c++ - `iterator` 和 `const_iterator` 不是 STL 容器的必需成员吗？

Question

取自 Understanding iterator/const_iterator implementation :

"although iterator and const_iterator are types declared in the scope of vector, there is no requirement that vector(or any STL container) have a member of either type - iterator and const_iterator are part of the interface of std::vector e.g. overloads of the member begin() returns those types, but nothing is said about how those function obtain the iterator they return"

Additionally STL containers must have:

"a begin and end function that returns iterators"

上面指出iterator和const_iterator不是 STL 容器的必需成员，例如 vector 。我认为这意味着从 .begin 返回的类型或.end根据实现情况会有所不同。

所以我想知道为什么这没有问题，因为我看到很多人写出 std::vector<someType>::iterator或std::vector<someType>::const_iterator哪里iterator和const_iterator指定而不是使用 auto例如:

for (std::vector<int>::iterator i = s.begin(); i != s.end(); i++)
{

}

Answer 1

您读错了引文。该人说

have a member of either type

不是

have either type

当他们说拥有任一类型的成员时，他们的意思是类中没有iterator或const_iterator类型的数据成员。

他们确实接着说

iterator and const_iterator are part of the interface of std::vector

这是正确的，因为标准要求 std::vector 在其接口(interface)中显示这些类型。