如何使用unsigned char *将结构从C＃传递到C ++？ [英] How to pass struct with unsigned char* from C# to C++?

问题描述

我有一些结构描述和一些方法的 C ++ dll ：

  struct MSG_STRUCT {
 unsigned long dataSize; 
 unsigned char * data; 
} 
  

并且功能例如：

$ b b

  unsigned long ReadMsg（unsigned long msgId，MSG_STRUCT * readMsg）
 {
 readMsg-> dataSize = someDataSize; 
 readMsg-> data = someData; 
} 
  

所以我想从 C＃

  [StructLayout（LayoutKind.Sequential）] 
 struct MSG_STRUCT 
 {
 UInt32 dataSize ; 
 byte [] data; 
} 
 
 [DllImport（mydll.dll）] 
 public static Int32 ReadMsg（UInt32 msgId，ref MSG_STRUCT readMsg）; 
  

所以我试图调用 C＃函数：

  var readMsg = new MSG_STRUCT（）; 
 readMsg.data = new byte [4128]; 
 Int32 res = ReadMsg（someMsgId，ref readMsg）; 
  

但我没有得到数据正常。
我也尝试使用 IntPrt 类型参数调用 ReadMsg ，但 Marshal。 PtrToStructure 有时给我 AccessViolationException 。

我没有任何想法如何将 MSG_STRUCT 的指针从 C＃传递到 C ++ ，并接收填充 MSG_STRUCT的结果。数据

最终解决方案对我有用：
我使用xanatos提供的解决方案的一部分：
我为我的DllImport函数设置 CallingConvention = CallingConvention.Cdecl 。
我发现我还需要更改：

  [MarshalAs（UnmanagedType.ByValArray，SizeConst = 4128） 
 public byte [] Data;感谢大家的帮助 
  你可以尝试：
  [StructLayout（LayoutKind。 Sequential）] 
 public struct MSG_STRUCT 
 {
 int dataSize; 
 IntPtr数据; 
 
 public byte [] GetData（）
 {
 var bytes = new byte [dataSize]; 
 Marshal.Copy（data，bytes，0，dataSize）; 
 return bytes; 
} 
} 
 
 [DllImport（NativeLibrary.dll，CallingConvention = CallingConvention.Cdecl）] 
 public static extern uint ReadMsg（uint msgId，ref MSG_STRUCT readMsg ）; 
  
，然后：
  MSG_STRUCT msg = new MSG_STRUCT（）; 
 uint res = ReadMsg（123，ref msg）; 
 byte [] bytes = msg.GetData（）; 
  
您的C函数重新分配数据指针，所以你必须把它回到C＃。最简单的方法（对我来说）是简单地传递 IntPtr 并做一些明确的 Marshal.Copy（...）。
 
 
 
另一种方法是使用 data  a  byte [] ，但是在C端你必须 memcpy（readMsg-> data，someData，someDataSize），而不是简单地赋值 readMsg- > data = someData 。
 
I have some C++ dll with struct description and some methods:
struct MSG_STRUCT {  
    unsigned long dataSize;
    unsigned char* data;
}
And function for example:
unsigned long ReadMsg( unsigned long msgId, MSG_STRUCT* readMsg)
{
    readMsg->dataSize = someDataSize;
    readMsg->data = someData;
}
So I want to call this function from C#:
[StructLayout(LayoutKind.Sequential)]
struct MSG_STRUCT 
{
    UInt32 dataSize;
    byte[] data;
}

[DllImport("mydll.dll")]
public static Int32 ReadMsg( UInt32 msgId, ref MSG_STRUCT readMsg);
So I tried to call C# function like:
var readMsg = new MSG_STRUCT();
readMsg.data = new byte[4128];
Int32 res = ReadMsg( someMsgId, ref readMsg);
But I didn't get smth normal in data.
I also tried to call ReadMsg with IntPrt type parameter, but Marshal.PtrToStructure gave me AccessViolationException sometimes.

I don't have any ideas how to pass a pointer to MSG_STRUCT from C# to C++ and receive the result as filled MSG_STRUCT.data

The final solutionthat worked for me:
I used a part of solution offered by xanatos:
I set CallingConvention = CallingConvention.Cdecl for my DllImport function.
I found out that I also need to change:
[MarshalAs(UnmanagedType.ByValArray, SizeConst = 4128)]
public byte[] Data;
Thanks everyone for your help
解决方案
You could try with:
[StructLayout(LayoutKind.Sequential)]
public struct MSG_STRUCT 
{
    int dataSize;
    IntPtr data;

    public byte[] GetData() 
    {
        var bytes = new byte[dataSize];
        Marshal.Copy(data, bytes, 0, dataSize);
        return bytes;
    }
}

[DllImport("NativeLibrary.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern uint ReadMsg(uint msgId, ref MSG_STRUCT readMsg);
and then:
MSG_STRUCT msg = new MSG_STRUCT();
uint res = ReadMsg(123, ref msg);
byte[] bytes = msg.GetData();
Your C function is reassigning the data pointer, so you have to marshal it back to C#. The easiest way (for me) is to simply pass a IntPtr and do some explicit Marshal.Copy(...).

An alternative is to have data a byte[], but then in C-side you have to memcpy(readMsg->data, someData, someDataSize)  instead of simply assigning readMsg->data = someData.

                        
这篇关于如何使用unsigned char *将结构从C＃传递到C ++？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！