后使用转换类将适当的属性结构转换为位域基元。 就像是...
using System;
namespace BitfieldTest
{
[global::System.AttributeUsage(AttributeTargets.Field, AllowMultiple = false)]
sealed class BitfieldLengthAttribute : Attribute
{
uint length;
public BitfieldLengthAttribute(uint length)
{
this.length = length;
}
public uint Length { get { return length; } }
}
static class PrimitiveConversion
{
public static long ToLong<T>(T t) where T : struct
{
long r = 0;
int offset = 0;
// For every field suitably attributed with a BitfieldLength
foreach (System.Reflection.FieldInfo f in t.GetType().GetFields())
{
object[] attrs = f.GetCustomAttributes(typeof(BitfieldLengthAttribute), false);
if (attrs.Length == 1)
{
uint fieldLength = ((BitfieldLengthAttribute)attrs[0]).Length;
// Calculate a bitmask of the desired length
long mask = 0;
for (int i = 0; i < fieldLength; i++)
mask |= 1 << i;
r |= ((UInt32)f.GetValue(t) & mask) << offset;
offset += (int)fieldLength;
}
}
return r;
}
}
struct PESHeader
{
[BitfieldLength(2)]
public uint reserved;
[BitfieldLength(2)]
public uint scrambling_control;
[BitfieldLength(1)]
public uint priority;
[BitfieldLength(1)]
public uint data_alignment_indicator;
[BitfieldLength(1)]
public uint copyright;
[BitfieldLength(1)]
public uint original_or_copy;
};
public class MainClass
{
public static void Main(string[] args)
{
PESHeader p = new PESHeader();
p.reserved = 3;
p.scrambling_control = 2;
p.data_alignment_indicator = 1;
long l = PrimitiveConversion.ToLong(p);
for (int i = 63; i >= 0; i--)
{
Console.Write( ((l & (1l << i)) > 0) ? "1" : "0");
}
Console.WriteLine();
return;
}
}
}
其中产生预期的... 000101011。 当然，它需要更多的错误检查和更轻松的打字，但是这个概念（我认为）是健全的，可重复使用的，并且可以让你打出十几个易于维护的结构。
adamw
通过使用枚举你可以做到这一点，但看起来很尴尬。
[Flags]
public enum PESHeaderFlags
{
IsCopy = 1, // implied that if not present, then it is an original
IsCopyrighted = 2,
IsDataAligned = 4,
Priority = 8,
ScramblingControlType1 = 0,
ScramblingControlType2 = 16,
ScramblingControlType3 = 32,
ScramblingControlType4 = 16+32,
ScramblingControlFlags = ScramblingControlType1 | ScramblingControlType2 | ... ype4
etc.
}
你想要StructLayoutAttribute
[StructLayout(LayoutKind.Explicit, Size=1, CharSet=CharSet.Ansi)]
public struct Foo
{ [FieldOffset(0)]public byte original_or_copy;
[FieldOffset(0)]public byte copyright;
[FieldOffset(0)]public byte data_alignment_indicator;
[FieldOffset(0)]public byte PES_priority;
[FieldOffset(0)]public byte PES_scrambling_control;
[FieldOffset(0)]public byte reserved;
}
这是一个真正的联盟，但您可以将其用作位域 - 您只需要意识到每个字段的位应该位于字节中的哪个位置。 效用函数和/或常量与AND可以帮助。
const byte _original_or_copy = 1;
const byte _copyright = 2;
//bool ooo = foo.original_or_copy();
static bool original_or_copy(this Foo foo)
{ return (foo.original_or_copy & _original_or_copy) == original_or_copy;
}
还有LayoutKind.Sequential，它可以让你以C的方式做到这一点。
链接地址: http://www.djcxy.com/p/54451.html上一篇: Bit fields in C#