How to Convert a function return is a Handle (C++ mex)

Hi, I'm new to Matlab and looking for an example which demonstrates how to convert a function return is a Handle. (c++ mex)

C header, two function :

typedef void * DEVICE_HANDLE


DEVICE_HANDLE FUNC_CALL ZCAN_OpenDevice (UINT device_type, UINT device_index, UINT reserved);

mex:

void mexFunction(int nlhs,mxArray *plhs[],int nrhs, const mxArray *prhs[])

{

    typedef void * DEVICE_HANDLE;

    void *A;

    unsigned int C;

       if( nrhs != 3)

       {

              mexErrMsgTxt("MEXCPP requires 3 input arguments.");

              return;

       }

       nlhs=1;

 

    unsigned int p1 = mxGetScalar(prhs[0]);

    unsigned int p2 = mxGetScalar(prhs[1]);

    unsigned int p3 = mxGetScalar(prhs[2]);

    mexPrintf("%s%d\t%s%d\t%s%d\n", "P1: ", p1, "P2 :", p2,"P3 :",p3);

 

    plhs[0] = mxCreateNumericMatrix(1,1,mxUINT32_CLASS,mxREAL);

    A = (unsigned int *) mxGetPr(plhs[0]);

    C = (unsigned int)ZCAN_OpenDevice(p1,p2,p3);

    mexPrintf("%s%d\n", "return: ", C);

    A =C;

}

[James Tursa]

Please provide more details of what you are trying to do.

[huachun chen]

Hi,James. I've added some descriptions, trying to return a void pointers from mex functions.

Answer 1

[James Tursa]

DEVICE_HANDLE is a pointer, so if you are running 64-bit MATLAB then DEVICE_HANDLE will be be 64-bits and will not fit in a 32-bit unsigned int. Thus it seems that your code will lose information when you do the (unsigned int) cast.

To return the value of the (void *) back to MATLAB you could do something like this:

union { void *A;
        unsigned long long u;
      } Au;
unsigned long long *A;
      :
plhs[0] = mxCreateNumericMatrix(1,1,mxUINT64_CLASS,mxREAL);
A = (unsigned long long *) mxGetData(plhs[0]);
Au.A = ZCAN_OpenDevice(p1,p2,p3);
*A = Au.u;

But that begs the question, what are you intending to do with this pointer at the MATLAB level? I strongly suspect that you still have some fundamental design issues with your code that will lead to a crash.

[huachun chen]

Thank you for your reply, James.

It doesn't worked , I've tried to use the Load Library method, which is more concise, and work well.