.net - 从 .NET 为非原始数据类型调用旧的 C++ 函数

Question

我有一个旧的 C++ 函数，我必须在我的 .NET 应用程序中使用它。每次我尝试调用并将指针转换回类时，我都会收到一条错误消息，指出我试图读取或写入 protected 内存。请有人帮我指出正确的方向。这是代码:

typedef struct
{
 char szModel[32];
 float fSpeed;
 float fData[20];
} CAR, far *LP_CAR; 

//Function prototype
int FAR PASCAL Process(char szModel[32], LP_DATA pCar); 

还有我的 .NET 代码:

[DllImport("Unmanaged.dll", CharSet = CharSet.Ansi)]
public static extern int Process(string model, IntPtr data);

//****** Implementation **********

public class ManagedClass
{
   public string szModel = new string(new char[32]);
   public float fSpeed;
   public float[] fData = new float[20];
}

ManagedClass aCar = new ManagedClass();
IntPtr ptr = Marshal.AllocHGlobal(Marshal.Sizeof(aCar));
Marshal.StructureToPtr(aCar, ptr, false);
Process(aCar, ptr);

ManagedClass model2 = (ManagedClass)Marshal.PtrToStructure(ptr, 
                                                           typeof(ManagedClass));

Answer 1

我会这样做:

C++

typedef struct
{
  char szModel[32];
  float fSpeed;
  float fData[20];
} CAR, far *LP_CAR; 

extern "C" {
    int __stdcall Process(char *szModel, CAR &lpCar); 
}

C#

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
struct CAR
{
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 32)]
    public string szModel;
    float fSpeed;
    [MarshalAsAttribute(UnmanagedType.ByValArray, SizeConst = 20)]
    float[] fData;
}

[DllImport("Unmanaged.dll", CharSet = CharSet.Ansi)]
static extern int Process(
    string model, 
    ref CAR data
);

调用如下:

CAR data;
Process(@"test", ref data);