如何将C ++ Struct与Union转换为C＃？

问题描述

我在调用DLL中的函数之后，在检索struct成员值时遇到困难。我试图将C ++代码转换为C＃，但我不知道如果它是否正确。请帮助我理解我在这里的错误（如果有）以及如何更正。

我的问题是我无法正确检索INNER STRUCTS ）我从DLL中调用ReceiveMessage函数。像例如m_objMsg.MsgData.StartReq.MsgID总是0.
但是当我尝试使用C ++ .exe程序时，MsgID有一个正确的值。 （非0）

C ++代码：

  extern int ReceiveMessage SESSION，int，Msg *）; 
 
 typedef struct 
 {
 char SubsId [15]; 
 int Level; 
 char选项[12]; 
} ConxReq; 
 
 typedef struct 
 {
 char MsgId [25]; 
} StartReq; 
 
 
 typedef struct 
 {
 long Length; 
 short类型; 
 union 
 {
 ConxReq oConxReq; 
 StartReq oStartReq; 
} Data; 
} Msg; 
 
 
 //////////////////////////////////////// /////////////// 
 Msg oMsg; 
 int rc = ReceiveMessage（Session，0，& oMsg）; 
 
 switch（rc）
 {
 case 0：
 switch（oMsg.Type）
 {
 case 0：// ConxReq 
 ... 
 break; 
 
 case 1：// StartReq 
 ... 
 break; 
 ... 
} 
  

这里是我试图将其转换为c＃

  [DllImport（MyDLL.dll，
 CallingConvention = CallingConvention.Cdecl，
 CharSet = CharSet .Ansi）] 
 protected static extern Int32 ReceiveMessage（IntPtr session，
 Int32 nTimeOut，
 [MarshalAs（UnmanagedType.Struct）] ref Msg ptrMsg）; 
 
 
 [StructLayout（LayoutKind.Sequential，CharSet = CharSet.Ansi）] 
 public struct ConxReq 
 {
 [MarshalAs（UnmanagedType.ByValTStr，SizeConst = 15）] 
 public string SubsId; 
 
 public Int32 Level; 
 
 [MarshalAs（UnmanagedType.ByValTStr，SizeConst = 12）] 
 public string选项; 
} 
 
 [StructLayout（LayoutKind.Sequential，CharSet = CharSet.Ansi）] 
 public struct StartReq 
 {
 [MarshalAs（UnmanagedType.ByValTStr， SizeConst = 25）] 
 public string MsgId; 
} 
 
 
 [StructLayout（LayoutKind.Sequential，CharSet = CharSet.Ansi）] 
 protected struct Msg 
 {
 public int Length ; 
 public Int16 Type; 
 public Data MsgData; 
} 
 
 StructLayout（LayoutKind.Explicit，CharSet = CharSet.Ansi）] 
 public struct Data 
 {
 [FieldOffset（0）] 
 public ConxReq oConxReq; 
 
 [FieldOffset（0）] 
 public StartReq oStartReq; 
} 
 
 
 Msg m_objMsg = new Msg（）; 
 m_objMsg.MsgData = new Data（）; 
 m_objMsg.MsgData.oConxReq = new ConxReq（）; 
 m_objMsg.MsgData.oStartReq = new StartReq（）; 
 
 int rc = ReceiveMessage（m_Session，nTimeOut，ref m_objMsg）; 
 
 
 then SWITCH条件
  

struct in the UNION for c ++ and c＃...
我有一个错误，说明...不正确对齐或... overlapped ...

c ++

  ConxNack oConxNack; 
 
 typedef struct 
 {
 
 int原因; 
 
} ConxNack; 
 
 
 [StructLayout（LayoutKind.Sequential）] 
 public struct ConxNack 
 {
 public int nReason; 
} 
 
 [FieldOffset（0）] 
 public ConxNack oConxNack;非常感谢您的时间和帮助... 
 b 
解决方案
 Akash是对的，看看这里： http://social.msdn.microsoft.com/Forums/en/csharplanguage/thread/60150e7b-665a-49a2-8e2e-2097986142f3  
 
 
 
另一个选项是创建两个结构体，并在知道它是哪个类型后使用适当的转换。
 
 
 
 hth 
 
 
 
马里奥
 
Guys I am having difficulties on retrieving struct member values after calling a function in the DLL. I tried to convert the C++ codes into C# but I’m not sure if it is correct or not. Please help me understand my mistakes here (if there is) and how to correct.

My problem here is I can’t correctly retrieved the values of the INNER STRUCTS (Union) after I called the ReceiveMessage function from the DLL. Like for example m_objMsg.MsgData.StartReq.MsgID is always 0.
But when I try to use the C++ .exe program, the MsgID has a correct value. (not 0)

C++ Code:  
extern int ReceiveMessage(SESSION, int, Msg*);

typedef struct
{
  char SubsId[15];
  int Level;
  char Options[12];
} ConxReq;

typedef struct
{
  char MsgId[25];
} StartReq;


typedef struct
{
  long Length;
  short Type;
  union
  {
    ConxReq oConxReq;
    StartReq oStartReq;
  } Data;
 } Msg;


/////////////////////////////////////////////////////
Msg oMsg;
int rc=ReceiveMessage(Session, 0, &oMsg);

switch(rc)
{
  case 0:
     switch(oMsg.Type)
     {
       case 0: // ConxReq
         …
         break;

      case 1: // StartReq
         …
         break;
   …
}
And here is my attempt to convert this into c#:  
[DllImport("MyDLL.dll",
  CallingConvention = CallingConvention.Cdecl,
  CharSet = CharSet.Ansi)]
  protected static extern Int32 ReceiveMessage(IntPtr session,
  Int32 nTimeOut,
  [MarshalAs(UnmanagedType.Struct)] ref Msg ptrMsg);


  [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
  public struct ConxReq
  {
     [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 15)]
     public string SubsId;

     public Int32 Level;

     [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 12)]
     public string Options;
  }

  [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
  public struct StartReq
  {
     [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 25)]
     public string MsgId;
  }


  [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
  protected struct Msg
  {
    public int Length;
    public Int16 Type;
    public Data MsgData;
  }

  StructLayout(LayoutKind.Explicit, CharSet = CharSet.Ansi)]
  public struct Data
  {
    [FieldOffset(0)]
    public ConxReq oConxReq;

    [FieldOffset(0)]
    public StartReq oStartReq;
  }


  Msg m_objMsg = new Msg();
  m_objMsg.MsgData = new Data();
  m_objMsg.MsgData.oConxReq = new ConxReq();
  m_objMsg.MsgData.oStartReq = new StartReq();

  int rc = ReceiveMessage(m_Session, nTimeOut, ref m_objMsg);


  then the SWITCH Condition
And If I add this struct inside the UNION for c++ and c#...I've got an error stating the "... incorrectly align" or "...overlapped..."
c++  
ConxNack oConxNack;

typedef struct
{

   int Reason;

} ConxNack;


[StructLayout(LayoutKind.Sequential)]
public struct ConxNack
{
    public int nReason;
}

[FieldOffset(0)]
public ConxNack oConxNack;
Thank you so much in advance for your time and help...
 解决方案 
Akash is right, have a look here: http://social.msdn.microsoft.com/Forums/en/csharplanguage/thread/60150e7b-665a-49a2-8e2e-2097986142f3
Another option is create two structs and use an appropriate cast once you know which type it is.
hth
Mario
                        
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