C++ STL 适配器

本文主要是介绍C++ STL 适配器，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

系列文章目录

模板特例化，偏特化，左右值引用 https://blog.csdn.net/surfaceyan/article/details/126794013
C++ STL 关联容器 https://blog.csdn.net/surfaceyan/article/details/127414434
C++ STL 序列式容器(二) https://blog.csdn.net/surfaceyan/article/details/127083966
C++ STL 序列式容器(一) https://blog.csdn.net/surfaceyan/article/details/126860166
C++STL迭代器iterator设计 https://blog.csdn.net/surfaceyan/article/details/126772555
C++11 标准库头文件模拟实现,无锁STL https://blog.csdn.net/surfaceyan/article/details/126772555

文章目录

系列文章目录
前言
概念分类
- 容器适配器
- 迭代器适配器
- - 1. insert iterators
  - 2. reverse iterators
  - 3. stream iterators
function adapters
- 4. 用于函数指针：ptr_fun
- 5. 用于成员函数指针： mem_fun, mem_fun_ref
总结

前言

适配器（adapters）在STL组件的灵活组合运用上扮演者重要角色。Adapter这个概念源于23个设计模式中的一个：将一个class的接口转换为以一个class接口，使原本因接口不兼容而不能合作的classes可以一起运作。

实际上就是在原有的接口上再套一层接口
或许叫接口适配器或者接口层也可

概念分类

改变函数对象接口的称为function adapter，改变容器接口的称为 container adapter, 改变迭代器接口的称为 iterator adapter。

queue和stack就是容器适配器。

容器适配器和迭代器适配器

#include <iterator>
#include <deque>
#include <algorithm>
#include <iostream>
using namespace std;int main(int argc, char* argv[])
{ostream_iterator<int> outite(cout, " ");int ia[] = {0,1,2,3,4,5};deque<int> id(ia, ia+6);copy(id.begin(), id.end(), outite);cout << endl;copy(ia+1, ia+2, front_inserter(id));copy(ia+3, ia+4, back_inserter(id));copy(id.begin(), id.end(), outite);cout << endl;deque<int>::iterator ite = find(id.begin(), id.end(), 5);copy(ia+0, ia+3, inserter(id, ite));copy(id.begin(), id.end(), outite);cout << endl;copy(id.rbegin(), id.rend(), outite);cout << endl;istream_iterator<int> inite(cin), eos;  // end-of-streamcopy(inite, eos, inserter(id, id.begin()));copy(id.begin(), id.end(), outite);cout << endl;
}

应用于函数的适配器
所有期望获取适配能力的组件，本事必须是可适配的，也就是说，一元仿函数必须继承自 unary_function，二元仿函数必须继承自 binary_function ，成员函数必须以mem_fun处理过，一般函数必须以 ptr_fun 处理过，一个未经ptr_fun处理的一般函数，虽然也可以函数指针的形式传递STL算法使用，却无法有任何适配能力

void print(int i)
{cout << i << ' ';
}
class Int
{
private:int m_i;
public:explicit Int(int i) : m_i(i) {}~Int() {}void print1() const {cout << '[' << m_i << ']';}
};template<class Arg, class Result>
struct unary_function 
{typedef Arg     argument_type;typedef Result    result_type;
};template <class Arg1, class Arg2, class Result>
struct binary_function
{typedef Arg1   first_argument_type;typedef Arg2  second_argument_type;typedef Result         result_type;
};stringstream scout;ostream_iterator<int> outite(scout, " ");int ia[6] = {2, 21, 12, 7, 19, 23};vector<int> iv(ia, ia+6);cout << count_if(iv.begin(), iv.end(), [](int a)->bool {return a>=12;});cout << endl;transform(iv.begin(), iv.end(), outite, [](int a)->int {return (a+2)*3;});cout << scout.str() << endl;copy(iv.begin(), iv.end(), outite);cout << scout.str() << endl;for_each(iv.begin(), iv.end(), print);cout << endl;for_each(iv.begin(), iv.end(), ptr_fun(print));cout << endl;for_each(iv.begin(), iv.end(), bind(print, placeholders::_1));cout << endl; Int t1(3), t2(7), t3(20), t4(14), t5(68);vector<Int> Iv;Iv.push_back(t1);Iv.push_back(t2);Iv.push_back(t3);Iv.push_back(t4);Iv.push_back(t5);for_each(Iv.begin(), Iv.end(), mem_fun_ref(&Int::print1));  // 私有成员函数必须用指针cout << endl;for_each(Iv.begin(), Iv.end(), bind(&Int::print1, placeholders::_1));cout << endl;

