Documentation

coder.ref

Indicate data to pass by reference

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Syntax

coder.ref(arg)

Description

example

coder.ref(arg)indicates thatargis an expression or variable to pass by reference to an external C/C++ function. Usecoder.refinside acoder.cevalcall only. The C/C++ function can read from or write to the variable passed by reference. Use a separatecoder.refconstruct for each argument that you pass by reference to the function.

Examples

Pass Scalar Variable by Reference

Consider the C functionaddonethat returns the value of an input plus one:

double addone(double* p) { return *p + 1; }

The C function defines the input variablepas a pointer to a double.

Pass the input by reference toaddone:

...y = 0; u = 42; y = coder.ceval('addone', coder.ref(u));...

Pass Multiple Arguments by Reference

...u = 1; v = 2; y = coder.ceval('my_fcn', coder.ref(u), coder.ref(v));...

Pass Class Property by Reference

...x = myClass; x.prop = 1; coder.ceval('foo', coder.ref(x.prop));...

Pass a Structure by Reference

To indicate that the structure type is defined in a C header file, usecoder.cstructname.

Suppose that you have the C functionincr_struct. This function reads from and writes to the input argument.

#include "MyStruct.h" void incr_struct(struct MyStruct *my_struct) { my_struct->f1 = my_struct->f1 + 1; my_struct->f2 = my_struct->f2 + 1; }

The C header file,MyStruct.h, defines a structure type namedMyStruct:

#ifndef MYSTRUCT #define MYSTRUCT typedef struct MyStruct { double f1; double f2; } MyStruct; void incr_struct(struct MyStruct *my_struct); #endif

In your MATLAB®function, pass a structure by reference toincr_struct. To indicate that the structure type forshas the nameMyStructthat is defined in the C header fileMyStruct.h, usecoder.cstructname.

functiony = foo%#codegeny = 0; coder.updateBuildInfo('addSourceFiles','incr_struct.c'); s = struct('f1',1,'f2',2); coder.cstructname(s,“MyStruct”,'extern','HeaderFile','MyStruct.h'); coder.ceval('incr_struct', coder.ref(s));

To generate standalone library code, enter:

codegen-config:libfoo-report

Pass Structure Field by Reference

...s = struct('s1', struct('a', [0 1])); coder.ceval('foo', coder.ref(s.s1.a));...

You can also pass an element of an array of structures:

...c = repmat(struct('u',magic(2)),1,10); b = repmat(struct('c',c),3,6); a = struct('b',b); coder.ceval('foo', coder.ref(a.b(3,4).c(2).u));...

Input Arguments

collapse all

Argument to pass by reference to an external C/C++ function. The argument cannot be a class, a System object™, a cell array, or an index into a cell array.

Data Types:single|double|int8|int16|int32|int64|uint8|uint16|uint32|uint64|logical|char|struct
Complex Number Support:Yes

Limitations

  • You cannot pass these data types by reference:

    • Class or System object

    • Cell array or index into a cell array

  • If a property has a get method, a set method, or validators, or is a System object property with certain attributes, then you cannot pass the property by reference to an external function. SeePassing By Reference Not Supported for Some Properties.

Tips

  • Ifargis an array, thencoder.ref(arg)provides the address of the first element of the array. Thecoder.ref(arg)function does not contain information about the size of the array. If the C function must know the number of elements of your data, pass that information as a separate argument. For example:

    coder.ceval('myFun',coder.ref(arg),int32(numel(arg));

  • When you pass a structure by reference to an external C/C++ function, usecoder.cstructnameto provide the name of a C structure type that is defined in a C header file.

  • In MATLAB,coder.refresults in an error. To parameterize your MATLAB code so that it can run in MATLAB and in generated code, usecoder.target.

  • You can usecoder.opaqueto declare variables that you pass to and from an external C/C++ function.

See Also

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Topics

Introduced in R2011a

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