MEX problem with mxGetData

Hi everyone !

I need advice to get this type of arguments:

• prhs[1] = {2, [5:12]}
• prhs[1] = {3, [ ], [1:5]}
• prhs[1] = {{4,6},[1:5], {1,8,9}, [3:6]} .

When I run the function I can find the good array with plhs[2] but I can't find the way to extract data, for further processing!

I know I have to use a pointer like mxGetData, but I'm trying every way except the good one I think !

if(nrhs==2)
     { 
      mxArray * extraits= mxDuplicateArray(prhs[1]);
      int n = mxGetN(extraits);
      double * a= (double*)mxGetData(extraits);

       /* Here, how can I find 2, and 5:12 for example ??? */

        plhs[2]=extraits;
       }

Thanks a lot !!!!

Answer 1

[James Tursa]

When you use the curly braces { } in MATLAB you are building a cell array, so you need to use mxGetCell in your mex routine. E.g.,

prhs[1] = {2, [5:12]}
prhs[1] = {3, [ ], [1:5]}
prhs[1] = {{4,6},[1:5], {1,8,9}, [3:6]}

In all of these cases you can get at the data as follows:

mxArray *cell;
double *pr;
mwSize i, j, n, ncell;
    :
if( mxIsCell(prhs[1]) ) {
    ncell = mxGetNumberOfElements(prhs[1]);
    for( i=0; i<ncell; i++ ) {
        cell = mxGetCell(prhs[1],i);
        if( mxIsEmpty(cell) ) {
            // Code to handle empty case
        } else {
            if( mxIsDouble(cell) {
                n = mxGetNumberOfElements(cell);
                pr = mxGetPr(cell);
                for( j=0; j<n; n++ ) {
                    // Code to manipulate pr[j] here
                }
            } else {
                // Code to handle non-double case
            }
        }
    }
}

Answer 2

[Kaustubha Govind]

Here, prhs[1] is a cell array, so you need to use mxGetCell to access elements of the cell array. You can then do a mxGetClassID query on each of the elements to determine how they should be handled. In your examples, the only expected types seem to be mxCELL_CLASS and mxDOUBLE_CLASS. For the former, you can recursively perform mxGetCell and examine the contents. For a double array, you can use mxGetData or mxGetPr to get the data.

Also, look at explore.c that the documentation for mxGetCell suggests as an example.

Answer 3

[Lea L]

thanks! it's perfect!