是std :: vector :: begin() - 1未定义? [英] Is std::vector::begin() - 1 undefined?
问题描述
我需要以向后的顺序迭代一些元素并且我正在使用:
I need to iterate over some elements in backward order and I'm using:
for ( /* ... */ it = vec.end() - 1, end = vec.begin() ; it >= end ; --it ) {
// ...
我现在 end() - 1
是为某些容器定义的,包括vector,但是现在我需要知道是否还定义了开始减量。
I now that end() - 1
is defined for some containers, including vector, but now I need to know if begin decrement is also defined.
我不知道我是否可以使用reverse_iterator,因为我需要将这些迭代器作为参数传递给std :: vector :: erase,并且从文档中看,它们看起来是不同的类型。
I don't know if I could use reverse_iterator, because I'll need to pass these iterators as parameters to std::vector::erase and from the documentation, it looks that they are different types.
推荐答案
是的,它是未定义的。
如果你想反向迭代元素,只需使用 rb egin
和 雷德
。它们是反向迭代器,专门为此目的而设计。如果需要从反向迭代器获取标准迭代器,可以使用 <$迭代器上的c $ c> base 成员函数。
If you want to iterate over elements in reverse, just use rbegin
and rend
. They're reverse iterators, designed explicitly for this purpose. If you need to get a standard iterator from the reverse iterator, you can use the base
member function on the iterator.
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