iterator

问题 Why do I need to dereference iterators? For example in the following program #include <iostream> #include <string> #include <vector> int main() { using namespace std; string s("some string"); for(auto it = s.begin(); it != s.end(); && !isspace(*it); ++it) *it = isupper(*it); cout<<s; } Why is it necessary to use isupper(*it); instead of just isupper(it); ? 回答1: Iterator is a generalized pointer. It points to something. If you have a function that needs that something(char or int, in this case

问题 Why do I need to dereference iterators? For example in the following program #include <iostream> #include <string> #include <vector> int main() { using namespace std; string s("some string"); for(auto it = s.begin(); it != s.end(); && !isspace(*it); ++it) *it = isupper(*it); cout<<s; } Why is it necessary to use isupper(*it); instead of just isupper(it); ? 回答1: Iterator is a generalized pointer. It points to something. If you have a function that needs that something(char or int, in this case

问题 I use the list iterator of Java, and I don't understand how does the previous method work. I get the next element of the Linked list "B" and then I try to get the previous element "A" but I get "B". LinkedList<Character> abc = new LinkedList<Character>(); abc.add('A'); abc.add('B'); ListIterator<Character> iterator = abc.listIterator(); System.out.println(iterator.next()); System.out.println(iterator.next()); System.out.println(iterator.previous()); The output is "A", "B", "B". Why doesn't it

问题 There are some related questions on Stack but I wanted to be as clear as possible. I am using Python 3 If I have a list, N , and I use the following code: N = [1,2,3,4,6,7,8] for x in N: N[x] = N[x] * -1 return N I am getting a Index out of range error . I understand you shouldn't be adding and deleting elements while iterating over a list, but I wanted a clear definition of why the above example won't work.To me, it seems like there shouldn't be a problem. In the first iteration, x should

问题 How to split an iterator into a prefix with duplicates and the rest ? For instance, def splitDupes(it: Iterator[Int]): (Iterator[Int], Iterator[Int]) = ??? val (xs, ys) = splitDupes(List(1, 1, 1, 2, 3, 4, 5).iterator) xs.toList // List(1, 1, 1) ys.toList // List(2, 3, 4, 5) val (xs, ys) = splitDupes(List(1, 2, 3, 4, 5).iterator) xs.toList // List(1) ys.toList // List(2, 3, 4, 5) val (xs, ys) = splitDupes(List(1, 1, 1, 1, 1).iterator) xs.toList // List(1, 1, 1, 1, 1) ys.toList // List() val

问题 How to split an iterator into a prefix with duplicates and the rest ? For instance, def splitDupes(it: Iterator[Int]): (Iterator[Int], Iterator[Int]) = ??? val (xs, ys) = splitDupes(List(1, 1, 1, 2, 3, 4, 5).iterator) xs.toList // List(1, 1, 1) ys.toList // List(2, 3, 4, 5) val (xs, ys) = splitDupes(List(1, 2, 3, 4, 5).iterator) xs.toList // List(1) ys.toList // List(2, 3, 4, 5) val (xs, ys) = splitDupes(List(1, 1, 1, 1, 1).iterator) xs.toList // List(1, 1, 1, 1, 1) ys.toList // List() val

问题 I want to create a range -like construct in c++, that will be used like this: for (auto i: range(5,9)) cout << i << ' '; // prints 5 6 7 8 for (auto i: range(5.1,9.2)) cout << i << ' '; // prints 5.1 6.1 7.1 8.1 9.1 Handling the integer case is relatively easy: template<typename T> struct range { T from, to; range(T from, T to) : from(from), to(to) {} struct iterator { T current; T operator*() { return current; } iterator& operator++() { ++current; return *this; } bool operator==(const

问题 I want to create a range -like construct in c++, that will be used like this: for (auto i: range(5,9)) cout << i << ' '; // prints 5 6 7 8 for (auto i: range(5.1,9.2)) cout << i << ' '; // prints 5.1 6.1 7.1 8.1 9.1 Handling the integer case is relatively easy: template<typename T> struct range { T from, to; range(T from, T to) : from(from), to(to) {} struct iterator { T current; T operator*() { return current; } iterator& operator++() { ++current; return *this; } bool operator==(const

问题 I want to write a generic function that takes any immutably borrowed iterable container such as an array, Vec , BTreeSet , etc. Since this function is part of a trait that I am implementing, I am not able to change the signature of it, so it's not possible to directly take an iterator as parameter and I also can't introduce any lifetime parameters to the function signature. Context I tried to implement the observer pattern in Rust. The observable and the observer look as follows: struct

问题 I want to write a generic function that takes any immutably borrowed iterable container such as an array, Vec , BTreeSet , etc. Since this function is part of a trait that I am implementing, I am not able to change the signature of it, so it's not possible to directly take an iterator as parameter and I also can't introduce any lifetime parameters to the function signature. Context I tried to implement the observer pattern in Rust. The observable and the observer look as follows: struct