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c++listiterator
Mihran Hovsepyan
Mihran Hovsepyan

Reputation: 11108

How get next (previous) element in std::list without incrementing (decrementing) iterator?

Say I have an std::list<int> lst and some std::list<int>::iterator it for iterating through the list. And depended to value of the it I want to use it + 1 or it - 1 in my code. Is there some good way to do that like next(), prev() (I couldn't find such things in stl documentation)? Or should I copy the it each time and increment(decrement) the copy?

Upvotes: 60

Views: 56979

Answers (4)

Mikhail Sokolsky
Mikhail Sokolsky

Reputation: 1

if you realize your own list, you can write your own internal class Iterator, where you can easy realize next() and prev() methods throw the reloading of operator--() and operator++()

Upvotes: 0

Stephan Dollberg
Stephan Dollberg

Reputation: 34608

Yes, since C++11 there are the two methods you are looking for called std::prev and std::next. You can find them in the iterator library.

Example from cppreference.com

#include <iostream>
#include <iterator>
#include <list>
 
int main() 
{
    std::list<int> v{ 3, 1, 4 };
 
    auto it = v.begin();
 
    auto nx = std::next(it, 2);
 
    std::cout << *it << ' ' << *nx << '\n';
}

Output:

3 4

Upvotes: 61

Stack Overflow is garbage
Stack Overflow is garbage

Reputation: 248269

Copying and incrementing/decrementing the copy is the only way it can be done.

You can write wrapper functions to hide it (and as mentioned in answers, C++11 has std::prev/std::next which do just that (and Boost defines similar functions). But they are wrappers around this "copy and increment" operation, so you don't have to worry that you're doing it "wrong".

Upvotes: 24

Benjamin Bannier
Benjamin Bannier

Reputation: 58764

A simple precanned solution are prior and next from Boost.utility. They take advantage of operator-- and operator++ but don't require you to create a temporary.

Upvotes: 7

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