C code not working inside MATLAB System

I'm trying to interface some C code inside a MATLAB system derived class. The C function I want to use multiplies by 3 the input argument. File "triple.h":

#ifndef __TRIPLE_H__
#define __TRIPLE_H__

#ifdef MATLAB_MEX_FILE
#include <tmwtypes.h>
#else
#include "rtwtypes.h"
#endif

double triple(double in);

#endif

File "triple.c":

#include "triple.h"

double triple(double in)
{
  return in*3;
}

I defined a MATLAB function "call_triple" so that I can call the C function. File "call_triple.m":

function out = call_triple(in)
%#codegen
assert(isa(in, 'double'));

if coder.target('MATLAB')
    out = call_triple_mex(in);
else
    out = double(0.0);
    out = coder.ceval('triple', in);
end

I compiled with the MATLAB coder "call_triple" to obtain "call_triple_mex":

>> codegen -config:mex call_triple triple.h triple.c

Now I can use call_triple from MATLAB command line:

>> call_triple(2.4)

ans =

      7.2000

Finally I implemented the class "triple_system"

classdef triple_system < matlab.System & coder.ExternalDependency
...
... more code
...
   function out = stepImpl(~, in)
      out = call_triple(in);
   end
...
... more code
...

The class works from the command line:

>> obj = triple_system;
>> step(obj, 3.2)

ans =

      9.6000

The problem arises when I use the class inside a "Matlab system" block inside Simulink and I select the option "Simulate using: code generation". The output of the Simulink block returns a number which makes no sense to me (like 1689233153 or similar big numbers). The block works fine when I select: "Simulate using: interpreted execution".

What am I doing wrong? I wold expect the same behaviour from the two simulation methods.

Thanks

Carlo

Answer 1

[Ryan Livingston]

You likely need to add coder.cinclude('triple.h') in the System Object to include the header for triple. Without the declaration of triple, the C compiler assumes that the signature is int triple(int) which results in the unexpected behavior that you are seeing.

[Carlo Savorgnan]

I added coder.cinclude('triple.h') inside the definition of call_triple and now it works.

Thank you!

[Ryan Livingston]

Glad to hear it, that's a hard error to track down.