[Mono-list] Marshal.SizeOf() vs. sizeof operator

[Giuseppe Greco]

>-- Original Message --
>From: Marcus <mathpup@mylinuxisp.com>
>To: "Giuseppe Greco" <gius.greco@bluewin.ch>
>Subject: Re: [Mono-list] Marshal.SizeOf() vs. sizeof operator
>Cc: mono-list@ximian.com
>Date: Wed, 13 Aug 2003 00:17:17 -0500
>
>
>I think that you're using Marshal.SizeOf() in a way that is not intended.
>It 
>appears that this method is mainly useful when invoked on classes or structs
>
>that will undergo marshalling conversions when passed to P/Invoke methods.
>I 
>don't think that it was intended to be invoked on enums.
>
>What are you attempting to do where the size of the unmanaged struct makes
>a 
>difference?

Let's analyze anoter example:

char myChar = 'A';
Console.WriteLine("myChar is of type {0}", c.GetType());

The code above should produce the message

  "myChar is of type System.Char"

Well, with Mono on Linux I get the right type name, while
with .NET on Windows I get

  "myChar is of type System.Byte[]"

Do you see the problem?

Gius_.

>
>
>
>On Tuesday 12 August 2003 10:59 pm, Giuseppe Greco wrote:
>> Marcus,
>>
>> here's an example:
>>
>> public enum FieldType : byte
>> {
>>     Undefined = 0,
>>     Int16,
>>     Int32,
>>     Int64
>> }
>>
>> Then, try something like this:
>>
>> using System;
>> using System.Runtime.InteropServices;
>>
>> public class MyClass
>> {
>>     private FieldType fieldType = FieldType.Undefined;
>>
>>     public void MyMethod()
>>     {
>>         Console.WriteLine("The size of fieldType is {0}",
>>             Marshal.SizeOf(fieldType.GetType());
>>     }
>> }
>>
>> The code above executes sucessfully with Mono on Linux,
>> but it doesn't with .NET on Windwos, where I always get
>> the following exception:
>>
>> Unhandled Exception: System.ArgumentException:
>> Type FieldType can not be marshaled as an unmanaged
>> structure; no meaningful size or offset can be computed.
>> at System.Runtime.InteropServices.Marshal.SizeOf(Type t)
>>
>> Rewriting MyMethod like this
>>
>>     public void MyMethod()
>>     {
>>         Console.WriteLine("The size of fieldType is {0}",
>>             Marshal.SizeOf(Type.GetType("System.Byte"));
>>     }
>>
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