8 replies to this topic

[baxter]

Why is this not implemented? It means that we cannot run code like this,

[StructLayout(LayoutKind.Explicit)]
 struct UIntFloat 
    {        
         [FieldOffset(0)] <-- not implemented
        public float FloatValue; 

        [FieldOffset(0)] 
        public uint IntValue;         
    } 

public static float ToSingle(uint value) 
    { 
        UIntFloat uf = new UIntFloat(); 
        uf.IntValue = value; 
        return uf.FloatValue; 
    } 

public static uint ToUint(float value) 
    { 
        UIntFloat uf = new UIntFloat(); 
        uf.FloatValue = value; 
        return uf.IntValue; 
    }

It seems to be ignored or of very low priority,

http://netmf.codeplex.com/workitem/309

Also, does anyone know how to do this with the Micro Framework?

http://www.jasonbock...nsInDotNet.aspx

Baxter

[Mario Vernari]

The FieldOffset has only reason to exist for binary serialization, and native interop. However, for structs only. To tell the truth, it's over five years I'm using regular .Net, but I never used any interop or FieldOffset. Unions are not available too: if you wish some dirty trick, you'd use the "unsafe" context. The basic question is: why should I need similar features? The aim of the managed code is just to hide *any* potential dangerous/unsafe operation, such as unions and pointers. However, I agree on the lack of de/serialization APIs on Netduino. Cheers

[baxter]

The basic question is: why should I need similar features?

Well, I guess the reason is to create a union in C#
Baxter

[Mario Vernari]

Well, I guess the reason is to create a union in C#
Baxter

The question is right the same: why a C# programmer should need an union? That would be contrary to the C# type-safety base.

[baxter]

That would be contrary to the C# type-safety base

Hi Mario,
It is not. If you look at the code that I posted, the missing attribute simply allows a workaround for the missing Bitconverter functionality in the Micro Framework because it simulates a C union. Running the code in regular .NET C# (using System.Runtime.InteropServices;) gives,

static void Main(string[] args)
        {
            float a = 123.456f;
            uint b = ToUint(a); => 1123477881
        }

The integer is easily converted to an array of bytes. Note that there is no unsafe code at all (in Build, Allow unsafe code is unchecked), merely straight C#.

Baxter

[Mario Vernari]

Baxter, I mean what's your goal. I also agree that the BitConverter is a missing brick.
However, the conversion could be yielded even using the "unsafe". That is, there's no need of new statements: the language is really powerful by itself.
Take a look at this:
http://forums.netdui...ch__1#entry2082

[baxter]

Well Mario, This dialog is going nowhere. Why does a mountain climber climb a mountain? Answer: because it is there. This is not a new a statement request. There is also a Codeplex request. The statement is in regular C# and VB; just search MSDN. I have implemented Luke Cummings unsafe BitConverter as a DLL for use in both VB and C#. So, I guess the question is moot. Baxter

[Chris Walker]

Interesting. .NET MF is a subset of .NET (necessary to fit it on these small devices). That said, I always like seeing more features of the regular CLR making it to NETMF... Chris

[aalmada]

Unions are not available too: if you wish some dirty trick, you'd use the "unsafe" context.

"unsafe" is not officially supported: http://forums.netdui...ndpost__p__2151

Just like baxter, I used the "union" method several times in regular .NET. I tried this approach to avoid the "not-officially supported unsafe" and crashed into the same wall. StructLayoutAttribute is supported but FieldOffsetAttribute is not.

This is plain weird! .NET MF is a subset of .NET but for micro-processors. One of the basic required functionalities in this scenario is serial communication and, there is no official way to marshal floating points and structures... :-/

aalmada