Related specifically to iterators that traverses a container in reverse order. An iterator is an object-oriented programming pattern that allows traversal through a collection, agnostic of the actual implementation or object addresses in physical memory.
Questions tagged [reverse-iterator]
82 questions
21
votes
2 answers
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 v;
v.push_back(999);
vector::reverse_iterator r = v.rbegin();
vector::iterator i =…
Victor Brunell
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20
votes
2 answers
What's the difference between a reversed tuple and a reversed list?
Reversing a tuple and reversing a list returns objects of different type:
>>> reversed((1,2))
>>> reversed([1,2])
They have the same dir. Neither type is a subclass of the…
wim
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19
votes
3 answers
Get index in vector from reverse iterator
I know how to get the index from a vector iterator, by subtracting the begin iterator from it. For example:
vector::iterator it = find(vec.begin(), vec.end(), x);
size_t position = it - vec.begin();
However, now I want to find the index of the…
Neil Kirk
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17
votes
4 answers
Exposition only in the C++ standard?
What does exposition only exactly means in the C++ standard? Does it mean that the private/protected members marked exposition only are required to exist by standard, or are they just a "suggestion" of implementation, and are not required at…
Vincent
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14
votes
1 answer
How do you use find_if along with reverse_iterator on a C-style array?
To search the first occurence of a element in a C-Array with POD elements, one ease can do this with std::find_if(begin, end, findit). But I needed the last occurence. This answer gave me the idea that this can be done with std::reverse_iterator.…
Christian Ammer
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13
votes
2 answers
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?
There is nothing we can do
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13
votes
3 answers
Is it safe to use std::prev(vector.begin()) or std::next(vector.begin(), -1) like some_container.rend() as reversed sentry?
I wrote some code that takes iterators but have to do comparison in reversed order,
template
bool func(ConstBiIter seq_begin, ConstBiIter seq_end)
{
ConstBiIter last = std::prev(seq_end);
while (--last !=…
dguan
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12
votes
1 answer
One variable for either iterator or reverse_iterator?
I want to iterate through some std::vectors in a for loop but depending on some conditions, the vectors shall be iterated either forward or backward. I thought, I could easily do it by using either normal iterators or reverse iterators like…
Sven Hoek
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11
votes
1 answer
Erasing element from a vector – rbegin() vs begin()
I'm trying to solve a problem in C++, a part of which requires me to erase elements from a vector using the rbegin() member function. However, the compiler throws an error every time I write the below-mentioned code. What's wrong here?
int main()…
RedHelmet
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11
votes
2 answers
Why does reverse_iterator doubly define its nested types?
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…
TemplateRex
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11
votes
1 answer
Why does removing the _first_ element of a list invalidate `.rend()`?
Tested on Mac OS X using XCode 4.6.
This example code shows removing the last element of an std::list works as I expected: an iterator reference to list::end() is still "1 past the end" and is still valid, even through removal of the last…
bobobobo
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10
votes
1 answer
reverse_iterator weird behavior with 2D arrays
I have a 2D array. It's perfectly okay to iterate the rows in forward order, but when I do it in reverse, it doesn't work. I cannot figure out why.
I'm using MSVC v143 and the C++20 standard.
int arr[3][4];
for (int counter = 0, i = 0; i != 3; ++i)…
Seideun
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10
votes
1 answer
Reverse iteration in Julia
Yesterday I had occasion to want to iterate over a collection in reverse order. I found the reverse function, but this does not return an iterator, but actually creates a reversed collection.
Apparently, there used to be a Reverse iterator, which…
DNF
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10
votes
3 answers
STL iterator before std::map::begin()
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…
George Hilliard
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7
votes
1 answer
What C++20 change to reverse_iterator is breaking this code?
The following code compiles in C++11, C++14, and C++17, but does not compile in C++20. What change to the standard broke this code?
#include
#include
template
struct bar
{
typename T::reverse_iterator…
Pubby
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