Changing elements of lists

[wiczerd]

I am reading lines from a CSV and don't know what size it'll be, so I place read lines into a list of a structure "obs". Then I want to iterate through this list, put it into another list and then modify contents of the original list so that I can print that later. I am, however, not sure if I'm actually modifying the original.

using namespace std;
struct obs{
	int date;
	int p;
	int attr_price;
	int q;
	double bcode;
	double uniq_store_id;
};

int main(){
	string line;
	ifstream fdata("jumboa_corrected.csv");
        obs last_obs;
        getline(fdata,line);
	int scanned = sscanf(line.c_str(),"%i,%i,%i, %lf, %lf",&last_obs.q,&last_obs.date,&last_obs.p,
		&last_obs.bcode,&last_obs.uniq_store_id);
	list<obs> this_series(1,last_obs);
	obs this_obs;
	while(getline(fdata,line)){
		++gi;
		sscanf(line.c_str(),"%i, %i,%i, %lf, %lf",&this_obs.q,&this_obs.date,&this_obs.p,&this_obs.bcode,&this_obs.uniq_store_id);
		this_series.push_front(this_obs);

... stuff that fills in a bunch of this_obs into the list
	if(condition to start unloading){
		list<obs*> qtr_ser_obs;
		for (list<obs>::reverse_iterator it=this_series.rbegin() ; it != this_series.rend(); ++it )
		{
			qtr_ser_obs.push_front(&*it);
                         for (list<obs*>::reverse_iterator qtr_obs_it =qtr_ser_obs.rbegin(); qtr_obs_it !=qtr_ser_obs.rend();qtr_obs_it++){
				(*qtr_obs_it)->attr_price= computed_attr_price;
                        }
                  }
}

In this last line, what am I modifying?
Any help would be greatly appreciated. I guess I'm really not sure what is being placed with the line " qtr_ser_obs.push_front(&*it); "

[kvprajapati]

Welcome wiczerd,

wiczerd said,

I am, however, not sure if I'm actually modifying the original.
...
In this last line, what am I modifying?

Print the list after modification. However, there is no reason to add list item into another list to modify and see; qtr_ser_obs list will add more and more list items and the inner loop is started from the very first element - qtr_ser_obs.rbegin().

list<obs*> qtr_ser_obs;
for (list<obs>::reverse_iterator it=this_series.rbegin() ; it != 
                              this_series.rend(); ++it )
 {
    qtr_ser_obs.push_front(&*it);
    for (list<obs*>::reverse_iterator qtr_obs_it =qtr_ser_obs.rbegin
                 (); qtr_obs_it !=qtr_ser_obs.rend();qtr_obs_it++)
          {
	(*qtr_obs_it)->attr_price= computed_attr_price;
                }
   }

I think it should be:

for (list<obs>::reverse_iterator it=this_series.rbegin() ; it != 
                              this_series.rend(); ++it )
 {
    list<obs*> qtr_ser_obs;
    qtr_ser_obs.push_front(&*it);
    for (list<obs*>::reverse_iterator qtr_obs_it =qtr_ser_obs.rbegin
                 (); qtr_obs_it !=qtr_ser_obs.rend();qtr_obs_it++)
          {
	(*qtr_obs_it)->attr_price= computed_attr_price;
                }
   }

[wiczerd]

Thanks very much. The suggestion to print my list was very helpful, and it seems that I am modifying the original objects.
My syntax got a bit screwed up because I tried cutting and pasting from a much larger program, but your catch was good.
The reason I am moving things from one list to the other is because I need to do calculations on a moving window of the data in the larger list. So I was reading everything into the larger list, and then putting snippets into the smaller one and hoping to modify the initial obs by referencing them through the subset list.