将C ++结构转换为C＃结构

Question

I need to convert a struct to bytes so that I can send or receive it over a network.

Let's say the struct is something like below:

struct Info
{
    unsigned int Age;
    char Name[];
};

I have the equivalent struct in C# sharp which is:

[StructLayout(LayoutKind.Sequential)]
public struct Info
{
    public uint Age;
    public string Name;
};

To convert the C# struct to byte I use the this method:

    public Byte[] GetBytes(Info info)
    {
        int size = Marshal.SizeOf(info);
        byte[] arr = new byte[size];
        IntPtr ptr = Marshal.AllocHGlobal(size);

        Marshal.StructureToPtr(info, ptr, true);
        Marshal.Copy(ptr, arr, 0, size);
        Marshal.FreeHGlobal(ptr);

        return arr;
    }

And to Convert the received bytes to C++ struct I use this method:

Info GetInfo(const char* bytes)
{
    Info info;
    memcpy(&info, bytes, sizeof(info));

    return info;
}

My problem is that the Age field of the struct converts very well but the Name field never is what has been sent.

Update

I can easily convert a string to bytes using the code below and send it from c# client app to c++ server app.

        byte[] buffer = Encoding.UTF8.GetBytes(text + "\0");

so I decided to change the C# struct as below:

[StructLayout(LayoutKind.Sequential)]
public struct Info
{
    public uint Age;
    public byte[] Name;
};

but in this case the GetBytes() method crashes.

Answer 1

1. Your C++-structure uses a flexible array member as the last element, which is an extension borrowed from C99:

   In essence, it means that an array of unknown length ends it.
   Because the length is not known, the compiler will, when asked for the structures size, assume 0 .
   I somehow doubt that's what you wanted.

2. Your C#-structure has a string -member, which is not a value-type.

   Just copying the managed pointer to it like you do is quite nonsensical.

So, what should you do?

Define your own wire-format.

• An unsigned 32-bit integer will be easily marshalled.

• The string is more difficult. Do you have a sentinel-value never part of the string?
  Or do you have to use / prefer counted strings, in which case you have to decide what type the size will be and marshal that first?

  Also, don't forget the character-set: Prefer UTF-8, though if it's windows-only, UTF-16 little-endian may also be a viable choice.

Answer 2

This can get very complicated very quickly.

You might want to look at some libraries that can help - Google Protobuf and Apache Thrift immediately spring to mind. Both support C++ and C# amongst other languages.