eml.rref - Pass argument by reference as read-only input

Syntax

[y =] eml.ceval('function_name', eml.rref(argI), ... u_n)

Arguments

argI: Variable passed by reference as a read-only input to the external C/C++ function called in eml.ceval.

Description

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

Caution Embedded MATLAB assumes that a variable passed by eml.rref is read-only and optimizes the code accordingly. Consequently, the C/C++ function must not write to the variable or results can be unpredictable.

Only use eml.rref in Embedded MATLAB code that you have compiled with emlmex or emlc. eml.rref generates an error in uncompiled MATLAB 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 foo, passing u by reference as a read-only 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('foo', eml.rref(u));

The corresponding C function prototype looks like this:

real_T foo(real_T *a)

In this example, Embedded MATLAB 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/C++.

eml.rref - Pass argument by reference as read-only input

Syntax

Arguments

Description

Example

See Also

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