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How to convert a C structure (returned by dll) to MATLAB structure?

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Jack Liber
Jack Liber 2021-12-10
编辑： Sameer 2024-2-19
Hi,
I have a dll that can read A2L files to a C structure that I would then link to manipulate in MATLAB so that I can use information from Simulink to make changes.
Is there a way for MATLAB to read the C structure as a MATLAB structure?
I have a header file that describes the structure and functions.
Thanks
  1 个评论
Rik
Rik 2021-12-10
You could have a look on this GitHub page, which contains C code to deal with Matlab structs. I don't know what the 'correct' way would be to deal with the conversion.

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回答（1 个）

Sameer
Sameer 2024-2-19
编辑：Sameer 2024-2-19
Hi Jack,
I understand that you're looking to integrate a C structure from a DLL into MATLAB and interact with it as a MATLAB structure. To achieve this, you can write custom code using a MATLAB Executable (MEX) file. MEX files serve as a bridge, allowing you to execute C, C++, or Fortran code within MATLAB's environment.
Let's consider a scenario where you have a C structure that represents a point in 3D space, and you have a DLL that provides this structure. The structure in C might look like this:
// C structure for a 3D point
typedef struct
{
double x;
double y;
double z;
} Point3D;
Assuming you have a function in your DLL that returns this Point3D structure, and you want to convert it into a MATLAB structure. Here's how you can write a MEX function to do this:
Step 1: Include Necessary Headers
#include "mex.h"
// Include the header that defines Point3D and the function to get a point
#include "your_header.h"
Step 2: Define the MEX Function The entry point of a MEX file is the mexFunction. It has a specific signature that MATLAB recognizes:
void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])
{
// code
}
Step 3: Get the Point3D Structure from the DLL Inside mexFunction, call the DLL function that returns the Point3D structure:
// Assume getPointFromDLL is a function in your DLL that returns a Point3D
Point3D point = getPointFromDLL();
Step 4: Create MATLAB Structure Define the field names and create the MATLAB structure that corresponds to the Point3D C structure:
// Define field names
const char *fieldNames[] = {"x", "y", "z"};
int numberOfFields = 3; // We have three fields: x, y, z
// Create a 1x1 MATLAB structure with these fields
plhs[0] = mxCreateStructMatrix(1, 1, numberOfFields, fieldNames);
Step 5: Populate the MATLAB Structure Convert the C structure fields into MATLAB data and populate the MATLAB structure:
// Populate the MATLAB structure with data from the Point3D structure
mxSetField(plhs[0], 0, "x", mxCreateDoubleScalar(point.x));
mxSetField(plhs[0], 0, "y", mxCreateDoubleScalar(point.y));
mxSetField(plhs[0], 0, "z", mxCreateDoubleScalar(point.z));
Put it all together to form the complete MEX function:
#include "mex.h"
#include "your_header.h"
// Example C structure for a 3D point
typedef struct
{
double x;
double y;
double z;
} Point3D;
// Function to interface with the DLL (placeholder)
Point3D getPointFromDLL()
{
Point3D point;
// Assume your DLL populates this structure
point.x = 1.0;
point.y = 2.0;
point.z = 3.0;
return point;
}
// MEX function to convert Point3D to MATLAB structure
void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])
{
// Get the Point3D structure from the DLL
Point3D point = getPointFromDLL();
// Define field names
const char *fieldNames[] = {"x", "y", "z"};
int numberOfFields = 3;
// Create a 1x1 MATLAB structure with these fields
plhs[0] = mxCreateStructMatrix(1, 1, numberOfFields, fieldNames);
// Populate the MATLAB structure with data from the Point3D structure
mxSetField(plhs[0], 0, "x", mxCreateDoubleScalar(point.x));
mxSetField(plhs[0], 0, "y", mxCreateDoubleScalar(point.y));
mxSetField(plhs[0], 0, "z", mxCreateDoubleScalar(point.z));
}
Step 6: Compile the MEX File In MATLAB:
mex your_mex_file.c
Step 7: Once compiled, you can call the MEX file from MATLAB like any other function:
pointStruct = your_mex_file;
%This will return a MATLAB structure pointStruct with fields x, y, and z.
For additional information, please refer to the links below:
www.mathworks.com/help/releases/R2019b/matlab/ref/mex.html
www.mathworks.com/help/releases/R2019b/matlab/apiref/mxcreatestructmatrix.html
www.mathworks.com/help/releases/R2019b/matlab/apiref/mxsetfield.html
www.mathworks.com/help/releases/R2019b/matlab/apiref/mxcreatedoublescalar.html

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