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Matlab/Simulink: Minimal empty template S-function

You can use this minimal, empty s-function as a template for getting started with your own S-function.

This minimal example also includes a template mdlStart().

Remember that if you rename the file, you also need to update the S_FUNCTION_NAME #define accordingly.

#define S_FUNCTION_NAME  nothing_sfunction
#define S_FUNCTION_LEVEL 2

#include "simstruc.h"

// Function: mdlInitializeSizes ===============================================
// Abstract:
//   Setup sizes of the various vectors.
static void mdlInitializeSizes(SimStruct *S)
{
    // Add ssSetNumInputPorts() etc here
}

#define MDL_START
static void mdlStart(SimStruct *S)
{
    // Optionally, perform initialization tasks here
    // If not needed, you can remove this function and #define MDL_START entirely.
}

// 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 nothing_sfunction.cpp CXXFLAGS="-std=gnu++17 -fPIC"

Using -std=gnu++17 or newer is recommended, but not required.