How to import a C++ function with int and double parameters

Question

I am trying to import a C++ function in my C# code.

This function is defined as:

int SetPointers(int* ID, int* BufferID, int** Pointer, double** Time, int NumberOfPointers);

with ID an array of int, BufferId an array of int, Pointer an array of int, Time an array of double, and NumberOfPointers an int.

I have tried to use IntPtr without success.

Here is the latest code I tried:

[DllImport("open.dll", SetLastError = true, CharSet = CharSet.Auto, CallingConvention = CallingConvention.Cdecl)]
public unsafe static extern int SetPointers(int* ID, int* BufferID, ref IntPtr Pointer, ref IntPtr Time, int NumberOfPointers);
public unsafe int _SetPointers(int[] ID, int[] BufferID, ref int[] Pointer, ref double[] Time, int NumberOfPointers)
{
    IntPtr fQueue = IntPtr.Zero;
    IntPtr fTime = IntPtr.Zero;
    int breturn = -1;
    fixed (int* fId = ID)
    fixed (int* fBufferID = BufferID)
    fQueue = Marshal.AllocHGlobal(Marshal.SizeOf(typeof(int)) * Pointer.Length);
    fTime = Marshal.AllocHGlobal(Marshal.SizeOf(typeof(double)) * Timestamp.Length);
    breturn = SetPointers(fId, fBufferID, ref fQueue, ref fTime, NumberOfPointers);
    return breturn;
}

How can I do this?

You need to show, how this function is used in unmanaged code. Or show the function code. — Alex F
– Alex F, Commented Nov 26, 2013 at 15:54
I can't modify that code, and it is very complex. Basically, ID, BufferId and NumberOfPointers are only read by the function and Pointer and Time are like returned values. Does this help? — diditexas
– diditexas, Commented Nov 26, 2013 at 15:55
I dont think you are doing the right thing. Double referencing is probably an out parameter - Please read this stackoverflow.com/questions/6810419/… — Sujay Ghosh
– Sujay Ghosh, Commented Nov 26, 2013 at 16:05

Peter Mortensen · Accepted Answer · 2022-05-30 19:40:09Z

2

First all, you might want to use IntPtr for your parameters rather than int[].

After this, I haven't tried it but to marshal pointers on pointers a "ref IntPtr" or "out IntPtr" would work.

public unsafe int _SetPointers(IntPtr ID, IntPtr BufferID, ref IntPtr Pointer, ref IntPtr Time, int NumberOfPointers);

Also have a look to this other question: How do I marshall a pointer to a pointer of an array of structures?

edited May 30, 2022 at 19:40

Peter Mortensen

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answered Nov 26, 2013 at 15:58

DarkUrse

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1 Comment

David Heffernan Over a year ago

First two parameters are fine as arrays

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