Struct - Layout.Explicit - Constructor - fully assign fields

Question

Why if i use:

struct MyStruct
{
        [FieldOffset (0)] public uint Data;
        [FieldOffset (0)] public byte Something;
}

public MyStruct (uint pData)
{
   Data = pData; // setting Data field also sets Something field
}

C# says i need to assign 'Something' field :/ I know I can do a "Constructor : this ()" but compiler should know 'Data' field contains 'Something' field.

So, I should call parameterless constructor first, is it the only way?

Hollis

Answer 1

Yes, you'll need to call the default constructor.

public MyStruct (uint pData) : this()
{
   //...
}

The compiler will then generate the following IL instructions at the beginning of your constructor:

ldarg.0           // Push address of struct onto stack
initobj MyStruct  // Pop address of struct and initialize it with "all zeros"

Vienne

This is very useful. Doing this speeds up the code by one or more nanoseconds (depending on how many fields are). – Pulsar

Answer 2

Seems like it is not possible, and the discussion about it has been closed down:

Here is a link to the discussion regarding this issue:

https://github.com/dotnet/roslyn/issues/7323

Mariselamarish

Answer 3

You need to initialize all of the fields of a struct if you define a custom constructor. See this MSDN tutorial in structs for more information - specifically under the Constructors and Inheritence heading.

Here is an paragraph extracted from that link with regards to this:

Structs can declare constructors, but they must take parameters. It is an error to declare a default (parameterless) constructor for a struct. Struct members cannot have initializers. A default constructor is always provided to initialize the struct members to their default values.

Monty

I'm talking about something else. – Hollis

@zgnilec In that case I would suggest reviewing your question as it doesn't make a lot of sense. – Monty

Well, maybe someone else will understand me. – Hollis