Styjun

I am calling a C library from a C# code. The function I am calling take as parameter a struct containing arrays of struct :

 struct Example1Struct
 
 char* a;
 uint16_t b;
 AnotherStruct* c; 
 

c here is an array of pointer to AnotherStruct.

the struct in my C# code look like this

public struct Example1Struct
 
 public IntPtr StationName;//is char*
 public UInt16 IdCode;
 public IntPtr AnotherStruct; //array of struct AnotherStruct
 




public static IntPtr MarshalToPointer(object data)
 
 Type valueType = data.GetType();
 IntPtr buf = IntPtr.Zero;

 if (valueType.IsArray)
 
 if (data is char[])
 
 var d = data as char[];
 buf = Marshal.AllocHGlobal(Marshal.SizeOf(d.GetType().GetElementType()) * d.Length);
 
 else if (data is char[,])
 
 var d = data as char[,];
 buf = Marshal.AllocHGlobal(Marshal.SizeOf(d.GetType().GetElementType()) * d.Length);
 
 else
 
 buf = Marshal.AllocHGlobal(Marshal.SizeOf(data.GetType().GetElementType()) * count);

 long LongPtr = buf.ToInt64(); // Must work both on x86 and x64
 for (int I = 0; I < data.Lenght; I++)
 
 IntPtr RectPtr = new IntPtr(LongPtr);
 Marshal.StructureToPtr(data[I], RectPtr, false); // You do not need to erase struct in this case
 LongPtr += Marshal.SizeOf(typeof(Rect));
 

 

 return buf;
 
 else
 buf = Marshal.AllocHGlobal(Marshal.SizeOf(data));
 Marshal.StructureToPtr(data, buf, false);
 return buf;
 

my problem here is that I cannot cast data (who is an array of AnotherStruct) to object[] , neither in IEnumerable. So I cannot access to data[I] and don't have data.Lenght

Any idea ?

Usually I'd recommend using the MarshalAs attribute rather than writing manual marshalling code. It looks like:

public struct Example1Struct

 public IntPtr StationName;//is char*
 public UInt16 IdCode;
 public IntPtr AnotherStruct; //array of struct AnotherStruct

Could be:

public struct Example1Struct

 [MarshalAs(UnmanagedType.LPStr)]
 public string StationName;
 public UInt16 IdCode;
 [MarshalAs(UnmanagedType.LPArray)]
 public AnotherStruct[] OtherStructs;

And the marshaller should do the right thing for you when you pass it to unmanaged code.

You can get the length of the array like this:

if (data is Array a) 
 Console.WriteLine(a.Length);

Arrays in c# always derive from Array, so you can cast it to that.

But if possible in your real code, I'd recommend Damien's answer