How to insert in a std::list using iterator?

Question

How to insert something in a list using its iterator? for example, I have a list of objects myobj where myobj contains another list<int>.

class myobj {
    //other data goes here
    list<int> l;
};
list <myobj> x;

Suppose I want to call the insert() function for the list in the nth element of x, I'll do something like

list<myobj>::iterator itr = x.begin();
std::advance(itr,n);
itr->insert(n); //It gives a compilation error.

I tried to learn insert_iterator but most of the examples I got were used with copy() function but here I want to call the insert() function of the list inside myobj.

The compiler should be choking on your use of a `list` iterator on a `list` list. — Mikel F, Dec 24 '16 at 17:41

Mikel F · Accepted Answer · 2016-12-24T18:05:40.390

0

There is no operator +=() defined for std::list iterators. To advance your iterator use std::advance.

http://en.cppreference.com/w/cpp/iterator/advance

auto iter = x.begin();
std::advance(iter,n);

Keep in mind that you want to be certain your list is large enough for the iteration you are trying to perform.

To access the contents:

iter->l.insert(n);

When using an iterator, the '.' operator returns methods held by the iterator. If you dereference the iterator, (*iter). or use the operator ->() You should get access to the methods held by the object in your list.

edited Dec 24 '16 at 18:05

answered Dec 24 '16 at 17:27

Mikel F

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Thanks for the help but that's not what I am trying to do. I have a list `list = x` and I don't want to insert into `x` but into the list contained at `nth` element of `x`. – Yousuf Khan Dec 24 '16 at 17:32
@Anon Saw that after I reread your post. Edited to address that. – Mikel F Dec 24 '16 at 17:35
Got it. Thanks alot :) – Yousuf Khan Dec 24 '16 at 18:03
1

There is `operator+=` for *some* iterators---only those of the random access iterator category, which `std::list::iterator` is not, for obvious reasons. – Brian Bi Dec 24 '16 at 18:04
@Brian Thank you sir. Edited to reflect that. – Mikel F Dec 24 '16 at 18:06

score 0 · Answer 2 · answered Dec 24 '16 at 19:25

0

The call you want is l.insert(iter, value);

That inserts the object named value into the list l at the position pointed to by iter.

answered Dec 24 '16 at 19:25

Marshall Clow

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How to insert in a std::list using iterator?

2 Answers2