C# control the alignment of data

Question

In C++ you can use __declspec( align( # ) ) declarator to control the alignment of user-defined data. How can do this for C#. I have two procedures written on Assembler in my dll. Arguments for procedures (two arrays) should be aligned on 16 bytes. For C++ it works fine.

I just used declarations

__declspec( align( 16 ) )
double a[2]={10.2,10.6};

Loreenlorelei

maybe you should tell us what you want to do rather than (or in addition to) how you would do it in another language. – Gorgon

@Servy: Quite frankly I thought he was pretty clear as to what he wants to do; providing an example in a different language is normal. – Kanpur

@ChrisLively It's not wrong, I just don't consider it sufficient. You limit responses to people who are familiar with the functionality of the other language. A direct port also isn't always idea between languages. If the underlying problem is know a solution more appropriate to the language may be used. – Gorgon

Answer 1

If you are looking for managed to non-managed interop (transmitting data between C#/.NET-based and C/C++/assembler-based software), you would use a combination of the StructLayout attribute and the FieldOffset attribute:

[StructLayout(LayoutKind.Explicit, Pack = 16)]
public class MyDataClass {
    [FieldOffset(0)]
    double[] a;
}

According to MSDN:

The System.Runtime.InteropServices.StructLayoutAttribute.Pack field determines the memory alignment of data fields of a target object.

https://learn.microsoft.com/en-us/dotnet/api/system.runtime.interopservices.structlayoutattribute.pack

Katheryn

learn.microsoft.com/en-us/dotnet/api/… is the updated link for documentation – Vella

Answer 2

Contrary to the other answer, you do not need LayoutKind.Explicit, you just need Pack. You therefore don't need FieldOffset either.

You probably also want a struct not a class.

[StructLayout(LayoutKind.Sequential, Pack = 16)]
public struct MyDataClass
{
    double[] a;
}

Note that this only helps for interop code, it will not help for managed code.

Headsman