equivlaent use of union in C

equivlaent use of union in C

• RayCan

  The code you posted work fine for me. The error is apparently elsewhere in the code.

  Try post a short-but-complete program (http://yoda.arachsys.com/csharp/complete.html) which shows the error.

  
  
  

• Andy P.

  public DataType(string dstring, int dint, float dfloat, double ddouble, char dchar)
  {
  this.Dstring = dstring;
  this.Dint = dint;
  this.Dfloat = dfloat;
  this.Ddouble = ddouble;
  this.Dchar = dchar;
  }

  That's not going to work. dfloat will overwrite what's in Dint. ddouble will overwrite what's in Dfloat. Then finally Dchar will overwrite what's in Ddouble. Leaving Dchar the only correct value.

  
  

  
  
  

• Jassim Rahma

  StructLayout(Layoutkind.Explicit] won't work for strings. I replaced explicit and has a precise offset value with sequential layout. Explicit layouts are not permitted with reference types like the String in the example code.

  [StructLayout(LayoutKind.Sequential)]
  public struct DataType
  {
  [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 16)] public String Dstring;
  [MarshalAs(UnmanagedType.I4)] public int Dint;
  [MarshalAs(UnmanagedType.R4)] public float Dfloat;
  [MarshalAs(UnmanagedType.R8)] public double Ddouble;
  [MarshalAs(UnmanagedType.U1)] public byte Dbyte;
  public DataType(String dstring, int dint, float dfloat, double ddouble, byte dbyte)
  {
  this.Dstring = dstring;
  this.Dint = dint;
  this.Dfloat = dfloat;
  this.Ddouble = ddouble;
  this.Dbyte = dbyte;
  }
  }

  public struct XMLData
  {
  public string Tag;
  public DataType Item;
  public XMLData(string tag, DataType item)
  {
  this.Tag = tag;
  this.Item = item;
  }
  }

  public XMLData xmldata = new XMLData();

  public LinkedList<XMLData> LL = new LinkedList<XMLData>();
  public LinkedListNode<XMLData> LLN;

  
  

• Sylvia msdn forum

  Error is..... TypeLoad Exception unhandled

  Could not load type 'DataType' from assembly 'WinTest, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' because it contains an object field at offset 0 that is incorrectly aligned or overlapped by a non-object field.

  Code Example:

  using System;
  using System.Collections.Generic;
  using System.ComponentModel;
  using System.Data;
  using System.Drawing;
  using System.Text;
  using System.Windows.Forms;
  using System.Runtime.InteropServices;

  namespace WinTest
  {
  public partial class Form1 : Form
  {
  
  [StructLayout(LayoutKind.Explicit)]
  public struct DataType
  {
  [FieldOffset(0)]
  public string Dstring;
  [FieldOffset(0)]
  public int Dint;
  [FieldOffset(0)]
  public float Dfloat;
  [FieldOffset(0)]
  public double Ddouble;
  [FieldOffset(0)]
  public char Dchar;
  public DataType(string dstring, int dint, float dfloat, double ddouble, char dchar)
  {
  this.Dstring = dstring;
  this.Dint = dint;
  this.Dfloat = dfloat;
  this.Ddouble = ddouble;
  this.Dchar = dchar;
  }
  }
  public DataType DType = new DataType();
  public struct XMLData
  {
  public string Tag;
  public DataType Item;
  public XMLData(string tag, DataType item)
  {
  this.Tag = tag;
  this.Item = item;
  }
  }

  XMLData xmldata;
  LinkedList<XMLData> LL;
  
  public Form1()
  {
  InitializeComponent();
  }

  private void Form1_Load(object sender, EventArgs e)
  {
  xmldata = new XMLData("", DType);
  LL = new LinkedList<XMLData>();
  LL.AddLast(xmldata);
  }
  }
  }

  
  
• equivlaent use of union in C