Sending struct with dyamic array of string to c++ dll from c#

Question

I have a struct defined as

struct DiskInfo{
int size,
char **atributes
};

I need to sent it to c++ dll that will run something like

for(i=0;i<Files.count;i++)
{
   newList[i] = (wchar_t *)malloc(sizeof(List->Strings[i]));  
   wcscpy(newList[i], List->Strings[i]);
  .... more code
 }

At this point I have the struct poplutaed will all the data, and i need to send it back to c#. I tried:

internal struct DiskInfo
    {
        internal int size;
        [MarshalAs(UnmanagedType.ByValArray)]
        internal string[] Files;
    }

and the signature is

[DllImport("Disk.dll", CallingConvention = CallingConvention.Cdecl, EntryPoint = GetDiskInfo")]
    internal static extern uint GetDiskInfo(
       [In, Out] 
        DiskInfo Param);

And call to function

 data= new DiskInfo();
 Native.GetDiskInfo(data);

However, data is always returned as null. What am I doing wrong?

I'm confused. The C++ and C# structs shown here have different names, different member order, and the C++ version doesn't contain a "ByVal" array. Are these supposed to be the same structs? — Sven
– Sven, Commented Jul 15, 2011 at 9:18

Kevin Watkins · Accepted Answer · 2011-07-15 22:08:15Z

1

In C#, DiskInfo is a struct, which means that it is a value type, and will be passed into a method by copying (unless the ref keyword is used). So the C++ code can't possibly modify the original struct, only the copy. You might have better luck if you declared GetDiskInfo with the ref keyword and also used that keyword in your method call.

answered Jul 15, 2011 at 22:08

Kevin Watkins

1111 silver badge1 bronze badge

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Sending struct with dyamic array of string to c++ dll from c#

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related