为什么C ++迭代器不是指针，却可以取消引用? [英] Why can a C++ iterator be dereferenced although it isn't a pointer?

问题描述

我正在阅读C ++ Primer 5th，遇到的代码看起来像这样:

I'm reading C++ Primer 5th, and I encounter code that looks like this:

    string s("some string");
    if (s.begin() != s.end())
    {
      auto it = s.begin();   
      *it = toupper(*it);
    }

it从迭代器接收到字符串s中第一个字符的值；然后用toupper()将其更改为大写. it如何可以取消引用?不应该只是一个char类型的变量而不是一个指针吗?

it receives a value from the iterator to the first character in string s; it is then changed to upper case by toupper(). How is it that it can be dereferenced? Shouldn't it just be a char type variable and not a pointer?

推荐答案

it是迭代器:

在C ++中，迭代器是指向对象中某个元素的任何对象. 一定范围的元素(例如数组或容器)具有 使用一组运算符迭代该范围的元素 (至少是递增(++)和取消引用(*)运算符.)

In C++, an iterator is any object that, pointing to some element in a range of elements (such as an array or a container), has the ability to iterate through the elements of that range using a set of operators (at least, the increment (++) and dereference (*) operators).

最明显的迭代器形式是指针:指针可以指向 数组中的元素，并可以使用增量迭代它们 运算子(++).但是存在其他形式的迭代器.例如，每个 容器类型(例如向量)具有特定的迭代器类型 旨在以有效的方式遍历其元素.

The most obvious form of iterator is a pointer: A pointer can point to elements in an array, and can iterate through them using the increment operator (++). But other forms of iterators exist. For example, each container type (such as a vector) has a specific iterator type designed to iterate through its elements in an efficient way.

请注意，尽管指针是迭代器的一种形式，但并非所有迭代器 具有与指针相同的功能；区分 迭代器对特定算法的要求，五个 存在不同的迭代器类别:

Notice that while a pointer is a form of iterator, not all iterators have the same functionality a pointer has; To distinguish between the requirements an iterator shall have for a specific algorithm, five different iterator categories exist:

由于迭代器是行为类似于指针的智能对象(最初指向字符串的开头-这是

Since an iterator is a smart object that behaves like a pointer (initially pointing to the beginning of the string - which is a container), and iterates over that container, it can be dereferenced, as shown in your code sample. Hence, in general it can be used as pointer.

在您的情况下，将指针在字符串中的当前位置分配为与该位置的 相同的大写字母:

Which, in your case, the current position of the pointer in the string is being assigned to the uppercase equivalent of what it was at that position:

*it = toupper(*it);

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