How to return array from imported C++ code in C function block in Simulink?

Hello everyone!

I am trying to import C++ code in Simulink through the C function block, for my purposes the block has 6 inputs type double, and 7 outputs type array of 9 doubles. I have been trying to run some dummy code in order to grasp how to use this block but I have been stuck for some time when trying to return an array from a C++ function and assigning it to the output array variable.

Here is the header file for the dummy class.

#pragma once
#include <vector>
#include <deque>
#include <array>
#include <cmath>
#include "mex.h"

class dummy{
    double x, y, psi, v, beta, dpsi;
    public:
    dummy(){}
    dummy(double x, double y, double psi, double v, double beta, double dpsi);
    double getX(){return x;}
    double getY(){return y;}
    double getPsi(){return psi;}
    double getV(){return v;}
    double getBeta(){return beta;}
    double getDPsi(){return dpsi;}
};
extern void createDrift(double x, double y, double psi, double v, double beta, double dpsi);
extern void deleteDrift();
extern mxArray* DriftOutput(double x, double y, double psi, double v, double beta, double dpsi)

And here is the source file.

#include <vector>
#include <deque>
#include <array>
#include "mex.h"
#include "dummy.h"

dummy* var;
dummy::dummy(double x, double y, double psi, double v, double beta, double dpsi){
    this->x = x;
    this->y = y;
    this->psi = psi;
    this->v = v;
    this->beta = beta;
    this->dpsi = dpsi;
}

extern void createDrift(double x, double y, double psi, double v, double beta, double dpsi){
    var = new dummy(x,y,psi,v, beta, dpsi);
}
extern void deleteDrift(){
    delete var;
}
extern mxArray* DriftOutput(double x, double y, double psi, double v, double beta, double dpsi){
    std::vector<double>vals(x,9);
    mxArray* temp = mxCreateNumericMatrix( 1, 9, mxSINGLE_CLASS, mxREAL );
     //memcpy( mxGetData(temp[0]), &vals[0], 9*sizeof(double) );
    /*temp.push_back(std::vector<double>(var->getX(),9));
    temp.push_back(std::vector<double>(var->getY(),9));
    temp.push_back(std::vector<double>(var->getPsi(),9));
    temp.push_back(std::vector<double>(var->getV(),9));
    temp.push_back(std::vector<double>(var->getBeta(),9));
    temp.push_back(std::vector<double>(var->getDPsi(),9));
    temp.push_back(std::vector<double>(var->getX(),9));*/
    return temp;
}

And this is the code from Output section of C function block

mxArray* temp = DriftOutput(x, y, psi, v, beta, dpsi);
xVec = temp;

Error that I get with this is

In line 3:error: 513, a value of type "mxArray *" cannot be assigned to an entity of type "real_T *"

| xVec = temp;

| ^

Has anyone encountered this problem before? Any tips on how to solve this?

I have tried to assign temp[0] to xVec, but that too ends in failure.

Answer 1

[Mark McBroom]

Why is your C++ code deailing with mxarray? The whole point of the C Function block is that behind the scenes it will generate wrapper code around your C++ code to handle transfer of data between Simulink and the C++ code ( which will likely involve using mxarray). I would recommend modifying your C++ code to remove the include of mxarray and rewrite your DriftOutput function.

Also, this link has tips for using the C Function block with C++ code.https://www.mathworks.com/help/simulink/ug/interface-with-c-classes-using-c-function-block.html