eml.ref - Pass argument by reference as read input or write output

Syntax

[y =] eml.ceval('function_name', eml.ref(arg), ... u_n)

Arguments

arg

Variable passed by reference as an input or an output to the external C function called in eml.ceval.

Description

[y =] eml.ceval('function_name', eml.ref(arg), ... u_n) passes the variable arg by reference as an input or an output to the external C function called in eml.ceval. You add eml.ref inside eml.ceval as an argument to function_name. The argument list can contain multiple eml.ref constructs. Add a separate eml.ref construct for each argument that you want to pass by reference to function_name.

Only use eml.ref in Embedded MATLAB code that you have compiled with emlmex or emlc. eml.ref generates an error in uncompiled M-code.

Example

In the following example, an Embedded MATLAB function fcn has a single input u and a single output y. fcn calls a C function my_fcn, passing u by reference as an input. The value of output y is passed to fcn by the C function through its return statement.

Here is the Embedded MATLAB function code:

function y = fcn(u)

y = 0; %Constrain return type to double
y = eml.ceval('my_fcn', eml.ref(u));

The corresponding C function prototype looks like this:

real_T my_fcn(real_T *a)

In this example, the Embedded MATLAB subset infers the type of the input u from its definition in the parent model.

The C function prototype defines the input as a pointer because it is passed by reference.

Embedded MATLAB cannot infer the type of the output y, so you must set it explicitly—in this case to a constant value 0 whose type defaults to double, matching the C type real_T. For a list of type mappings, see Mapping MATLAB Types to C.

See Also

eml.ceval, eml.rref, eml.wref

eml.opaque

eml.rref

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