算法forward_list排序了吗？

Question

I have some difficulties in C++11. I would like to create function isSorted which return true if my std::forward_list is sorted, and false if not.

I have imagined code like this:

template<class T>
bool estTriee(forward_list<T>& list) {
        typename forward_list<T>::iterator it;
        it = list.begin();

        while(it != list.end() &&  *it <= *next(it, 1)) {
            it++;
        }

        return it == list.end();
}

But gcc return me a segmentation fault surrounding the while line.

Answer 1

Your code will fail if the iterator reaches the last element in the list. When that happens std::next(it) is equal to list.end() and it's an error to dereference an end() iterator (causing a segfault in this case).

My suggestion is to use the std::is_sorted algorithm in the standard library. It's already written, debugged, and does what you want.

template<class T>
bool estTriee(const std::forward_list<T>& list) {
    return std::is_sorted(list.begin(), list.end());
}