Specifying inputs/outputs for C-code functions generated from MATLAB m-code using emlc as pass-by-reference

How do I make the generated c-code use pass-by-reference for all inputs and outputs instead of pass-by-value?

I am using emlc to generate c-code for a function that has constant, scalar, array (vector), and struct inputs and outputs. I am going to be calling this c-code from FORTRAN code, so I need to use pass-by-reference for all inputs and outputs. Depending on my FORTRAN compiler, I also may need to specify a calling convention. In the past, I have been writing wrappers for the generated code, which is tedious. How can I specify the interface that I want?

[James Tursa]

Can you show a short example, with code, to demonstrate the issue? How are you calling the emlc generated C code from Fortran?

[Todd]

Using A. Bottema's example below,

function y = foobar(a,b,c) %#eml

eml.cstructname(b, 'bstruct')

y = a + b.field1 + c(3);

I had been building as his example,

emlc -c -T rtw -d foobar -report foobar.m -eg { 0, struct('field1',0), zeros(3,1)}

and obtaining a c-function like:

real_T foobar(real_T eml_a, const bstruct eml_b, const real_T eml_c[3])

{

return (eml_a + eml_b.field1) + eml_c[2];

}

What I want is

void foobar(real_T *eml_a, const bstruct *eml_b, const real_T eml_c[3])

Then I can call it from FORTRAN:

CALL foobar(a,b,c)

provided I have defined the structure and array correctly.

A. Bottema's answer works, but is sort of a workaround. I still need a wrapper, but now I can write my wrapper in MATLAB. Or change how I use the function in MATLAB. It would be nice to just declare somehow what I want the interface to be...

Or, if there was a way to change how I call the function from FORTRAN...

[Todd]

Now the problem that I'm having is that two different functions create different versions of mldivide.c, so I can't put all of the object files in the same folder. If I try to put my wrapper functions all into one file and build that, they the function names get mangled.

Is there a way to define what the function name will be for a non-top-level function? Similar to the eml.cstructname function?

Answer 1

[Alexander Bottema]

To force call-by-reference for the top-level function you declare every input also as output.

Suppose you have the following function signature:

function y = foobar(a,b,c)

and you want call-by-reference on 'a', 'b' and 'c'.

Then add them as etra outputs:

function [y,a,b,c] = foobar(a,b,c)

For example:

function [y,a,b,c] = foobar(a,b,c) %#eml
y = a + b.field1 + c(3);

compiled with:

emlc -T RTW foobar.m -eg { 0, struct('field1',0), zeros(1,10) }

Will produce the C code:

real_T foobar(const real_T *a, const struct_T *b, const real_T c[10]) { return (*a + b->field1) + c[2]; }

As you can see the parameters 'a', 'b' and 'c' are now being passed by reference. In C arrays are always passed by reference so there are no need for using a pointer on that argument.

[Benjamin]

This is quite an old answer by now. Is it with newer Matlab releases still not possible to specifiy this explicitly with a coder or embedded coder configuration?

I'm currently dealing with similar issues and wouuld love to hear if I still need to handle this the same way as suggested here in 2011.