Marshal Not Copying all Data to Fixed Byte Array

**Jeroen Mostert** · Jul 11 '08, 08:45 PM

Re: Marshal Not Copying all Data to Fixed Byte Array

O.B. wrote:

When using Marshal to copy data from a byte array to the structure
below, only the first byte of the "other" array is getting copied from
the original byte array. What do I need to specify to get
Marshal.PtrToSt ructure to copy the all the data into the "other"
array?
>
>
[StructLayout(La youtKind.Explic it, Size = 40)]
unsafe public struct DeadReckoning
{
[FieldOffset(0)]
public byte algorithm; // 1 byte
>
[FieldOffset(1)]
public fixed byte other[15]; // 15 bytes
>
[FieldOffset(16)]
public Vector linearAccelerat ion; // 12 bytes
>
[FieldOffset(28)]
public Vector angularVelocity ; // 12 bytes
}
}
>

What's "Vector"? A structure of 12 bytes?

// Given rawData as a byte array
DeadReckoning dr = new DeadReckoning() ;
IntPtr pData = Marshal.AllocHG lobal(40);
Marshal.Copy(ra wData, 28, pData, 40);

Because you're using an unsafe struct with explicit layout, there's actually
no need to use copying and marshalling at all. You can just write

DeadReckoning dr;
unsafe {
fixed (byte* pData = &rawData[28]) {
dr = *((DeadReckonin g*) pData);
}
}

With this approach, however, you have to verify that "rawData" holds enough
bytes to populate the structure, or it'll copy garbage from the stack. If
you're lucky.

Marshal.PtrToSt ructure(pData, dr);

This shouldn't work, or at least, it doesn't for me. It throws
ArgumentExcepti on because "dr" is a structure. This overload is for classes;
for structures, the right syntax would be

DeadReckoning dr = (DeadReckoning) Marshal.PtrToSt ructure(pData,
typeof(DeadReck oning));

--
J.

**O.B.** · Jul 11 '08, 09:05 PM

Re: Marshal Not Copying all Data to Fixed Byte Array

On Jul 11, 3:40 pm, Jeroen Mostert <jmost...@xs4al l.nlwrote:

O.B. wrote:

When using Marshal to copy data from a byte array to the structure
below, only the first byte of the "other" array is getting copied from
the original byte array. What do I need to specify to get
Marshal.PtrToSt ructure to copy the all the data into the "other"
array?

>

[StructLayout(La youtKind.Explic it, Size = 40)]
unsafe public struct DeadReckoning
{
[FieldOffset(0)]
public byte algorithm; // 1 byte

>

[FieldOffset(1)]
public fixed byte other[15]; // 15 bytes

>

[FieldOffset(16)]
public Vector linearAccelerat ion; // 12 bytes

>

[FieldOffset(28)]
public Vector angularVelocity ; // 12 bytes
}
}

>
What's "Vector"? A structure of 12 bytes?
>

// Given rawData as a byte array
DeadReckoning dr = new DeadReckoning() ;
IntPtr pData = Marshal.AllocHG lobal(40);
Marshal.Copy(ra wData, 28, pData, 40);

>
Because you're using an unsafe struct with explicit layout, there's actually
no need to use copying and marshalling at all. You can just write
>
DeadReckoning dr;
unsafe {
fixed (byte* pData = &rawData[28]) {
dr = *((DeadReckonin g*) pData);
}
}
>
With this approach, however, you have to verify that "rawData" holds enough
bytes to populate the structure, or it'll copy garbage from the stack. If
you're lucky.
>

Marshal.PtrToSt ructure(pData, dr);

>
This shouldn't work, or at least, it doesn't for me. It throws
ArgumentExcepti on because "dr" is a structure. This overload is for classes;
for structures, the right syntax would be
>
DeadReckoning dr = (DeadReckoning) Marshal.PtrToSt ructure(pData,
typeof(DeadReck oning));
>
--
J.

My bad. I was trying to trim down the post. The DeadReckoning
structure is declared within a ExplicitLayout class (see below). The
explicit constructor outlines the call to marshalling data from an
array to the class structure.

namespace DIS
{
[StructLayout(La youtKind.Explic it)]
public class EntityState
{
[FieldOffset(0)]
public Header header; // 12 bytes

[FieldOffset(12)]
public EntityIdentifie r entityID; // 6 bytes

[FieldOffset(18)]
public ForceIdentifier forceID; // 1 byte

[FieldOffset(19)]
public byte numArticulation s; // 1 byte

[FieldOffset(20)]
public EntityType type; // 8 bytes

[FieldOffset(28)]
public EntityType altType; // 8 bytes

[FieldOffset(36)]
public Vector linearVelocity; // 12 bytes

[FieldOffset(48)]
public WorldCoordinate location; // 24 bytes

[FieldOffset(72)]
public EulerAngles orientation; // 12 bytes

[FieldOffset(84)]
public Appearance appearance; // 4 bytes

[FieldOffset(88)]
public DeadReckoning deadReckoning = new DeadReckoning() ; //
40 bytes

[FieldOffset(128 )]
public EntityMarking marking; // 12 bytes

[FieldOffset(140 )]
public Unsigned32 capabilities; // 4 bytes

[MarshalAs(Unman agedType.ByValA rray, ArraySubType =
UnmanagedType.S truct)]
[FieldOffset(144 )]
public Articulation[] articulations; // 16 bytes each

public EntityState() { }

public EntityState(byt e[] rawData)
{
// Copy the first 144 bytes to determine if there are
articulations.
unsafe
{
if (rawData.Length <= 144)
{
fixed (byte* pData = rawData)
{
Marshal.PtrToSt ructure((IntPtr ) pData, this);
}
}
else
{
int dataSize = rawData.Length 144 ? 144 :
rawData.Length;
IntPtr pData = Marshal.AllocHG lobal(dataSize) ;
Marshal.Copy(ra wData, 0, pData, dataSize);
Marshal.PtrToSt ructure(pData, this); // Throws
exception
Marshal.FreeHGl obal(pData);
}
}

// If there are articulations, allocate more memory for
this class
// and copy remaining data into articulations array.
if (rawData.Length 144 && numArticulation s 0)
{
// Allocate memory for articulations
articulations = new Articulation[numArticulation s];

// Copy values for each articulation
byte[] tempArray = new byte[16];
for (int i = 0; i < numArticulation s; i++)
{
Array.Copy(rawD ata, 144 + i * 16, tempArray, 0,
16);
unsafe
{
fixed (byte* pData = tempArray)
{
articulations[i] =
(Articulation)M arshal.PtrToStr ucture((IntPtr) pData,
typeof(Articula tion));
}
}
}
}

header.length = (ushort)rawData .Length;
}

public byte[] ToRaw()
{
int pduSize = (int) header.length;
byte[] byteArray = new byte[pduSize];
IntPtr pointer = Marshal.AllocHG lobal(pduSize);
Marshal.Structu reToPtr(this, pointer, false);
Marshal.Copy(po inter, byteArray, 0, pduSize);
Marshal.FreeHGl obal(pointer);
return byteArray;
}
}
}

Marshal Not Copying all Data to Fixed Byte Array

Marshal Not Copying all Data to Fixed Byte Array

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