Labview Calling DLL with 2D array input and output

Question

Hi all，
    I have to call  a dll which a 2D double array as an input and also a 2D double array as an output.The dll is made by me and written in c language , I need it to work  efficiently.
If i define the program in labview like this
The 2 2Darrays sent into CLN were "Array data pointer",then how to define the function in c laguage? just like  -----int  myfunction (Parameter1,Parameter2,Parameter3,Parameter4)
If the function in the dll is defined like this         int myfunction (double  **A, int sx,int sy ,double **B,int ix,int iy),then what will the program in labview will be ?
sx ,sy ix ,iy are the array's size.

Answer 1

ylongwu wrote:
If the function in the dll is defined like this         int myfunction (double  **A, int sx,int sy ,double **B,int ix,int iy),then what will the program in labview will be ?
sx ,sy ix ,iy are the array's size.
Your proposed prototype double ** seems to indicate that you want an array of pointers to the rows of the array. That is not how LabVIEW stores multidimensional arrays (nor how this is usually done in C for such arrays).
LabVIEW and most C libraries threat multi dimensional array as one single block of memory where the rows are located one after the other. So as DFGray has already pointed out you should use double * instead as datatype or since you create the DLL yourself and if it doesn't need to be compatible with other environments than LabVIEW change that altogether into:
typedef struct {
   int32 dimSize1;
   int32 dimSize2;
   double elm[1];
} 2DDblArrRec, **2DDblArrHdl;
int myfunction (2DDblArrHdl A, 2DDblArrHdl B);
then change the Call Library Node parameters for the arrays to pass the array as Data Handle (the native LabVIEW datatype) and leave away the extra dimensions since they are already inside the handle structure.
Last but not least if you want to be very fancy you can even use NumericArrayResize() on the output handle to resize it to the correct size before filling in your information and leave away the Initialize Array function on the LabVIEW diagram.
Message Edited by rolfk on 05-26-2010 09:11 AM
Rolf Kalbermatter
CIT Engineering Netherlands
a division of Test & Measurement Solutions