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

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huachun chen 2020-1-8

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/499463-how-to-convert-a-function-return-is-a-handle-c-mex

评论： huachun chen 2020-1-14

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;
}

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James Tursa 2020-1-9

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

huachun chen 2020-1-10

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

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Answer 1

James Tursa 2020-1-10

0
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/499463-how-to-convert-a-function-return-is-a-handle-c-mex#answer_409611

编辑：James Tursa 2020-1-10

在 MATLAB Online 中打开

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.