Passing array in struct by reference to coder.ceval

Question

I have a struct with very large arrays in it. I use MATLAB coder to generate C code.
In my generated code I wish to call some C function and pass by reference one of the arrays.

For example:

coder.ceval('Foo',coder.ref(MyStruct.VeryLargeArray));

This is not allowed by MATLAB coder and I get the error:

coder.ref may only be applied to an expression of the type V or V(E) ...

Since MyStruct.VeryLargeArray is very large, as the name suggests, I wish to avoid the abvious solution of copying it to a temporary varliable:

UnnecessaryTempVar = MyStruct.VeryLargeArray;
coder.ceval('Foo',coder.ref(UnnecessaryTempVar));  

Any ideas for a workaround?

Answer 1

You could write a C wrapper for Foo that accepts a pointer to a struct and forwards the underlying data pointer, MyStruct->VeryLargeArray, to Foo.

MATLAB Code passStruct.m:

function y = passStruct(x)
%#codegen
coder.cinclude('Foo.h');
s.f = x;
coder.cstructname(s, 'wrapperStruct_T');
y = 10;
y = coder.ceval('WrapFoo', coder.ref(s));

Header file Foo.h:

/* Include generated header to get struct definition */
#include "passStruct.h"
double WrapFoo(wrapperStruct_T *s); 
double Foo(double *x);

Source file Foo.c:

#include "Foo.h"
double WrapFoo(wrapperStruct_T *s)
{
    return Foo(s->f);
}

double Foo(double *x)
{
    return 2.0*x[0];
}

Codegen command:

codegen passStruct -args zeros(1000) Foo.c -report