C++中有没有标准的循环迭代器？
C++中有没有标准的循环迭代器？
提问于 2010-04-11 17:59:41
基于以下问题：Check if one string is a rotation of other string
我在考虑做一个带范围的循环迭代器类型，可以像这样解决上面的问题：
std::string s1 = "abc" ;
std::string s2 = "bca" ;
std::size_t n = 2; // number of cycles
cyclic_iterator it(s2.begin(),s2.end(),n);
cyclic_iterator end;
if (std::search(it, end, s1.begin(),s1.end()) != end)
{
std::cout << "s1 is a rotation of s2" << std::endl;
}我的问题是，已经有类似的东西可用了吗？我已经检查了Boost和STL，它们都没有确切的实现。
我有一个简单的手写版本(从std::iterator的std::forward_iterator_tag专用版派生而来)，但我更愿意使用已经制作/测试的实现。
回答 5
Stack Overflow用户
发布于 2012-02-07 04:48:37
这应该会提供一些想法/解决方案:2个格式，第二个稍微轻一点。两者都使用向量和列表的子范围进行了测试...
#include <vector>
template <typename T, typename Container = std::vector<T>, typename Iterator = Container::iterator>
class RingIterator : public std::iterator <std::bidirectional_iterator_tag, T, ptrdiff_t>
{
Container& data;
Iterator cursor;
Iterator begin;
Iterator end;
public:
RingIterator (Container& v) : data(v), cursor(v.begin()), begin(v.begin()), end(v.end()) {}
RingIterator (Container& v, const Iterator& i) : data(v), cursor(i), begin(v.begin()), end(v.end()) {}
RingIterator (Container& v, const Iterator& i, const Iterator& j) : data(v), cursor(i), begin(i), end(j) {}
RingIterator (Container& v, size_t i) : data(v), cursor(v.begin() + i % v.size()), begin(v.begin()), end(v.end()) {}
bool operator == (const RingIterator& x) const
{
return cursor == x.cursor;
}
bool operator != (const RingIterator& x) const
{
return ! (*this == x);
}
reference operator*() const
{
return *cursor;
}
RingIterator& operator++()
{
++cursor;
if (cursor == end)
cursor = begin;
return *this;
}
RingIterator operator++(int)
{
RingIterator ring = *this;
++*this;
return ring;
}
RingIterator& operator--()
{
if (cursor == begin)
cursor = end;
--cursor;
return *this;
}
RingIterator operator--(int)
{
RingIterator ring = *this;
--*this;
return ring;
}
RingIterator insert (const T& x)
{
return RingIterator (data, data.insert (cursor, x));
}
RingIterator erase()
{
return RingIterator (data, data.erase (cursor));
}
};
template <typename T, typename Iterator>
class CyclicIterator : public std::iterator <std::bidirectional_iterator_tag, T, ptrdiff_t>
{
Iterator cursor;
Iterator begin;
Iterator end;
public:
CyclicIterator (const Iterator& i, const Iterator& j) : cursor(i), begin(i), end(j) {}
bool operator == (const CyclicIterator& x) const
{
return cursor == x.cursor;
}
bool operator != (const CyclicIterator& x) const
{
return ! (*this == x);
}
reference operator*() const
{
return *cursor;
}
CyclicIterator& operator++()
{
++cursor;
if (cursor == end)
cursor = begin;
return *this;
}
CyclicIterator operator++(int)
{
CyclicIterator ring = *this;
++*this;
return ring;
}
CyclicIterator& operator--()
{
if (cursor == begin)
cursor = end;
--cursor;
return *this;
}
CyclicIterator operator--(int)
{
CyclicIterator ring = *this;
--*this;
return ring;
}
};
#include <iostream>
#include <iomanip>
#include <list>
enum { CycleSize = 9, ContainerSize };
template <typename cyclicIterator>
void test (cyclicIterator& iterator, size_t mn)
{
int m = mn;
while (m--)
for (int n = mn; n--; ++iterator)
std::cout << std::setw(3) << *iterator << ' ';
--iterator;
m = mn;
while (m--)
for (int n = mn; n--; --iterator)
std::cout << std::setw(3) << *iterator << ' ';
}
template <typename containers>
void load (containers& container)
{
while (container.size() < ContainerSize)
container.push_back (container.size());
}
void main (void)
{
typedef std::vector<int> vContainer;
typedef vContainer::iterator vIterator;
typedef std::list<int> lContainer;
typedef lContainer::iterator lIterator;
vContainer v; load (v);
vIterator vbegin = v.begin() + 1;
RingIterator <int, vContainer, vIterator> vring (v, vbegin, v.end());
CyclicIterator <int, vIterator> vcycle (vbegin, v.end());
lContainer l; load (l);
lIterator lbegin = l.begin(); ++lbegin;
RingIterator <int, lContainer, lIterator> lring (l, lbegin, l.end());
CyclicIterator <int, lIterator> lcycle (lbegin, l.end());
test (vring, CycleSize);
test (vcycle, CycleSize);
test (lring, CycleSize);
test (lcycle, CycleSize);
}Stack Overflow用户
发布于 2016-08-13 16:14:45
CGAL库定义了Circulators。它们是这样使用的。
template<class Circulator, class T>
bool contains(Circulator c, Circulator d, const T& value) {
if (c != 0) {
do {
if (*c == value)
return true;
} while (++c != d);
}
return false;
} 注意，乍一看，它们看起来像迭代器，但注意逻辑(和循环结构)与迭代器不同。if(not empty) do{..}while()而不是while(){...}。
Stack Overflow用户
发布于 2010-04-11 21:02:35
您可能正在寻找Boost的Circular Buffer。但是如果你已经检查了Boost，它可能不是你想要的。
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/2616643
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