其中std::bind是更易于使用更通用的方法，用它！

容器适配器

template<typename T, typename Sequence = deque<T>>
class stack{
protected:Sequence c;...
};

迭代器适配器

由用户指定一个容器，在调用迭代器适配器时调用指定容器的对应方法

1. insert iterators

可细分为back insert iterator, front insert iterator和insert iterator，分别将对应类型的“指针解引用并赋值”(*p = value)操作修改为对应容器的方法

template<class Container>
class back_insert_iterator
{
protected:Container* container;
public:typedef std::output_iterator_tag iterator_category;typedef void                       value_type;typedef void                  difference_type;typedef void                          pointer;typedef void                        reference;explicit back_insert_iterator(Container& x) : container(&x) {};back_insert_iterator& operator=(const typename Container::value_type& value){container->push_back(value);return *this;}back_insert_iterator& operator*() {return *this;}back_insert_iterator& operator++() {return *this;}back_insert_iterator& operator++(int) {return *this;}
};
template <class Container>
class front_insert_iterator
{
protected:Container* container;
public:typedef std::output_iterator_tag iterator_category;typedef void                       value_type;typedef void                  difference_type;typedef void                          pointer;typedef void                        reference;explicit front_insert_iterator(Container& c) : container(&c) {}front_insert_iterator& operator=(const typename Container::value_type& v){container->push_front(v);return *this;}front_insert_iterator& operator*() {return *this;}front_insert_iterator& operator++() {return *this;}front_insert_iterator& operator++(int) {return *this;}
};
template <class Container>
class insert_iterator
{
protected:Container* container;typename Container::iterator iter;
public:typedef std::output_iterator_tag iterator_category;typedef void                       value_type;typedef void                  difference_type;typedef void                          pointer;typedef void                        reference;explicit insert_iterator(Container& c, typename Container::iterator i) : container(&c), iter(i) {}insert_iterator& operator=(const typename Container::value_type& v){iter = container->insert(iter, v);++iter;return *this;}insert_iterator& operator*() {return *this;}insert_iterator& operator++() {return *this;}insert_iterator& operator++(int) {return *this;}
};template <class Container>
inline back_insert_iterator<Container> back_inserter(Container& x)
{return back_insert_iterator<Container>(x);
}
template <class Container>
inline front_insert_iterator<Container> front_inserter(Container& x)
{return front_insert_iterator<Container>(x);
}
template <class Container, class Iterator>
inline insert_iterator<Container> inserter(Container& x, Iterator i)
{typedef typename Container::iterator iter;return insert_iterator<Container>(x, iter(i));
}int main()
{std::deque<int> v{1,2,3};auto bins = ::front_inserter(v);*bins = 4;*bins = 6;std::ostream_iterator<int> outite(std::cout, " ");std::copy(v.begin(), v.end(), outite); std::cout << std::endl;
}

2. reverse iterators

和reverse_iterator迭代器相关，将移动操作倒转
copy(v.rbegin(), v.rend(), ite)看似简单，实则暗藏玄机

typedef reverse_iterator<iterator> reverse_iterator;
reverse_iterator rbegin() {return reverse_iterator(end());}
reverse_iterator rend() {return reverse_iterator(begin());}

