mex : return c struct member value to matlab struct member

I understand that in order to pass the matlab struct(and return), these are the steps to follow:

1)Do an iteration through matlab struct to copy to my C struct.

2)Make a copy of the matlab struct (for llhs, since we cant change anything of prhs)

3)run the c subroutine

4)after running the c subroutine, the changes made to the C struct members are copied to the new matlab struct(created in step2)

I have done steps 1-3 using the phonebook example, but I have no idea how to copy the value from the modified C struct back to the matlab struct. I have tried the function below but it does not make changes:

Let's say my C struct is as below:

typedef struct{ double a; double b; }mycstruct_type

my mex function: void mexFunction( int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[] ) {

   ..copy prhs matlab struct to c struct
   ..make a copy of prhs to plhs[0]  

    /*this section below try to make changes in c struct to matlab struct */

    mxArray *mat_a = mxCreateDoubleMatrix(1, 1, mxREAL);
    double *ptr;
    ptr=mxGetPr(mat_a);
    ptr=&mycstruct.a;

    dummyCfunction(&mycstruct);

    mxSetField(plhs[0],0,"a",mat_a);

    return

}

the dummyCfunction will make changes to mycstruct.a and I want this changes to be reflected back at the matlab struct field (a) in plhs[0]. How do I do that?

Answer 1

[James]

Hmm not sure why the answer got deleted. Thanks Friedrich, I managed to solve with your suggestion.

Answer 2

[Ping]

I have the same problem to solve. Can you re-post the answer?