issues in creating a mex file that uses as c++ object that works on complex<int32_t> data type...

Hi,

I am trying to create a mex file that uses a c++ object called my_chain. The c++ function process() uses inputs that are of complex<int32_t> data type.

So, I used mxComplexInt32 to declare my arrays. Though the mex file gets compiled, Matlab crashes when I try to run the mex routine.

Any help in this regard is appreciated.

Regards

surendra

PS: Please find attached my mex file..

#include <iostream>
#include <complex>
#include "stdlib.h"
#include "mex.h"
#include "my_chain.h"

using namespace std;

/* The gateway function */
void mexFunction(int nlhs, mxArray *plhs[],
int nrhs, const mxArray* prhs[])
{
    complex<int> *input_data, *output_data;
    
    int num_input_samples=0, num_output_samples=0, num_rows_out;
    int bw_MHz; // Operating bandwidth
    double f_rf_MHz; // RF frequency
    
    double rs_ratio;
    
    // Check for proper number of arguments
    if (nrhs != 4) {
        mexErrMsgIdAndTxt("MATLAB:mexcpp:nargin", "mexfn_rx_ds_chain requires four input arguments.");
        }
        if (nlhs != 1) {
            mexErrMsgIdAndTxt("MATLAB:mexcpp:nargout", "mexfn_rx_ds_chain requires two outputs argument.");
            }
            
            f_rf_MHz = mxGetScalar(prhs[0]);
            bw_MHz = mxGetScalar(prhs[1]);
            input_data = (complex<int> *)mxGetComplexInt32s(prhs[2]);
            num_input_samples = mxGetScalar(prhs[3]);
            
            rs_ratio = f_rf_MHz/bw_MHz;
            num_rows_out = (int)((double)num_input_samples/(32.0 * rs_ratio)) + 2;
            
            plhs[0] = mxCreateNumericMatrix(num_rows_out,1,mxINT32_CLASS, mxCOMPLEX);
            output_data = (complex<int> *)mxGetComplexInt32s(plhs[0]);
            
            // instantiate object
            my_chain object1(f_rf_MHz,bw_MHz);
            mexPrintf("f_rf_MHz is %f\n",f_rf_MHz);
            mexPrintf("num_input_samples is %d\n",num_input_samples);
            
            //Matlab crashes if I the below lines are executed.
            for(int ii=0; ii<20; ii++)
                {
                    mexPrintf("%d %d\n",input_data[ii].real(), input_data[ii].imag());
                    }
                
                num_output_samples = object1.process(input_data, num_input_samples, output_data);
                
                return;
                
                }

Answer 1

[Suman]

Hi Surendra,

From what I understand from the provided code snippet, the issue is that you are casting an mxArray data type to a C++ type, i.e., mxComplexInt32 to complex<int>. You should not do this casting and instead work with the mx data type.

Assuming you have an array of mxComplexInt32 type in prhs[2], you can do the following:

mxComplexInt32* input_data, *output_data;

input_data = mxGetComplexInt32s(prhs[2]); // this returns a pointer to the first element in the mxArray prhs[2]

for(int ii=0; ii<20; ii++) {

mexPrintf("%d %d\n",input_data[ii].real, input_data[ii].imag);

}

Please refer to these documentations to learn more about working with complex types in mxArray:

• https://in.mathworks.com/help/matlab/matlab_external/matlab-support-for-interleaved-complex.html
• https://in.mathworks.com/help/matlab/matlab_external/handling-complex-data-c.html

I hope that is helpful!

[Surendra Raju]

Thanks very much, Suman.