STL列表访问倒数第二个元素

Question

How do I get an iterator to the next-to-last element in a STL list without creating a temporary and modifying the list? Is it possible to just say: --(--mylist.end()) ? Or would this change the end iterator of the list due to the prefix decrement?

Answer 1

Please note that in general, --mylist.end() is not guaranteed to compile for every container.

For example, if you use a std::vector or std::array in release mode, mylist.end() is probably a raw pointer, and you cannot decrement a pointer returned by value from a function.

A generic solution to this problem in C++11 is std::prev(std::prev(mylist.end())) , after checking that the list is long enough, of course. You need to #include <iterator> for this.

Answer 2

You could use std::advance and a reverse_iterator:

SomeContainerType::reverse_iterator it = myList.rbegin();
std::advance(it, 1); // next to last element

This works even if the iterator type in question does not support operator+ .

Answer 3

如果使用reverse_iterator ，则： some_list.rbegin() + 1;