Simulink moves class object memory between C-MEX S-Function mdlStart() and mdlOutputs()?

Question

Jonathan Currie 2013-8-25

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https://ww2.mathworks.cn/matlabcentral/answers/85544-simulink-moves-class-object-memory-between-c-mex-s-function-mdlstart-and-mdloutputs

I have a problem where Simulink/Matlab appears to be moving the memory location of a class object between mdlStart() and mdlOuputs() within a C-MEX S Function. I am using mxGetProperty in C, however the pointer returned does not always return my data.

For example:

myclass.prop = [0 1 2];

The way I access this in a C S-Function is as follows (assuming it is the first parameter):

data = mxGetPr(mxGetProperty(ssGetSFcnParam(S, 0),0,"prop"));

Now I expect that the pointer *data should always point to the location of the values within this class object. In mdlStart() where the above line is implemented I can read 0 1 2 correctly. However reading the same pointer (declared globally) from mdlOutputs() all I get is zeros. Using a debugger and looking at the memory location, Matlab.exe is writing over this memory location (which I suspect is during moving this data elsewhere). Typical testing output:

MDLSTART
d[0] 0.000000
d[1] 1.000000
d[2] 2.000000
MDLOUT
d[0] 0.000000
d[1] 0.000000
d[2] 0.000000

Can anyone help me out on this one? It doesn't show in the documentation for mxGetProperty that it is not compatible with S Functions. And as I have 30+ properties and sub-fields to access, I do not want to have to find the pointers every time mdlOutputs() is called!

Test Class Code:

classdef testclass
    properties
        prop
    end
end
>> myclass = testclass(); myclass.prop = [0 1 2];

Test C S-Function (save as testsfun.c)

#define S_FUNCTION_NAME testsfun
#define S_FUNCTION_LEVEL 2
#include <simstruc.h>  
double * data; //global pointer
static void mdlInitializeSizes(SimStruct *S)
{
    ssSetNumSFcnParams(S, 1); 
    ssSetSFcnParamTunable( S, 0, 0 );       
    ssSetNumContStates(S, 0); ssSetNumDiscStates(S, 0);
    if (!ssSetNumInputPorts(S, 0)) return;
    if (!ssSetNumOutputPorts(S, 0)) return;   
    ssSetNumSampleTimes(S, 1);    
    ssSetNumRWork(S, 0); ssSetNumIWork(S, 0);
    ssSetNumPWork(S, 0); ssSetNumModes(S, 0);
    ssSetNumNonsampledZCs(S, 0);
    ssSetSimStateCompliance(S, USE_DEFAULT_SIM_STATE);
    ssSetOptions(S, 0);
}
static void mdlInitializeSampleTimes(SimStruct *S)
{
    ssSetSampleTime(S, 0, 1);
    ssSetOffsetTime(S, 0, 0.0);
    ssSetModelReferenceSampleTimeDefaultInheritance(S);
}
#define MDL_START 
#if defined(MDL_START) 
static void mdlStart(SimStruct *S)
{ 
    data = mxGetPr(mxGetProperty(ssGetSFcnParam(S, 0),0,"prop"));
    ssPrintf("MDLSTART\nd[0] %f\nd[1] %f\nd[2] %f\n",data[0],data[1],data[2]);
}
#endif 
static void mdlOutputs(SimStruct *S, int tid)
{   
    ssPrintf("MDLOUT\nd[0] %f\nd[1] %f\nd[2] %f\n",data[0],data[1],data[2]);
}      
static void mdlTerminate(SimStruct *S)
{
}
#include "simulink.c"

"myclass" is then simply added as the parameter to a Simulink S-Function block which calls testsfun. Problem above is on R2012b 32bit on Win 7 compiled with VS2010.

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Kaustubha Govind 2013-8-26

What about if you create a workspace variable (say p) which holds an instance to "myclass" and enter 'p' as the value of the dialog parameter?

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Simulink moves class object memory between C-MEX S-Function mdlStart() and mdlOutputs()?

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Simulink moves class object memory between C-MEX S-Function mdlStart() and mdlOutputs()?

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