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Preserve Unused Class Properties in Generated C/C++ Code

C/C++ code generated by Embedded Coder® contains unused class properties or structure fields. Removing unused properties or fields helps improve the memory footprint and run time of the code. By default, the code generator removes properties or fields that are unused in the generated C/C++ code.

This feature applies to standalone code generation. You can preserve the unused properties or fields in generated C/C++ code by using the MATLAB® Coder™ app or at the command line.

Preserve Unused Class Properties or Structure Fields by using MATLAB Coder App

To preserve unused properties or fields:

  1. Open the MATLAB Coder app.

  2. On the Generate Code page, click More Settings.

  3. On the Memory tab, select the Preserve unused fields and properties check box.

MATLAB Coder GUI to Preserve Unused Fields and Properties

Preserve Unused Class Properties or Structure Fields at the Command Line

To preserve the unused properties or fields, set the configuration parameter PreserveUnusedStructFields to true and use the configuration object cfg in the codegen command.

cfg = coder.config('lib');
cfg.PreserveUnusedStructFields = true;

Examples

The following examples demonstrate the usage of the PreserveUnusedStructFields configuration option to generate C/C++ code.

Generate C++ Code for MATLAB Classes

This table compares the generated C++ code for myClass, with unused properties removed and with unused properties preserved. In order to preserve the unused class property c, you must assign a value to the property c in the class constructor.

MATLAB Code

Unused Class Properties Removed (default)

Unused Class Properties Preserved

% Entry-point function
function y = myAdd(n)
    %#codegen
    o = myClass(n);
    y = o.a + o.b;
end
classdef myClass
    properties
        a
        b
        c
    end

    methods
        function obj = myClass(x)
            coder.inline('never')
            obj.a = x;
            obj.b = x + 1;
            obj.c = x + 2;
        end
    end
end

Code generation command 

cfg = coder.config('lib');
cfg.TargetLang = "C++";
codegen myAdd -args {5} -config cfg -report

Generated C++ Code

class myClass {
    public:
      void init(double x);
      double a;
      double b;
};

void myClass::init(double x)
{
  a = x;
  b = x + 1.0;
}

Code generation command

cfg = coder.config('lib');
cfg.PreserveUnusedStructFields = true;
cfg.TargetLang = "C++";
codegen myAdd -args {5} -config cfg -report

Generated C++ Code

class myClass {
    public:
        void init(double x);
        double a;
        double b;
        double c;
};

void myClass::init(double x)
{
  a = x;
  b = x + 1.0;
  c = x + 2.0;
}

Generate C Code for MATLAB Structures

This table compares the generated C code for myStruct, with unused fields removed and with unused fields preserved.

MATLAB Code

Unused Structure Fields Removed (default)

Unused Structure Fields Preserved

% Entry-point function
function out = myStruct(n)
    %# codegen
    s.a = [n n n];
    s.b = n+2;
    s.c = n;
    out = myAdd([s s]);
end
function out = myAdd(s)
    coder.inline('never');
    out = s(1).b + s(2).b;
end

Code generation command

cfg = coder.config('lib');
codegen myStruct -args {0} -config cfg -report

Generated C Code

typedef struct {
  double b;
} struct_T;

/*
 * Arguments    : double n
 * Return Type  : double
 */
double myStruct(double n)
{
  struct_T b_s[2];
  struct_T s;
  s.b = n + 2.0;
  b_s[0] = s;
  b_s[1] = s;
  return myAdd(b_s);
}

Code generation command

cfg = coder.config('lib');
cfg.PreserveUnusedStructFields = true;
codegen myStruct -args {0} -config cfg -report

Generated C Code

typedef struct {
  double a[3];
  double b;
  double c;
} struct_T;
 
/* 
 * Arguments    : double n 
 * Return Type  : double 
 */ 
double myStruct(double n)
{
  struct_T b_s[2];
  struct_T s;
  s.a[0] = n;
  s.a[1] = n;
  s.a[2] = n;
  s.b = n + 2.0;
  s.c = n;
  b_s[0] = s;
  b_s[1] = s;
  return myAdd(b_s);
}

Usage Notes

  • When PreserveUnusedStructFields is set to false, the code generator preserves properties or fields of the entry-point function input and output arguments and values passed to coder.ceval.

  • When PreserveUnusedStructFields is set to true, the code generator removes properties or fields whose data types are unknown.

See Also

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