Two questions involving STD Lists

[IonBlade]

In my game, i use a list for my entities, among other things.

my first question is... is it possible to declare an extern list? i want to be able to access my list of entities from anywhere in my code (including other source files). example...

in main.cpp....

list <CBaseEntity *> entities;
blalbbllah
blahblah
blah

in say, weapons.h....

extern ????????? entities;

and now in weapons.cpp.....

object_thingy *object = new Object();
entities.push_back(object);

and finally my second question, how would i go about getting the total number of elements in a list? for example, i want to check if a list contains over 200 elements, and then delete everything past 200 to save on memory.

[XSquared]

You mean STL lists, right?

1) No clue.
2) Use the size( ) method to get the size, then you can use an iterator to get to the 200th element, then use the erase( ) method.

[jlou]

Originally posted by IonBlade
and finally my second question, how would i go about getting the total number of elements in a list? for example, i want to check if a list contains over 200 elements, and then delete everything past 200 to save on memory.

I'm not sure a list is the best option if you need to iterate to find the 200th element. You'll probably want to access that 200th element randomly - meaning you won't need to loop through all 199 elements before it. I don't know of any efficient way to lop off all elements after 200 in a list container without navigating your way to the 200th element first.

A better container might be a deque or a vector. You can get an iterator to the 200th element simply by calling at(200) (technically that would be the 201st element). You can then use that iterator with erase/remove. You can push_back on to a deque or vector just like a list, but you cannot insert an element into the middle as efficiently as you can with a list. However, if you don't do any inserts, only push_back, then deque or vector is for you. Or if you use push_front, then deque (not vector) might be better.

As far as your first question, I don't know any reason why it wouldn't be possible. Are you having problems with it?

[IonBlade]

yeah lol, STL. STD? god now i feel like an idiot damn abbreviations, SDL, STL, STD, same thing..

As far as your first question, I don't know any reason why it wouldn't be possible. Are you having problems with it?

i'm just not sure of the syntax. and yes i have tried and i got errors.

extern list entities;
extern list *entities;
extern list<CBaseEntity *> entities;

i have tried all those, and get "syntax error before ';' ".

sorry if i sound noobish, but i'm just starting with the STL. and that list of 200 elements is what i'm using to keep a console/message log, it's just a list of char strings, and i want to delete past messages when about 200 exist.

[grib]

extern works fine with stl, the only problems you might find is forgetting to actually declare it somewhere, or more than one place. Both don't show up utill linkage though. I would suggest

#ifndef CONLIST_H
#define CONLINST_H
#include<deque>
#include<string>
typedef std::deque<std::string> conlist_t;
extern conlist_t entities;
#endif

//in one, and only one cpp file
#include"conlist.h"
conlist_t entities;

and just let entities expand to it's little hearts desire. If 200 lines is too much to deal with from a user standpoint then wrap deque around your own class that has a limit that when you add a line and size() > limit it pop_front()s when it push_back()s the new line.