Control Declarations and Definitions of Global Variables in Code Generated from MATLAB Code

This example uses storage classes to control the declarations and definitions of global variables in C/C++ code generated from MATLAB^® code. Using storage classes helps you to interface generated code with external code.

This example requires an Embedded Coder^® license.

Write a function addglobals that adds four global variables. Declare the global variables in the function.

function y = addglobals %#codegen
% Define the global variables.
global u;
global v;
global x;
global z;

% Assign the storage classes.
coder.storageClass('u','ExportedGlobal');
coder.storageClass('v','ImportedExtern');
coder.storageClass('x','ImportedExternPointer');
coder.storageClass('z','ExportedDefine');
y = u + v + x + z;
end

Create a file c:\myfiles\myfile.c that defines and initializes the imported global variables u and v.

#include <stdio.h>

/* Variable definitions for imported variables */ 
double v = 1.0;
double *x = &v;

Create a code configuration object. Configure the code generation parameters to include myfile.c. For output type 'lib', or if you generate source code only, you can generate code without providing this file. Otherwise, you must provide this file.

cfg = coder.config('dll','ecoder', true);
cfg.CustomSource = 'myfile.c';
cfg.CustomInclude = 'c:\myfiles';

Generate the code. This example uses the -globals argument to specify the types and initial values of the global variables u, v, x, and z. Alternatively, you can define global variables in the MATLAB global workspace. For the imported global variables v and x, the code generator uses the initial values only to determine the type.

codegen -config cfg -globals {'u', 1, 'v', 2, 'x', 3, 'z', 4} addglobals -report

From the initial values 1, 2, 3, and 4 codegen determines that u, v, x and z have type double. codegen defines and declares the exported global variables u and z. It generates code that initializes u to 1.0 and z to 4.0. codegen declares the imported global variables v and x. It does not define these variables or generate code that initializes them. myfile.c provides the code that defines and initializes v and x.

To view the code generated for the global variables, open the report. Click the View report link.

View the definition for the exported global z in the Exported data define section in addglobals.h.

/* Definition for custom storage class: ExportedDefine */
#define z                              4.0

View the definition and declaration for the exported global u.

• u is defined in the Variable Definitions section in addglobals.c.

  /* Variable Definitions */
  /* Definition for custom storage class: ExportedGlobal */
  double u;

• u is declared as extern in the Variable Declarations section in addglobals.h.

  /* Variable Declarations */
  /* Declaration for custom storage class: ExportedGlobal */
  extern double u;

• u is initialized in addglobals_initialize.c.

  /* Include Files */
  #include "addglobals_initialize.h"
  #include "addglobals.h"
  #include "addglobals_data.h"
  
  /* Function Definitions */
  
  /*
   * Arguments    : void
   * Return Type  : void
   */
  void addglobals_initialize(void)
  {
    u = 1.0;
    isInitialized_addglobals = true;
  }

View the definition and declaration for the imported external global v and the imported external global pointer x.

v and x are declared as extern in the Variable Declarations section in addglobals_data.h.

/* Variable Declarations */
/* Declaration for custom storage class: ImportedExtern */
extern double v;

/* Declaration for custom storage class: ImportedExternPointer */
extern double *x;