about XLL memory management

Rodrigo_ Thanks for reply. I know the static approach and I believe there is a typo in your example, xlbitDLLFree is wrong, which will direct Excel to free (by call back into xlAutoFree12) a static allocated memory. The right one should be.

__declspec(dllexport)
LPXLOPER12 test() {
  static XLOPER12 ret = { xltypeInt, { 10 } };
  return &ret;
}

 What I'm curious is how the xlFree (in xlAutoFree12) know whether an LPXLOPER12 is returned by a thread-safe UDF or by a non thread-safe UDF.

Just few minutes ago, I implemented my free logic as follow

void myxlFree(LPXLOPER12 px) {
  if (px->xltype == xltypeStr) {
    if (px->val.str) {
      delete px->val.str;
      px->val.str = nullptr;
    }
  } else if (px->xltype == xltypeRef ) {
    if(px->val.mref.lpmref) {
      delete px->val.mref.lpmref;
      px->val.mref.lpmref = nullptr;
    }
  } else if (px->xltype == xltypeMulti) {
    if (px->val.array.lparray) {
      auto count = px->val.array.rows*px->val.array.columns;
      for(unsigned i=0; i < count; i++) {
        myxlFree(&px->val.array.lparray[i]);
      }
      delete px->val.array.lparray;
      px->val.array.lparray = nullptr;
    }
  }
}

and replace following line

__declspec(dllexport)
void WINAPI xlAutoFree12(LPXLOPER12 pxFree) {
  Excel12(xlFree,nullptr,1,pxFree);
  delete pxFree;
}

 with

__declspec(dllexport)
void WINAPI xlAutoFree12(LPXLOPER12 pxFree) {
  myxlFree(pxFree);
  delete pxFree;
}

test just works so far. But I'm not sure if there are potential issues.