[英]Reverse Iterator Arithmetic
All, I'm trying to do an O(n^2) comparison between elements in a list in reverse, so I'm using a reverse iterator. 全部,我试图反向执行列表中元素之间的O(n ^ 2)比较,所以我正在使用反向迭代器。
Code follows 代码如下
#include <list>
struct Element {
double a;
double b;
};
typedef std::list<Element> ElementList;
class DoStuff {
public:
DoStuff();
void removeDuplicates(ElementList & incList) const {
for(ElementList::reverse_iterator stackIter = incList.rbegin(); stackIter != incList.rend(); ++stackIter) {
bool uniqueElement = true;
for(ElementList::reverse_iterator searchIter = stackIter+1; searchIter != incList.rend() && uniqueElement; ++searchIter) {
//Check stuff and make uniqueElement = true;
}
}
}
};
int main() {
std::list<Element> fullList;
DoStuff foo;
foo.removeDuplicates(fullList);
}
I get a compile error on the searchIter
creation... why... 我在searchIter
创建时遇到编译错误...为什么...
This works, but its stupid to read: 这行得通,但其愚蠢之处在于:
ElementList::reverse_iterator searchIter = stackIter;
searchIter++;
for( ; searchIter != incList.rend() && uniqueElement; ++searchIter) {
}
Error below: 错误如下:
In file included from /usr/local/include/c++/6.1.0/bits/stl_algobase.h:67:0,
from /usr/local/include/c++/6.1.0/list:60,
from main.cpp:1:
/usr/local/include/c++/6.1.0/bits/stl_iterator.h: In instantiation of 'std::reverse_iterator<_Iterator> std::reverse_iterator<_Iterator>::operator+(std::reverse_iterator<_Iterator>::difference_type) const [with _Iterator = std::_List_iterator<Element>; std::reverse_iterator<_Iterator>::difference_type = long int]':
main.cpp:16:66: required from here
/usr/local/include/c++/6.1.0/bits/stl_iterator.h:233:41: error: no match for 'operator-' (operand types are 'const std::_List_iterator<Element>' and 'std::reverse_iterator<std::_List_iterator<Element> >::difference_type {aka long int}')
{ return reverse_iterator(current - __n); }
The syntax it + n
for some iterator it
and integer n
requires the iterator to be a "random access iterator". 语法it + n
一些迭代it
和整数n
要求迭代器是一个“随机访问迭代器”。 List iterators do not fulfill that requirement. 列表迭代器不满足该要求。
To get around the "stupid to read" issue, you can use std::next
: 要解决“阅读笨拙”的问题,可以使用std::next
:
for(ElementList::reverse_iterator searchIter = std::next(stackIter); ...
Or, with less typing: 或者,输入更少:
for(auto searchIter = std::next(stackIter); ...
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