This example shows how to control whether structure arguments to generated entry-point functions are passed by reference or by value.
Passing by reference uses a pointer to access the structure arguments. If the function writes to an element of the input structure, it overwrites the input value. Passing by value makes a copy of the input or output structure argument. To reduce memory usage and execution time, use pass by reference.
If a structure argument is both an input and output, the generated entry-point function passes the argument by reference. Generated MEX functions pass structure arguments by reference. For MEX function output, you cannot specify that you want to pass structure arguments by value.
To open the Generate dialog box, on the Generate Code page, click the Generate arrow.
Set the Build type to one of the following:
Source Code
Static Library
Dynamic Library
Executable
Click More Settings.
On the All Settings tab, set the Pass structures by reference to entry-point functions option to:
Yes, for pass by reference (default)
No, for pass by value
Create a code configuration object for a static library, a dynamic library, or an executable program. For example, create a code configuration object for a static library.
cfg = coder.config('lib');Set the PassStructByReference property to:
true, for pass by reference (default)
false, for pass by value
For example:
cfg.PassStructByReference = true;
Write the MATLAB function my_struct_in that has an input structure argument.
function y = my_struct_in(s) %#codegen y = s.f;
Define a structure variable mystruct in the MATLAB® workspace.
mystruct = struct('f', 1:4);
Create a code generation configuration object for a C static library.
cfg = coder.config('lib');
Specify that you want to pass structure arguments by reference.
cfg.PassStructByReference = true;
Generate code. Specify that the input argument has the type of the variable mystruct.
codegen -config cfg -args {mystruct} my_struct_in
View the generated C code.
type codegen/lib/my_struct_in/my_struct_in.c
/*
* File: my_struct_in.c
*
* MATLAB Coder version : 5.1
* C/C++ source code generated on : 30-Jul-2020 01:27:12
*/
/* Include Files */
#include "my_struct_in.h"
#include "my_struct_in_types.h"
/* Function Definitions */
/*
* Arguments : const struct0_T *s
* double y[4]
* Return Type : void
*/
void my_struct_in(const struct0_T *s, double y[4])
{
y[0] = s->f[0];
y[1] = s->f[1];
y[2] = s->f[2];
y[3] = s->f[3];
}
/*
* File trailer for my_struct_in.c
*
* [EOF]
*/
The generated function signature for my_struct_in is
void my_struct_in(const struct0_T *s, double y[4])
my_struct_in passes the input structure s by reference.
Specify that you want to pass structure arguments by value.
cfg.PassStructByReference = false;
Generate code. Specify that the input argument has the type of the variable mystruct.
codegen -config cfg -args {mystruct} my_struct_in
View the generated C code.
type codegen/lib/my_struct_in/my_struct_in.c
/*
* File: my_struct_in.c
*
* MATLAB Coder version : 5.1
* C/C++ source code generated on : 30-Jul-2020 01:27:13
*/
/* Include Files */
#include "my_struct_in.h"
#include "my_struct_in_types.h"
/* Function Definitions */
/*
* Arguments : const struct0_T s
* double y[4]
* Return Type : void
*/
void my_struct_in(const struct0_T s, double y[4])
{
y[0] = s.f[0];
y[1] = s.f[1];
y[2] = s.f[2];
y[3] = s.f[3];
}
/*
* File trailer for my_struct_in.c
*
* [EOF]
*/
The generated function signature for my_struct_in is
void my_struct_in(const struct0_T s, double y[4]
my_struct_in passes the input structure s by value.
Write the MATLAB function my_struct_out that has an output structure argument.
function s = my_struct_out(x) %#codegen s.f = x;
Define a variable a in the MATLAB® workspace.
a = 1:4;
Create a code generation configuration object for a C static library.
cfg = coder.config('lib');
Specify that you want to pass structure arguments by reference.
cfg.PassStructByReference = true;
Generate code. Specify that the input argument has the type of the variable a.
codegen -config cfg -args {a} my_struct_out
View the generated C code.
type codegen/lib/my_struct_out/my_struct_out.c
/*
* File: my_struct_out.c
*
* MATLAB Coder version : 5.1
* C/C++ source code generated on : 30-Jul-2020 01:27:15
*/
/* Include Files */
#include "my_struct_out.h"
#include "my_struct_out_types.h"
/* Function Definitions */
/*
* Arguments : const double x[4]
* struct0_T *s
* Return Type : void
*/
void my_struct_out(const double x[4], struct0_T *s)
{
s->f[0] = x[0];
s->f[1] = x[1];
s->f[2] = x[2];
s->f[3] = x[3];
}
/*
* File trailer for my_struct_out.c
*
* [EOF]
*/
The generated function signature for my_struct_out is
void my_struct_out(const double x[4], struct0_T *s)
my_struct_out passes the output structure s by reference.
Specify that you want to pass structure arguments by value.
cfg.PassStructByReference = false;
Generate code. Specify that the input argument has the type of the variable a.
codegen -config cfg -args {a} my_struct_out
View the generated C code.
type codegen/lib/my_struct_out/my_struct_out.c
/*
* File: my_struct_out.c
*
* MATLAB Coder version : 5.1
* C/C++ source code generated on : 30-Jul-2020 01:27:17
*/
/* Include Files */
#include "my_struct_out.h"
#include "my_struct_out_types.h"
/* Function Definitions */
/*
* Arguments : const double x[4]
* Return Type : struct0_T
*/
struct0_T my_struct_out(const double x[4])
{
struct0_T s;
s.f[0] = x[0];
s.f[1] = x[1];
s.f[2] = x[2];
s.f[3] = x[3];
return s;
}
/*
* File trailer for my_struct_out.c
*
* [EOF]
*/
The generated function signature for my_struct_out is
struct0_T my_struct_out(const double x[4])
my_struct_out returns an output structure.
When an argument is both an input and an output, the generated C function passes the argument by reference even when PassStructByReference is false.
Write the MATLAB function my_struct_inout that has a structure argument that is both an input argument and an output argument.
function [y,s] = my_struct_inout(x,s) %#codegen y = x + sum(s.f);
Define the variable a and structure variable mystruct in the MATLAB® workspace.
a = 1:4;
mystruct = struct('f',a);
Create a code generation configuration object for a C static library.
cfg = coder.config('lib');
Specify that you want to pass structure arguments by value.
cfg.PassStructByReference = false;
Generate code. Specify that the first input has the type of a and the second input has the type of mystruct.
codegen -config cfg -args {a, mystruct} my_struct_inout
View the generated C code.
type codegen/lib/my_struct_inout/my_struct_inout.c
/*
* File: my_struct_inout.c
*
* MATLAB Coder version : 5.1
* C/C++ source code generated on : 30-Jul-2020 01:27:18
*/
/* Include Files */
#include "my_struct_inout.h"
#include "my_struct_inout_types.h"
/* Function Definitions */
/*
* Arguments : const double x[4]
* const struct0_T *s
* double y[4]
* Return Type : void
*/
void my_struct_inout(const double x[4], const struct0_T *s, double y[4])
{
double b_y;
b_y = ((s->f[0] + s->f[1]) + s->f[2]) + s->f[3];
y[0] = x[0] + b_y;
y[1] = x[1] + b_y;
y[2] = x[2] + b_y;
y[3] = x[3] + b_y;
}
/*
* File trailer for my_struct_inout.c
*
* [EOF]
*/
The generated function signature for my_struct_inout is
void my_struct_inout(const double x[4], const struct0_T *s, double y[4])
my_struct_inout passes the structure s by reference even though PassStructByReference is false.