如何正确实现自定义迭代器和const_iterators？ | 如何正确实现自定义迭代器和const

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问题描述

我有一个自定义的容器类，我想写入 iterator 和 const_iterator 类。 / p>

我以前从来没有这样做，我找不到合适的方法。关于迭代器创建的指导方针是什么，以及我应该注意什么？

我也希望避免代码重复（我觉得 const_iterator 和迭代器共享许多东西;应该是另一个子类）。

>解决方案

选择适合您的容器的迭代器类型：input，output，forward等。

图书馆。例如， with random_access_iterator_tag 。这些基类定义了STL所需的所有类型定义并执行其他工作。

为避免代码重复，是一个模板类，并由值类型，指针类型，引用类型或所有这些（取决于实现）参数化。例如：
```
  //迭代器类由指针类型参数化
 template< typename PointerType> class MyIterator {
 //迭代器类定义在这里
}; 
 
 typedef MyIterator< int *> iterator_type; 
 typedef MyIterator< const int *> const_iterator_type; 
  
```
注意 iterator_type 和 const_iterator_type 类型定义：它们是非const和const迭代器的类型。

另请参阅：

I have a custom container class for which I'd like to write the iterator and const_iterator classes.

I never did this before and I failed to find an appropriate how-to. What are the guidelines regarding iterator creation, and what should I be aware of ?

I'd also like to avoid code duplication (I feel that const_iterator and iterator share many things; should one subclass the other ?).

Foot note: I'm pretty sure Boost has something to ease this but I can't use it here, for many stupid reasons.

解决方案

Choose type of iterator which fits your container: input, output, forward etc.
Use base iterator classes from standard library. For example, std::iterator with random_access_iterator_tag.These base classes define all type definitions required by STL and do other work.
To avoid code duplication iterator class should be a template class and be parametrized by "value type", "pointer type", "reference type" or all of them (depends on implementation). For example:
```
// iterator class is parametrized by pointer type
template <typename PointerType> class MyIterator {
    // iterator class definition goes here
};

typedef MyIterator<int*> iterator_type;
typedef MyIterator<const int*> const_iterator_type;
```
Notice iterator_type and const_iterator_type type definitions: they are types for your non-const and const iterators.