Why matlab crashes when I am trying to change cmex s-function parameter?

When the model is simulated, i can change every parameter. When I am trying to change any parameter before starting simulation, i get Segmentation violation error. When I put into s-function parameters not number, but some letters it is accepted, but Segmentation violation error occurs during creating mask for a block.

Should I change something in my S-function?

in mdlInitializeSizes(SimStruct *S)

    ssSetNumSFcnParams(S, 3);

    ssSetSFcnParamTunable(S,0,SS_PRM_TUNABLE);
    ssSetSFcnParamTunable(S,1,SS_PRM_TUNABLE);
    ssSetSFcnParamTunable(S,2,SS_PRM_TUNABLE);
    if (ssGetNumSFcnParams(S) != ssGetSFcnParamsCount(S)) 
   {return; }

in mdlOutput

    int_T first=(int_T)*mxGetPr(ssGetSFcnParam(S,0));
    int_T second=(int_T)*mxGetPr(ssGetSFcnParam(S,1));
    int_T third=(int_T)*mxGetPr(ssGetSFcnParam(S,2));