See in the Modelica Specification:
https://modelica.org/documents/Modelica … ision1.pdf
12.9.1.2 Arrays

So basically there is written, that arrays are not possible. But i found there that structures / records are possible. But there is so little documentation about it. Can you  please help me ? There is a piece of code which I have in modelica
1 class

segway_vars vars;



  record segway_vars

    Real phi(start = 0);

    Real speedR(start = 0);

    Real speedL(start = 0);

    Real posR(start = 0);

    Real posL(start = 0);

  end segway_vars;



/// record is defined and initialised



// now there is a calling to external function

  function Get_outp

    input Real u1, u2;

    input Modelica.SIunits.Time simTime;

    /*input Real time;*/

    output segway_vars mystruct;

  

    external mystruct = ComunicationInterface(u1, u2, simTime) annotation(Library = "libgetref.o", Include = "#include \"Handle_data.h\"");

  end Get_outp;



//just equation part 

vars = Get_outp(u1, u2, time);

This is what i have done in openmodelica and compiling gets before calling external function(when i run it without libraries for my functions) so it should be ok i think.

The question is about C part(where i think problem lies). In documentation I have found out in 12.9.1.3 Records that Records are passed by reference (i.e. a pointer to the record is being passed).

So i created global structure in my header file

typedef struct segway_vars {

    double phi;

    double speedR;

    double speedL;

    double posR;

    double posL;

} seg_output;

seg_output * seg_output_p; 



double Get_reference_signal(double refval, int shkey);

seg_output *ComunicationInterface(double u1,double u2, double timesim);

double initTimetck(double);

And then I initialise memory fot it in function initTimettck which run only once on initial by

seg_output_p = malloc (sizeof (struct segway_vars));

And then I use it like this in function

seg_output *ComunicationInterface(double u1, double u2, double timesim) {



     //some not important code and then this 





    seg_output_p->phi=AT;

    seg_output_p->posL=0.2;

    seg_output_p->posR=0.3;

    seg_output_p->speedL=0.4;

    seg_output_p->speedR=0.5;

//(fixed values are just for testing for now)

    return seg_output_p;

}

Question is what have I done wrong? Complilation of simulation says:

Error: Error building simulator. Build log: clang   -fPIC -O0 -march=native   -g   -I"/usr/include/omc/c" -I. -DOPENMODELICA_XML_FROM_FILE_AT_RUNTIME  -c -o Segway.simulation.o Segway.simulation.c

clang   -fPIC -O0 -march=native   -g   -I"/usr/include/omc/c" -I. -DOPENMODELICA_XML_FROM_FILE_AT_RUNTIME  -c -o Segway.simulation_functions.o Segway.simulation_functions.c

Segway.simulation_functions.c:21:17: error: assigning to 'Segway_comunication__helper_segway__vars' (aka 'struct Segway_comunication__helper_segway__vars_s') from incompatible type 'seg_output *' (aka 'struct segway_vars *')

  _mystruct_ext = ComunicationInterface(_u1_ext, _u2_ext, _simTime_ext);

                ^ ~~~~~~~~~

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.

Or do you have any working example please? Thank you

Because records are passed by reference, you need to pass it as an input to the function and not return in.

@bumino: you can pass arrays as given in the specification. You need to pass them as input in the external functions (C references).

To: sjoelund.se
Thank you I now understand. I thought that meaning of passing the reference was about returning pointer. Now I understand that it is about changing the structure in function via passed reference I will try to do it this way.

To adrpo
I just needed to return 5 vals from my function. ( I dont exactly now if u meant that I should use same model as sjoelund.se proposed with structures but these structures I like more:) because it is defined better by var names:) )

Thank you both for help Have a nice week.

  ,

I looked into it more and a new problem arised. How should I declare this input structure in my code ? Which type it should be? I tried to build exactly same structure as was pointed out in documentation, but it does not work (in structure/record mapping there is really too few written about it)

Error: Error building simulator. Build log: clang   -fPIC -O0 -march=native   -g   -I"/usr/include/omc/c" -I. -DOPENMODELICA_XML_FROM_FILE_AT_RUNTIME  -c -o Segway.simulation.o Segway.simulation.c
clang   -fPIC -O0 -march=native   -g   -I"/usr/include/omc/c" -I. -DOPENMODELICA_XML_FROM_FILE_AT_RUNTIME  -c -o Segway.simulation_functions.o Segway.simulation_functions.c
Segway.simulation_functions.c:21:45: error: passing 'Segway_comunication__helper_segway__vars' (aka 'struct Segway_comunication__helper_segway__vars_s') to parameter of incompatible type 'struct segway_vars *'
  _goon_ext = ComunicationInterface(_u_ext, _inpstruct_ext, _simTime_ext);
                                            ^~~~~~~~~~~~~~
./Handle_data.h:18:56: note: passing argument to parameter 'seg_output_p' here
int ComunicationInterface(double u,struct segway_vars *seg_output_p, double timesim);


in C code

struct segway_vars {

    double phi;

    double speedR;

    double speedL;

    double posR;

    double posL;

};
in OM

  record segway_vars

    Real phi(start = 0);

    Real speedR(start = 0);

    Real speedL(start = 0);

    Real posR(start = 0);

    Real posL(start = 0);

  end segway_vars;

There is really not an example? It would have explained a lot         

Can you please help me and tell me how to declare structure in C header file so it would be compatibile with OpenModelica?

Because I wont compile a file without it and then a collision occurs as in post above.

I also tried it with arrays

I can read from array, but when I try to write to array segmentation fault occurs

Also documenations says that there is size_t with length about array but there is not.


Found the core of the problem

one have to call it like this :::
function foo
input Real a[:,:,:];
output Real x;
external;
end foo;

and not

function foo2
input Real a[:,:,:];
output Real x;
external x=foo(a);
end foo2;