Get index in vector from reverse iterator
来源： https://stackoverflow.com/questions/24997910/get-index-in-vector-from-reverse-iterator
reverse-iterator
Get index in vector from reverse iterator
来源： https://stackoverflow.com/questions/24997910/get-index-in-vector-from-reverse-iterator
Delete rows based on values within cell, optimising
问题 I have script running on a weekly bases deleting rows from a document and then pasting these values to another sheet for data analysis, however as the document grows (+20,0000 rows) my script times out. Anyway on how to optimise the script to perhaps use less processing/memory and run faster? var rowsDeleted = 0; for (var i = 0; i <= numRows - 1; i++) { var row = values[i]; if (row[0] == 'delete' || row[0] == '') { data.deleteRow((parseInt(i)+1) - rowsDeleted); rowsDeleted++; } } 回答1: In your
Why use rbegin() instead of end() - 1?
问题 I'm wondering what the benefits of using rbegin() rather than end() - 1 are for STL containers. For example, why would you use something like: vector<int> v; v.push_back(999); vector<int>::reverse_iterator r = v.rbegin(); vector<int>::iterator i = r.base(); Rather than: vector<int> v; v.push_back(999); auto r = v.end() - 1; 回答1: rbegin() return an iterator with a reverse operator++ ; that is, with a reverse_iterator you can iterate through a container going backward. Example: #include <vector
STL iterator before std::map::begin()
问题 In C++11's std::map , is there some valid iterator x such that ++ x is guaranteed to equal map::begin() ? I would like to detect if a function I just called (mine) has walked an iterator off the front of a function. The function will move the iterator exactly one position backward. Does the answer hold for the rest of the library? 回答1: No, iterators before the beginning in std containers are all UB (except for reverse iterators, which will probably not solve your problem). You probably need
Why does reverse_iterator doubly define its nested types?
问题 It appears that the iterator adaptor reverse_iterator doubly defines most of its nested types. In particular, it inherits publicly from std::iterator which exposes iterator_category , value_type , difference_type , pointer and reference . Except for iterator_category and value_type , these are all explicitly typedef 'ed again in the class definition. 24.5.1.1 Class template reverse_iterator [reverse.iterator] namespace std { template <class Iterator> class reverse_iterator : public iterator
What's the difference between a reversed tuple and a reversed list?
问题 Reversing a tuple and reversing a list returns objects of different type: >>> reversed((1,2)) <reversed at 0x7fffe802f748> >>> reversed([1,2]) <list_reverseiterator at 0x7fffebdd4400> They have the same dir . Neither type is a subclass of the other. Why is that? What can one do that the other can't? 回答1: Basically, a list implements the __reversed__ method and returns an specialized object, while tuple falls back to the default implementation of reversed for any sequence: >>> list.__reversed_
Check if iterator's type is reverse_iterator
问题 Is there a way to check if iterator passed as arg to fnc is reverse_iterator? Are there any iterator traits function I could use? 回答1: It's trivial to write with a partial specialization: #include <iterator> #include <type_traits> template<typename Iter> struct is_reverse_iterator : std::false_type { }; template<typename Iter> struct is_reverse_iterator<std::reverse_iterator<Iter>> : std::true_type { }; Although as pointed out below, this doesn't handle the (IMHO unlikely) case of a "reverse
Why use rbegin() instead of end() - 1?
I'm wondering what the benefits of using rbegin() rather than end() - 1 are for STL containers. For example, why would you use something like: vector<int> v; v.push_back(999); vector<int>::reverse_iterator r = v.rbegin(); vector<int>::iterator i = r.base(); Rather than: vector<int> v; v.push_back(999); auto r = v.end() - 1; rbegin() return an iterator with a reverse operator++ ; that is, with a reverse_iterator you can iterate through a container going backward. Example: #include <vector> #include <iostream> int main() { std::vector<int> v{0,1,2,3,4}; for( auto i = v.rbegin(); i != v.rend(); +
Check if iterator's type is reverse_iterator
Is there a way to check if iterator passed as arg to fnc is reverse_iterator? Are there any iterator traits function I could use? It's trivial to write with a partial specialization: #include <iterator> #include <type_traits> template<typename Iter> struct is_reverse_iterator : std::false_type { }; template<typename Iter> struct is_reverse_iterator<std::reverse_iterator<Iter>> : std::true_type { }; Although as pointed out below, this doesn't handle the (IMHO unlikely) case of a "reverse-reverse" iterator. The slightly less trivial version in Bathsheba's answer handles that case correctly. Some