Structure containing bit mask

I'm parsing a byte[] to a structure using StructLayout. I've managed to get this to work for integers, arrays, etc but I need to check for bits too. So something like this in C++.

Code:

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      struct
      {
        unsigned short  one    : 6;
        unsigned short  two    : 5;
        unsigned short  three  : 5;     
      } field;

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I guess I need to use BitArray but I've been unbale to get this to work with StructLayout.

Could anyone point me in the correct direction?
Thank you.

There is not concept of Bit mask in C# as there is in C++; Let someone correct me if I am wrong.

Are you going to handle data between managed and unmanaged code so you need to use StructLayout ? Whats the exact problem you want to get handled with this?

Basically if you need to use a bitmask you can do it in the properties
of the struct

Code:

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private int data;
public byte MyFirstBit{
        get {return this.data & 0x00000001;}
        set { // kill existing bit in this place
                        this.data &= 0x11111110;
                        // set new bit
                        this.data |= value & 0x00000001;
        }
}

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Depending on your needs you also can use an indexer checking each bit you need using the index running from bit ti bit.

I'm simply reading a byte[] from a file. This file has a pre-defined layout. So for example..

uint32 value1 (bytes 0 -3)
uint16 value2 (4-5)
byte value 3 (6)

I can get these values fine but value2 could then be broken down further.

value2 -> 1st 12bits are a numeric field and the remaining bits are single byte flags.

As you say I could use setter to parse the value correctly but I wanted to make sure it wasn't possible to do someting like:

uint32 value1
BitArray value 2_1[12]
BitArray value 2_2[1]
BitArray value 2_3[1]
BitArray value 2_4[1]
BitArray value 2_5[1]
byte value3

I hope this explains exactly what I hope to do. Maybe it's not possible and byte is the smallest "unit" for StructLayout.

Thanks.

Code:

---

using System;
using System.Runtime.InteropServices;

static class Program {
    static void Main() {
        byte[] bytes = { 0x02, 0x16, 0xaf, 0xff, 0xaa, 0x00, 0x01 };
        GCHandle bHand = GCHandle.Alloc(bytes, GCHandleType.Pinned);
        Field f = (Field)Marshal.PtrToStructure(bHand.AddrOfPinnedObject(), typeof(Field));
        bHand.Free();
        // Here f will contain the values from the byte array
    }
}

[StructLayout(LayoutKind.Explicit, Pack = 1)]
public struct Field {
    [FieldOffset(0)]
    public uint one;
    [FieldOffset(sizeof(uint))]
    public ushort two;
    [FieldOffset(sizeof(uint) + sizeof(ushort))]
    public byte three;
}

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Quote:

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Originally Posted by sb101

...
I hope this explains exactly what I hope to do. Maybe it's not possible and byte is the smallest "unit" for StructLayout.

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IMHO Byte is the smallest unit, and bits are handled by using bitmasks as I showed in my example.