const_iterator 和 iterator 有什么区别? [英] what is the difference between const_iterator and iterator?

问题描述

这两者在 STL 内部实现有什么区别.性能有什么区别?我想当我们以只读方式"遍历向量时，我们更喜欢 const_iterator，对吧?

What is difference between these two regarding implementation inside STL. what is the difference regarding performance? I guess when we are traversing the vector in "read only wise", we prefer const_iterator, right?

谢谢.

推荐答案

没有性能差异.

const_iterator 是一个指向 const 值的迭代器(就像一个 const T* 指针)；取消引用它返回对常量值的引用(const T&)并防止修改引用的值:它强制执行 const-正确性.

A const_iterator is an iterator that points to const value (like a const T* pointer); dereferencing it returns a reference to a constant value (const T&) and prevents modification of the referenced value: it enforces const-correctness.

当你有一个const引用容器时，你只能得到一个const_iterator.

When you have a const reference to the container, you can only get a const_iterator.

我提到const_iterator 返回常量指针"这是不准确的，感谢 Brandon 指出.

Edited: I mentionned "The const_iterator returns constant pointers" which is not accurate, thanks to Brandon for pointing it out.

对于 COW 对象，获取非常量迭代器(或取消引用它)可能会触发复制.(std::string 的一些过时和现在不允许的实现使用 COW.)

For COW objects, getting a non-const iterator (or dereferencing it) will probably trigger the copy. (Some obsolete and now disallowed implementations of std::string use COW.)

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