获取从本机dll到c#应用程序的结构数组

Question

我有一个C#.NET 2.0 CF项目,我需要在本机C++ DLL中调用一个方法.此本机方法返回一个类型的数组TableEntry.在调用本机方法时,我不知道数组的大小.

如何从原生DLL到C#项目获取表？以下是我现在所拥有的.

// in C# .NET 2.0 CF project
[StructLayout(LayoutKind.Sequential)]
public struct TableEntry
{
    [MarshalAs(UnmanagedType.LPWStr)] public string description;
    public int item;
    public int another_item;
    public IntPtr some_data;
}

[DllImport("MyDll.dll", 
    CallingConvention = CallingConvention.Winapi, 
    CharSet = CharSet.Auto)]
public static extern bool GetTable(ref TableEntry[] table);

SomeFunction()
{
    TableEntry[] table = null;
    bool success = GetTable( ref table );
    // at this point, the table is empty
}


// In Native C++ DLL
std::vector< TABLE_ENTRY > global_dll_table;
extern "C" __declspec(dllexport) bool GetTable( TABLE_ENTRY* table )
{
    table = &global_dll_table.front();
    return true;
}

谢谢,PaulH

Answer 1

当编组从原生到托管的未知大小的数组时,我发现最佳策略如下

• IntPtr在托管代码中键入数组
• 让本机代码返回数组和size参数.
• 手动将数据封IntPtr送到托管端的自定义结构.

因此,我会对您的代码进行以下更改.

本机:

extern "C" __declspec(dllexport) bool GetTable( TABLE_ENTRY** table, __int32* pSize )
{
    *table = &global_dll_table.front();
    *pSize = static_cast<int32>(global_dll_table.size());
    return true;
}

管理:

[DllImport("MyDll.dll", 
    CallingConvention = CallingConvention.Winapi, 
    CharSet = CharSet.Auto)]
[return: MarshalAs(UnmanagedType.I1)]
public static extern bool GetTable(out IntPtr arrayPtr, out int size);

public static List<TableEntry> GetTable() {
  var arrayValue = IntPtr.Zero;
  var size = 0;
  var list = new List<TableEntry>();

  if ( !GetTable(out arrayValue, out size)) {
    return list; 
  }

  var tableEntrySize = Marshal.SizeOf(typeof(TableEntry));
  for ( var i = 0; i < size; i++) {  
    var cur = (TableEntry)Marshal.PtrToStructure(arrayValue, typeof(TableEntry));
    list.Add(cur);
    arrayValue = new IntPtr(arrayValue.ToInt32() + tableEntrySize);
  }
  return list;
}