[Scilab-Dev] usage of push_back/front and pop_back/front in scilab API

[Clément David]

Le lundi 09 avril 2018 à 16:07 +0200, Stéphane Mottelet a écrit :
> Le 09/04/2018 à 15:45, Stéphane Mottelet a écrit :
> > Hello,
> > 
> > I have a newbie question about the usage of lists in the new scilab 
> > API. When e.g. you have to construct a list of vectors constructed 
> > from a vector
> > 
> > double* YData
> > 
> > which is updated and to be stored after each update in a list names 
> > pDblYOutList. By writing
> > 
> > pDblYOutList.push_back(pdYData);
> > 
> > at each update, since the address of YData does not change, at the end 
> > every term of the list will contain the same vector (ode bug :-(). I 
> > have some ideas to fix that but how does one proceed *properly* in the 
> > coding style of Scilab API ?
> > 
> > S.
> > 
> > 
> > 
> 
> Supposing that pDblY0 exists, with  the required size, and pDblYOut is a 
> types::Double*, does the following do the trick:
> 
>              pDblYOut = new types::Double(pDblY0->getRows(), 1);
>              pDblYOut->set(pdYData);
>              pDblYOutList.push_back(pDblYOut->get());
> 
> Thanks for hints, comments..
> 
> S.

Hello Stéphane,

As `double* pdYData` is updated you have to copy the data to preserve the history ; you could either
 use Scilab API to store types::Double or plain C++ to store double* :

 auto pDblYOut = new types::Double(pDblY0->getRows(), 1);
 pDblYOut->set(pdYData); // will copy pdYData
 pDblYOutList->getData()->push_back(pDblYOut); // to preserve a pointer to the Scilab datatype with
                                               // types::List* pDblYOutList

OR

 auto temp = new double[pDblY0->getRows()];
 memcpy(temp, pdYData, pDblY0->getRows()*sizeof(double));
 pDblYOutList.push_back(temp); // using std::vector<double*> pDblYOutList

However (especially in ode() case) not that allocating on each loop step can be really slow ; having
all the buffers pre-allocated at first will slightly improve loop caching.

Regards,

--
Clément