你完全正确 vector :: iterator 可以通过简单的指针实现（参见此处） - in事实上，迭代器的概念基于指向数组元素的指针。对于其他容器，例如 map ， list 或 deque ，但是，指针根本不起作用。那为什么不这样做呢？以下是为什么类实现比原始指针更可取的三个原因。

You're completely correct that vector::iterator could be implemented by a simple pointer (see here) -- in fact the concept of an iterator is based on that of a pointer to an array element. For other containers, such as map, list, or deque, however, a pointer won't work at all. So why is this not done? Here are three reasons why a class implementation is preferrable over a raw pointer.

1. 将迭代器实现为单独的类型允许其他功能（超出标准要求的范围），例如（在Quentins注释之后的编辑中添加）在解除引用迭代器时添加断言的可能性，例如，在调试模式下。

1. Implementing an iterator as separate type allows additional functionality (beyond what is required by the standard), for example (added in edit following Quentins comment) the possibility to add assertions when dereferencing an iterator, for example, in debug mode.

重载分辨率如果迭代器是一个指针 T * ，它可以作为有效参数传递给一个函数取 T * ，而迭代器类型则无法实现。因此，使 std :: vector<> :: iterator 指针实际上改变了现有代码的行为。例如，考虑

overload resolution If the iterator were a pointer T*, it could be passed as valid argument to a function taking T*, while this would not be possible with an iterator type. Thus making std::vector<>::iterator a pointer in fact changes the behaviour of existing code. Consider, for example,

template<typename It>
void foo(It begin, It end);
void foo(const double*a, const double*b, size_t n=0);

std::vector<double> vec;
foo(vec.begin(), vec.end());    // which foo is called?

std::vector<double> vec;
sort(vec.begin(), vec.end());             // calls std::sort
sort(vec.data(), vec.data()+vec.size());  // fails to compile