C++ begin() == end() 是否适用于任何 empty() 向量？

Is begin() == end() for any empty() vector?

提问by OldPeculier

I have long assumed that for any empty std::vectorV, V.begin() == V.end(). Yet I see nothing in the C++ specification that states this to alwaysbe true. Is it necessarily true or does it just happen to be true on most implementations?

我长期以来一直假设对于任何空的std::vectorV, V.begin() == V.end(). 然而，我在 C++ 规范中没有看到任何声明这总是正确的。它一定是真的还是碰巧在大多数实现中都是真的？

回答by Rapptz

Yes, that's what the standard requires it to be for empty()for any container.

是的，这就是标准empty()对任何容器的要求。

§ 23.2.1 Table 96 of the C++11 standard says:

C++11 标准的第 23.2.1 节表 96 说：

 +----------+---------------+----------------------+
 |Expression|  Return Type  | Operational Semantics|
 |----------|---------------|----------------------|
 |a.empty() |Convertible    |a.begin() == a.end()  |
 |          |to bool        |                      |
 |          |               |                      |
 +-------------------------------------------------+

回答by juanchopanza

23.2.1 General container requirements, specifically Table 96 Container Requirementshas

23.2.1 一般集装箱要求，特别是表 96集装箱要求有

a.empty()convertible to bool, operational semantics a.begin() == a.end()

a.empty()可转换为bool, 操作语义a.begin() == a.end()

Then

然后

6 begin()returns an iterator referring to the first element in the container. end()returns an iterator which is the past-the-end value for the container. If the container is empty, then begin() == end();

6begin()返回一个引用容器中第一个元素的迭代器。end()返回一个迭代器，它是容器的最后值。如果容器是空的，那么begin() == end();

(emphasis mine)

（强调我的）

回答by Jiminion

http://www.cplusplus.com/reference/vector/vector/end/

http://www.cplusplus.com/reference/vector/vector/end/

If the container is empty, end() is the same as begin().

如果容器为空，则 end() 与 begin() 相同。

回答by Ivan Smirnov

Yes, that is true. Here is the proof. And, of course, std::distance(a.begin(), a.end()) == 0for an empty vector.

是的，这是真的。这是证据。当然，std::distance(a.begin(), a.end()) == 0对于空向量。