Problem using emxArray_real_T from Matlab Coder

Hi all,

I am trying to learn how to use standalone C++ code from Matlab. I have created a very simple function that takes only one argument, which is a vector of size (N,1), where N is unknown a priori. Therefore, I have to use dynamic allocated memory, if I am not wrong. The generated C++ code takes two arguments, of type emxArray_real_T, where x is the input vector, and yout the output vector,

void fun4(const emxArray_real_T *x, emxArray_real_T *yout)
{
   ...
}

Now, I am trying to create the input vector, and to run the function, but I think that I have no idea how to do it. I have read the answer in http://www.mathworks.com/matlabcentral/answers/67237-matlab-coder-segmentation-fault , but I think it is not so clear to me. This is what I am trying to do,

int main()
{
    double  datax[3];
    double  result[3] = {};

      emxArray_real_T *inputs, *outputs;

      for (int n=0; n<3; n++)
      {
          datax[n] = n;
      }

      inputs      = emxCreateWrapper_real_T(&datax, 1, 3);
      outputs     = emxCreateWrapper_real_T(&result, 1, 3);

      fun4(inputs, outputs);

      return 0;
  }

but I always get compilation errors,

   cannot convert ‘double (*)[3]’ to ‘real_T* {aka double*}’ for argument ‘1’ to ‘emxArray_real_T* emxCreateWrapper_real_T(real_T*, int32_T, int32_T)’

Since I am not an expert on C++, I was wondering if anyone can teach me how to pass the input vector, and to recover the results... Thank you very much in advance!

Answer 1

[Ryan Livingston]

Try using:

 emxCreateWrapper_real_T(datax, 1, 3)

The compiler is complaining because

 datax

is usually treated as a pointer to the first element of datax. Therefore

 &datax

is a pointer to an array of 3 doubles rather than a pointer to a single double as fun4 requires. This is the difference between

 double (*)[3] //pointer to array of 3 doubles

and

 double * //pointer to one double

[Carlos]

It worked!! Thank you very much! I thought I was driving crazy. Although, honestly, I was expecting something much more complicated... so now I feel a bit stupid :D As you can see, I am not really quite knowledgeable about C++ yet.

Answer 2

[Imran]

I have the same Issue

In my case I need to get out put as a Array of 2 rows and six column

so I am facing the the problem in line

outputs = emxCreateWrapper_real_T(data, 6, 2);

Could you please guide me.

I am currently running program as follows

int main()

{ double strem[12];

double data[2][6];

emxArray_real_T *inputs, *outputs;

for (int n=0; n<13; n++)

{

strem[n] = n;

}

inputs = emxCreateWrapper_real_T(strem, 1,12);

outputs = emxCreateWrapper_real_T(data, 6, 2);

charrang(inputs, outputs);

return 0;

}