How to create a structure and pass that structure's object as a pointer to a C function in Matlab/Simulink

Hello team,

We need to access a C-function in Matlab. This C function has a double pointer of structure type as an argument. Function updates the pointer with an address of structure field.

% % C code: Function in C
void C_function (structure1** ptr)
{   
    *ptr = &structure1_Obj.info
}

In order to access this function in Matlab (Using matlab function), we need to create the same structure in matlab to pass its object's pointer as an argument to the C function. So eventually, we will get the expected result available in Matlab. Hereby sharing the C code structure architectures for your reference:

% % C code: Structure(Nested) in C
typedef struct structure1
{
    another_Structure info;
}structure1_Obj;

% % C code: Structure in C
typedef struct another_Structure
{
    char name[50];
    int age;
    float height;
}

Please guide us to create the similar structure in Matlab in order to get the expected results in Matlab for further use.

Answer 1

[Hitesh]

Hi Shalaka,

I understand that you want to connect a C function with MATLAB where the function uses a double pointer of a structure type, you typically need to:

1. Use MEX interface (MATLAB Executable C/C++ code).
2. Create equivalent structures in MATLAB using libstruct or struct with loadlibrary/calllib (for shared libraries).
3. Handle the pointer indirection carefully – because MATLAB doesn't directly support double ptr semantics in MATLAB space, you need to handle this pointer manipulation inside a MEX function.

Step 1: Convert your C code into a MEX-compatible C file.

Kindly refer to the following code for creating a MEX wrapper for the C function:

#include "mex.h"
#include <string.h>

// Define your structures
typedef struct {
    char name[50];
    int age;
    float height;
} another_Structure;

typedef struct {
    another_Structure info;
} structure1;

// Global object (example)
structure1 structure1_Obj = {
    .info = {"John", 30, 5.9}
};

// The function to be wrapped
void C_function(structure1** ptr) {
    *ptr = &structure1_Obj;
}
// The MEX gateway function
void mexFunction(int nlhs, mxArray* plhs[], int nrhs, const mxArray* prhs[]) {
    structure1* ptr = NULL;
    C_function(&ptr);  // Get pointer to internal data

    // Create MATLAB structure to return
    const char* field_names[] = {"name", "age", "height"};
    plhs[0] = mxCreateStructMatrix(1, 1, 3, field_names);

    // Fill in fields
    mxSetField(plhs[0], 0, "name", mxCreateString(ptr->info.name));
    mxSetField(plhs[0], 0, "age", mxCreateDoubleScalar(ptr->info.age));
    mxSetField(plhs[0], 0, "height", mxCreateDoubleScalar(ptr->info.height));
}

Step 2: Compile the MEX function in MATLAB using the following command.

mex C_function_mex.c

Make sure the C compiler is set up. If not, run:

mex -setup

Step 3: Call the function in MATLAB

result = C_function_mex();

For more information regarding "mex", kindly refer to the following MATLAB documentation

https://www.mathworks.com/help/matlab/ref/mex.html

[Shalaka]

Hello Hitesh,

Thank you for the quick response. I will try to implement the suggested approach.

I will follow up if necessary. Thanks!

[Shalaka]

Hello Hitesh,

I have implemented the above approach. I can see the required structure fields in Matlab workspace after compilation and execution of the created Mex function. My next query is how to use this MEX file and its output inside a Simulink model?

I need to update certain variables in MATLAB workspace (in a Simulink model) based on this MEX output. Request you to please guide further for the same.