std::list - access at index?

[Gernot Frisch]

Hi,

how can I access the nth element in a std::list?? Or should I use a
deque/queue instead?

Thank you,
--
-Gernot
int main(int argc, char** argv) {printf
("%silto%c%cf%cgl%ssic%ccom%c", "ma", 58, 'g', 64, "ba", 46, 10);}

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[Marcin Kalicinski]

Hi,

You cannot access list element by index. If you want to do it you have to
use vector or deque. You can only access list elements via iterators, or by
front() and back() members.

Cheers,
Marcin

 

[John Harrison]

Hi,

how can I access the nth element in a std::list?? Or should I use a
deque/queue instead?

You can't do it efficiently.

#include <iterator>

list<int> x;
....
list<int>::iterator i = x.begin();
std::advance(i, n);
// now i points to the nth member of the list (counting from zero)

Wrap this up in a function and you'll get the same functionality as the MFC
classes you are porting. I would imagine that MFC was doing something
equally inefficient behind the scenes.

john

 

[Gernot Frisch]

You can't do it efficiently.

Yes, I know.

#include <iterator>

list<int> x;
...
list<int>::iterator i = x.begin();
std::advance(i, n);
// now i points to the nth member of the list (counting from zero)

Ah. "std::advance", that was what I was looking for. I need to use
list, so the pointers to my elements stay after insertion of new
elements, thus I can't use vector. I don't care about speed, since I
only have one function where I have to find an element at given index,
and it's not a very important one.

Thank you very much,
Gernot