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Minimal Simulink S-function which takes a string as parameter

This S-function is the minimal implementation which takes a string as an S-function parameter. It is based on Matlab/Simulink: Minimal empty template S-function

Important: You need to pass the S-function parameter in single quotes ('), passing them in double quotes does NOT work and will lead to the S-function receiving an empty string parameter.

S Function parameter dialog with string parameter

#define S_FUNCTION_NAME  string_param_sfunc
#define S_FUNCTION_LEVEL 2

#include "simstruc.h"

// Function: mdlInitializeSizes ===============================================
// Abstract:
//   Setup sizes of the various vectors.
static void mdlInitializeSizes(SimStruct *S)
{
    // One parameter: String
    ssSetNumSFcnParams(S, 1);
}

#define MDL_START
static void mdlStart(SimStruct *S)
{
    // Extract string parameter
    const mxArray *param = ssGetSFcnParam(S, 0);
    if(!mxIsChar(param)) {
        ssSetErrorStatus(S, "Parameter is not a string!");
        return;
    }
    const char* pCharArray = mxArrayToString(param);

    printf("Extracted string parameter '%s'\n", pCharArray);

    mxFree((void*)pCharArray);
}

// Function: mdlInitializeSampleTimes =========================================
// Abstract:
//    Initialize the sample times to be 1ms (1kHz)
static void mdlInitializeSampleTimes(SimStruct *S)
{
    // For an example what to add here, see https://techoverflow.net/2024/10/20/matlab-level-2-s-function-example-sine-wave-continous-output/
}

// Function: mdlOutputs =======================================================
// Abstract:
//      Calculate the sine wave output based on the simulation time.
static void mdlOutputs(SimStruct *S, int_T tid)
{
    // For an example what to add here, see https://techoverflow.net/2024/10/20/matlab-level-2-s-function-example-sine-wave-continous-output/
}

// Function: mdlTerminate =====================================================
// Abstract:
//    This function is called at the end of simulation for cleanup.
static void mdlTerminate(SimStruct *S)
{
    // No cleanup required for this example
}

// Required S-function trailer
#ifdef MATLAB_MEX_FILE
#include "simulink.c"   // MEX-file interface mechanism
#else
#include "cg_sfun.h"    // Code generation interface
#endif

Compile using

mex -g string_param_sfunc.cpp CXXFLAGS="-std=gnu++17 -fPIC"