problem with list iterator

[blueeyedlion]

I'm comparing all elements in a std::list for object collision, my problem arises when I try to do this:

std::list<Asteroid>::iterator otherObject = currentObject + 1
currentObject is also an iterator.

This comes up with an error saying that there is no match for the + operator.
What can I do to get around this?

[Cubbi]

List iterators are not random access iterators.

You can use std::next(), as in
std::list<Asteroid>::iterator otherObject = std::next(currentObject);

or, if you have an older compiler, increment

std::list<Asteroid>::iterator otherObject = currentObject;
++otherObject;

But is there a reason you're using a list rather than, say, a vector? Do you actually use list::splice()?

[blueeyedlion]

I need to use a list because at one point there is a list of objects that need to be deleted from the list, and the iterators need to be undisturbed.

Also, can you point me to a reference page for std::next ()?

[Cubbi]

Ok, that is a good reason too. next is http://en.cppreference.com/w/cpp/iterator/next

[blueeyedlion]

Problem:

when I use std::next, an error comes up saying that it is not a member of std.

I did #include <iterator>

[Moschops]

Did you use it with correct parameters?

[andywestken]

std::next() is C++11, the language formerly known as C++0x, not regular C++

From http://stackoverflow.com/questions/3673684/peek-the-next-element-in-stl-container

C++0x adds a handy utility function, std::next, that copies an iterator, advances it, and returns the advanced iterator. You can easily write your own std::next implementation:

#include <iterator>

template <typename ForwardIt>
ForwardIt next(ForwardIt it, 
               typename std::iterator_traits<ForwardIt>::difference_type n = 1)
{
    std::advance(it, n);
    return it;
}

Andy

PS I think people should flag C++11 specific code up until it's in wide(-ish) spread usage!

[blueeyedlion]

ah yes, I've been meaning to upgrade to that for the auto feature.

I have g++ through mingw, how can I upgrade?

[andywestken]

I'm mainly a VC++ user, but I have heard that with Gnu (g++ is gnu?) you just have to enable C++11 with a compiler flag. If you're up to date enough, I guess (GCC 4.3 and later).

http://gcc.gnu.org/projects/cxx0x.html

--std=c++0x

[blueeyedlion]

that worked, thanks!

[bluecoder]

Hi ,
The code i tried is not working on window .
giving the error as next undefined .

please advice . Thanks in advance

//

#include "stdafx.h"
#include <iostream>
#include <iterator>
#include <vector>


using namespace std; 




int _tmain(int argc, _TCHAR* argv[])
{
	int array1[] = { 1 , 2 ,3 ,4 ,5,6 ,7 };
	vector<int> v( array1 , array1 + sizeof(array1) / sizeof( int ) );
	vector<int>::iterator it ; 
	//auto it;
	it = v.begin();
	vector<int>::iterator nx	= next(it , 3);
	cout<<"\n Begning = "<<*it<<"\t next after 3 position = "<<*nx;
	return 0;
}

[Moschops]

Get a compiler that understands C++ 11 :)

[bluecoder]

thanks Moschops..