C++ 迭代通过双链表的前面
my_prev的价值是多少? 它是my_list.rend吗,尽管它在技术上是不同的类型?C++ 迭代通过双链表的前面,c++,list,c++11,iterator,c++-standard-library,C++,List,C++11,Iterator,C++ Standard Library,my_prev的价值是多少? 它是my_list.rend吗,尽管它在技术上是不同的类型? 除了my_iter==my_list.begin之外,如何检查这种情况?根据C++11标准: std::list<my_type> my_list; std::list<my_type>::iterator my_iter = my_list.begin(); std::list<my_type>::iterator my_prev = std::prev(my_ite
除了my_iter==my_list.begin之外,如何检查这种情况?根据C++11标准:
std::list<my_type> my_list;
std::list<my_type>::iterator my_iter = my_list.begin();
std::list<my_type>::iterator my_prev = std::prev(my_iter);
所以,看起来,或者至少我在标准中找不到更相关的部分,这个行为没有定义
我建议您保持这种情况,并在将其传递给std::prev之前小心我的iter值。相关:您是对的,这是未定义的行为。它恰好适用于某些列表实现,但在任何情况下都不是一个好主意。在调用std::prev之前检查参数是否为!=开始
24.4.4 Iterator operations [iterator.operations]
§ 7
template <class BidirectionalIterator>
BidirectionalIterator prev(BidirectionalIterator x,
typename std::iterator_traits<BidirectionalIterator>::difference_type n = 1);
Effects: Equivalent to advance(x, -n); return x;
template <class InputIterator, class Distance>
void advance(InputIterator& i, Distance n);
Requires: n shall be negative only for bidirectional and random access iterators.
Effects: Increments (or decrements for negative n) iterator reference i by n.
24.2.6 Bidirectional iterators
Expression Return type Operational Assertion/note
semantics pre-/post-condition
pre: there exists s such that
--r X& r == ++s.
post: r is dereferenceable.
--(++r) == r.
--r == --s implies r == s.
&r == &--r.