在 C++ 中为我自己的自定义向量模板类实现迭代器(类似于 STL)[重复]
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【中文标题】在 C++ 中为我自己的自定义向量模板类实现迭代器(类似于 STL)[重复]【英文标题】:implementing an iterator (something like from STL) for my own custom vector template class in C++ [duplicate] 【发布时间】:2021-07-01 14:46:37 【问题描述】:我有一个来自 GeeksforGeeks 网站的自己的容器,我从下面的容器代码中获得。我喜欢创建一个迭代器类,它的功能将使我能够使用for
循环和函数,例如在我的容器中开始和结束,而 for 循环将类似于
MyClassForIterator iter;
for(iter=mycontainer_items_obj.begin();iter!=mycontainer_items_obj.end();iter++)
cout<<*iter<<endl
...
我想知道这在 C++ 中是否可行以及如何实现?
矢量模板类
#include <bits/stdc++.h>
using namespace std;
template <typename T> class vectorClass
// arr is the integer pointer
// which stores the address of our vector
T* arr;
// capacity is the total storage
// capacity of the vector
int capacity;
// current is the number of elements
// currently present in the vector
int current;
public:
// Default constructor to initialise
// an initial capacity of 1 element and
// allocating storage using dynamic allocation
vectorClass()
arr = new T[1];
capacity = 1;
current = 0;
// Function to add an element at the last
void push(T data)
// if the number of elements is equal to the
// capacity, that means we don't have space to
// accommodate more elements. We need to double the
// capacity
if (current == capacity)
T* temp = new T[2 * capacity];
// copying old array elements to new array
for (int i = 0; i < capacity; i++)
temp[i] = arr[i];
// deleting previous array
delete[] arr;
capacity *= 2;
arr = temp;
// Inserting data
arr[current] = data;
current++;
// function to add element at any index
void push(int data, int index)
// if index is equal to capacity then this
// function is same as push defined above
if (index == capacity)
push(data);
else
arr[index] = data;
// function to extract element at any index
T get(int index)
// if index is within the range
if (index < current)
return arr[index];
// function to delete last element
void pop() current--;
// function to get size of the vector
int size() return current;
// function to get capacity of the vector
int getcapacity() return capacity;
// function to print array elements
void print()
for (int i = 0; i < current; i++)
cout << arr[i] << " ";
cout << endl;
;
// Driver code
int main()
vectorClass<int> v;
vectorClass<char> v1;
v.push(10);
v.push(20);
v.push(30);
v.push(40);
v.push(50);
v1.push(71);
v1.push(72);
v1.push(73);
v1.push(74);
cout << "Vector size : " << v.size() << endl;
cout << "Vector capacity : " << v.getcapacity() << endl;
cout << "Vector elements : ";
v.print();
v.push(100, 1);
cout << "\nAfter updating 1st index" << endl;
cout << "Vector elements of type int : " << endl;
v.print();
// This was possible because we used templates
cout << "Vector elements of type char : " << endl;
v1.print();
cout << "Element at 1st index of type int: " << v.get(1)
<< endl;
cout << "Element at 1st index of type char: "
<< v1.get(1) << endl;
v.pop();
v1.pop();
cout << "\nAfter deleting last element" << endl;
cout << "Vector size of type int: " << v.size() << endl;
cout << "Vector size of type char: " << v1.size()
<< endl;
cout << "Vector capacity of type int : "
<< v.getcapacity() << endl;
cout << "Vector capacity of type char : "
<< v1.getcapacity() << endl;
cout << "Vector elements of type int: ";
v.print();
cout << "Vector elements of type char: ";
v1.print();
return 0;
【问题讨论】:
当然可以在 C++ 中使用,但这是一个相当高级、复杂的主题,需要编写大量代码。不幸的是,您不太可能从某些网站或 Youtube 视频中学习这些高级、复杂的 C++ 主题。学习高级 C++ 主题的唯一现实方法是with an advanced C++ textbook。 容器已损坏,因为它没有遵循rule of 3/5。不幸的是,在您找到它的网站上找到相当糟糕的代码并不罕见。标题应该是“如何在 C++ 中实现我们自己完全损坏的向量类?”而不是在最后加上免责声明“注意读者!现在不要停止学习。”免责声明应该在开头说“注意读者!接下来是如何不实现容器”。我不喜欢咆哮,但我不想让你被愚弄 【参考方案1】:是的,在 C++ 中完全可以在你的向量中定义一个嵌套的迭代器类。在这里,我定义了一个前向迭代器,对于您的情况,您可能想要选择不同的类别:
template <typename T> class vectorClass
T* arr;
int capacity;
int current;
public:
struct iterator
// You need these tags to provide introspection and conform
// to standard implementations of iterators. If you were
// using Boost to define your iterator, you'd define those in
// the base class.
using iterator_category = std::forward_iterator_tag;
using difference_type = std::ptrdiff_t;
using value_type = T;
using pointer = value_type*;
using reference = value_type&;
iterator(pointer ptr) : m_ptr(ptr)
reference operator*() const return *m_ptr;
pointer operator->() return m_ptr;
// Prefix increment
iterator& operator++() m_ptr++; return *this;
// Postfix increment
iterator operator++(int)
Iterator tmp = *this; ++(*this); return tmp;
friend bool operator== (const Iterator& a, const Iterator& b)
return a.m_ptr == b.m_ptr; ;
friend bool operator!= (const Iterator& a, const Iterator& b)
return a.m_ptr != b.m_ptr; ;
private:
pointer m_ptr;
;
// Add begin/end functions to your class
iterator begin() return iterator(arr);
iterator end() return iterator(arr + curr);
/*
REST of the class remains the same
*/
;
您可能已经在 cmets 中注意到,我提到了 boost iterator facade library 作为定义迭代器的工具。如果这是您的选择,您可以使用它来消除大部分样板文件。
【讨论】:
如果我在迭代器结构构造函数中尝试pointer ptr
等,您能否添加我需要添加的头文件?
@user786 我想你只需要 #include <iterator>
。您是否从代码中得到错误?
不,我还没有编译它。但我很快就会去做。感谢您的评论
这个类也可以使用push_back函数吗
@user786 当然,迭代器实现只需要你保持arr
和curr
成员的顺序。所以现有的push
(如问题中所写)有效。【参考方案2】:
如果您的容器在内部将其数据存储为 contiguios 数组(就像您的那样),那么您可以简单地使用 pointer 作为迭代器:
template <typename T> class vectorClass
public:
T* begin() return arr;
T* end() return arr + current;
T const* begin() const return arr;
T const* end() const return arr + current;
// ... etc...
;
这是因为 pointer 满足 iterator 的所有要求。事实上,迭代器是指针的泛化。
【讨论】:
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