STL的前和后增量运算符之间的概念差异 [英] Concept difference between pre and post increment operator for STL

问题描述

假设为：

for (vector<int>::iterator iter = ivec.begin(); iter != ivec.end(); ++iter)
{}

对于 int 等内置类型的前/后增量，但是在迭代器方面， ++ iter 和 iter ++ ？ （请记住，我知道两者在这里都产生相同的结果）。

I do understand the difference when it comes to pre/post increment for built-in types like int etc but in terms of an iterator, what's the difference here between ++iter and iter++? (Bear in mind that I do know that both yield the same result here).

推荐答案

区别是他们不会相同的结果，而这个特定的例子将做同样的，不管使用的增量形式。预递增形式首先递增该值，然后返回它;而后递增形式递增结果，但返回递增之前的值。这对于基本类型通常是无成本的，但是对于像迭代器这样的东西，它需要创建一个临时值来保存未递增的值，以便以后返回。

The difference is they do not yield the same result, while this particular example will do the same regardless of the increment form used. The pre-increment form first increments the value, and then returns it; while the post-increment form increments the result but returns the value previous to incrementation. This is usually a no cost for fundamental types, but for things like iterators it requires creating a temporary value to hold the non-incremented value, in order to be later returned.

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