我如何将其转换为c#(编组)

我有这些声明(DLL)，并试图将其转换为c#，以便我可以从DLL中调用函数。

struct1到struct3相同

typedef struct1  
{  
    int num;  
    char chars[25];  
    short shrt;  
    union  
    {  
         struct4 objstruct4;  
    }  
}  
typedef struct
{        
    Long Length;    
    short Type;    
    union    
    {
       struct1 objStruct1;      
       struct2 objStruct2;      
       struct3 objStruct3;    
    }Data;  
} Msg;

在c#中，我转换了这些…struct1到struct3也一样

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi, Pack = 1)]
public struct struct1  
{
    [MarshalAs(UnmanagedType.I4)]
    public Int32 num;  
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = size + 1)]
    public string chars;  
    [MarshalAs(UnmanagedType.I2)]
    public short shrt;  
    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi, Pack = 1)]
    public struct struct4
    {                
        [MarshalAs(UnmanagedType.Struct)]
        public ...
        ...
    }
[StructLayout(LayoutKind.Explicit, CharSet = CharSet.Ansi)]
protected struct Msg
{
    [FieldOffset(0)]
    [MarshalAs(UnmanagedType.I4)]
    public int Length;
    [FieldOffset(4)]
    [MarshalAs(UnmanagedType.I2)]
    public short Type;
    [FieldOffset(6)]
    [MarshalAs(UnmanagedType.Struct)]
    public Data MsgData;  
}
[StructLayout(LayoutKind.Explicit, Pack = 1, CharSet = CharSet.Ansi)]
public struct Data
{
    [FieldOffset(0)]
    [MarshalAs(UnmanagedType.Struct)]
    public struct1 objStruct1;      
    [FieldOffset(0)]
    [MarshalAs(UnmanagedType.Struct)]
    public struct2 objStruct2;      
    [FieldOffset(0)]
    [MarshalAs(UnmanagedType.Struct)]
    public struct3 objStruct3;    

}

问题是当我试图从DLL调用函数并将结构体MSG作为REF传递时，内部结构/联合(struct1到struct3)的一些成员变量没有值。就像它们在记忆中隆隆作响……

但是当我删除struct MSG中的struct1或struct2时，剩余内部结构/联合中的所有成员变量都被成功检索。

我可以问你的建议，如果我的转换是正确的还是我错过了什么…或者有没有更好的转换方法或者你知道为什么会出现这个问题。我怀疑的一件事是结构体(ANSI或Unicode)的大小，以及变量(结构体)的排列。

请告知-谢谢。

示例2:
////////////////

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct struct1  
{
    [MarshalAs(UnmanagedType.I4)]
    public Int32 num1;  
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = size + 1)]
    public string chars;
}
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct struct2 
{
    [MarshalAs(UnmanagedType.I4)]
    public Int32 num2;  
}
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct struct3 
{
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = size + 1)]
    public string chars;
    [MarshalAs(UnmanagedType.I4)]
    public Int32 num3;  
}
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct struct4
{
    [MarshalAs(UnmanagedType.I4)]
    public Int32 num4;  
    [MarshalAs(UnmanagedType.Struct)]
    public Data DataMsg;
    [StructLayout(LayoutKind.Explicit, CharSet = CharSet.Ansi)]
    public struct Data
    {
      //[FieldOffSet(0)]
      public struct1 str1;
      //[FieldOffSet(0)]
      public struct2 str2;
      //[FieldOffSet(0)]
      public struct3 str3;
    }
}
////////////////