Does C++ list.erase(it, it) erase something? Where to find good references?

Question

I mean in situation when the iterators point on same element.

On http://www.cplusplus.com/reference/stl/list/erase/ say "Removes from the list container either a single element (position) or a range of elements ([first,last))." and "first, last Iterators specifying a range within the list container to be removed: [first,last). i.e., the range includes all the elements between first and last, including the element pointed by first but not the one pointed by last."

I totally don't know if I do everything wrong but for every part of my code I don't find needed information anywhere and when I want to test it by myself, I end in a situation, when I don't know what happened and after asking here and arguing for long hours I find something like "undefined behavior". So can someone help me faster, what is it now?

And I want to be better programmer and find out better source than cplusplus.com and cppreference.com, because they both suck, is there something better? I am getting crazier every day with this C++ (but I still think it's much better for speedy huge programs than Java or C), please help.

Why don't you just try it and see? Create a list, get an iterator to the middle, call erase(), and see what the contents are afterwards. — riwalk, Sep 20 '12 at 20:33
@Lukas How about referring to the standard if you want reference ? — Mahesh, Sep 20 '12 at 20:34
Why not fill the list, print it, call erase(it, it) and print the list again? — TeaOverflow, Sep 20 '12 at 20:35
@Stargazer712 Because I won't be sure if it's not an undefined behavior like million times before or if it's done OK. — Lukas Salich, Sep 20 '12 at 20:40
Just FYI, when you are a little more experienced, cplusplus.com is a godsend. I think you also need to look into iterators and general data structures more as I have a feeling that you're misunderstanding something. — Ray Dey, Sep 20 '12 at 20:42
@Evgeni Cplusplus.com and cppreference.com always have only basics of the problem I try to solve, but I need more information. — Lukas Salich, Sep 20 '12 at 20:43
[Do not use cplusplus.com, use cppreference.com](http://jcatki.no-ip.org/fncpp/cplusplus.com). — Griwes, Sep 20 '12 at 20:44

score 9 · Accepted Answer · answered Sep 20 '12 at 20:46

The Standard's own definition of ranges (24.2.1p7, emphasis mine):

Most of the library’s algorithmic templates that operate on data structures have interfaces that use ranges. A range is a pair of iterators that designate the beginning and end of the computation. A range [i,i) is an empty range; in general, a range [i,j) refers to the elements in the data structure starting with the element pointed to by i and up to but not including the element pointed to by j.

So assuming it is a valid iterator in or past-the-end of lst, the call lst.erase(it,it) erases an empty set of elements from lst. That is, it does nothing.

I hope it's true and where can I find those "The Standard's own definition"s? — Lukas Salich, Sep 20 '12 at 20:53

score 2 · Answer 2 · answered Sep 20 '12 at 20:42

2

I think to best answer your question you should think about how iterators work and why everything is passed in as [first, last) and not something else.

There are two core rules about iterators that you need to keep in mind. You can always increment one (that is to say, first++) and two iterators that point to the same element will always be equal. Knowing this you can loop over ANY range of iterators with the logic:

for(; first != last; first++)
{
}

So, if first and last are equal, nothing will happen. So if you call list.erase(it, it) nothing will be erased.

To put it in a more general form. Any range in STL where first == last is effectively empty.

answered Sep 20 '12 at 20:42

Fox Cutter

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OK, I thought it also, but how can you be so sure? Where is it written? You went through the list functions? – Lukas Salich Sep 20 '12 at 20:46
@LukasSalich No matter what the standard says, the best way to be sure is to write code, compile it, and run it. – Code-Apprentice Sep 20 '12 at 20:57
1

@LukasSalich You can't be sure that your compiler implements the standard, either. – Code-Apprentice Sep 20 '12 at 21:08
@Code-Guru And that's the problem :( – Lukas Salich Sep 20 '12 at 21:13
@LukasSalich Perhaps you need to clarify the question. Are you asking what *should* happen or what actually *does* happen? From the title, I believe you are asking the former. Perhaps an edit will help clarify that. – Code-Apprentice Sep 20 '12 at 21:18

Does C++ list.erase(it, it) erase something? Where to find good references?

2 Answers2