在这里插入图片描述


template <class Iterator>
class reverse_iterator
{
protected:Iterator current;  // 记录对应之正向迭代器
public:typedef typename std::iterator_traits<Iterator>::iterator_category  iterator_category;typedef typename std::iterator_traits<Iterator>::value_type                value_type;typedef typename std::iterator_traits<Iterator>::difference_type      difference_type;typedef typename std::iterator_traits<Iterator>::pointer                      pointer;typedef typename std::iterator_traits<Iterator>::reference                  reference;typedef Iterator          iterator_type;typedef reverse_iterator<Iterator> self;reverse_iterator() {}explicit reverse_iterator(iterator_type x) : current(x) {}reverse_iterator(const self& x): current(x.current) {}iterator_type base() const {return current;}reference operator*() const{Iterator tmp = current;return *--tmp;  // key point}pointer operator->() const {return &(operator*());}self& operator++(){--current;return *this;}self operator++(int){self tmp = *this;--current;return tmp;}self& operator--(){++current;return *this;}self operator--(int){self tmp = *this;++current;return tmp;}self operator+(difference_type n) const{return self(current - n);}self& operator+=(difference_type n){current -= n;return *this;}self operator-(difference_type n) const{return self(current + n);}self& operator-=(difference_type n){current += n;return *this;}difference_type operator-(const self& second) const{return second.current - current;}reference operator[](difference_type n) const {return *(*this+n);}
};int main()
{std::deque<int> v{1,2,3};::reverse_iterator<std::deque<int>::iterator> rbegin(v.end()), rend(v.begin());std::ostream_iterator<int> outite(std::cout, " ");// copy到outite迭代器所指的位置std::copy(rbegin, rend, outite); std::cout << std::endl;
}

3. stream iterators

就是将迭代器绑定到一个stream对象身上。绑定到istream(std::cin)身上叫istream_iterator，拥有输入能力；绑定到ostream(std::cout)身上的叫ostream_iterator, 拥有输出能力。
所谓绑定是指，在iterator内部维护一个stream成员，客户端对该iterator的所有操作都转换成该stream成员的操作。

template <typename T, typename Distance = std::ptrdiff_t>
class istream_iterator
{
friend bool operator==(const istream_iterator<T, Distance>& x, const istream_iterator<T, Distance>& y);protected:std::istream* stream;T value;bool end_marker;void read(){end_marker = (*stream) ? true : false;if (end_marker) *stream >> value;end_marker = (*stream) ? true : false;}
public:typedef std::input_iterator_tag  iterator_category;typedef T                               value_type;typedef Distance                   difference_type;typedef const T*                           pointer;typedef const T&                         reference;istream_iterator() : stream(&std::cin), end_marker(false) {}explicit istream_iterator(std::istream& s) : stream(&s) { read(); }reference operator*() const { return value; }pointer operator->() const { return &(operator*()); }istream_iterator& operator++(){read();return *this;}istream_iterator operator++(int){istream_iterator<T, Distance> tmp = *this;read();return tmp;}
};

template <typename T>
class ostream_iterator
{
protected:std::ostream* stream;const char* string;
public:typedef std::output_iterator_tag  iterator_category;typedef void                             value_type;typedef void                        difference_type;typedef void                                pointer;typedef void                              reference;explicit ostream_iterator(std::ostream& s) : stream(&s), string(0) {}ostream_iterator(std::ostream& s, const char* c) : stream(&s), string(c) {}ostream_iterator operator=(const T& value){*stream << value;if (string) *stream << string;return *this;}ostream_iterator& operator*() {return *this;}ostream_iterator& operator++() {return *this;}ostream_iterator& operator++(int) {return *this;}
};

以上两个迭代器在应用上非常重要，说明了如何为自己量身定制一个迭代器。可以完成一个绑定到 Internet Explorer 身上的迭代器，也可以完成一个绑定到磁盘目录上的迭代器······

function adapters

std::bind

4. 用于函数指针：ptr_fun

@deprecated Deprecated in C++11, no longer in the standard since C++17.

5. 用于成员函数指针： mem_fun, mem_fun_ref

在这里插入图片描述
@deprecated Deprecated in C++11, no longer in the standard since C++17. Use mem_fn instead.

std::mem_fn

总结

algorithm里存放各种算法如accumulate，sort等
functional里存各种xx函数如std::move, less, greater等

适配器一般要和泛型算法配合使用方可体现其强大之处

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C++ STL 适配器

系列文章目录

文章目录

前言

概念分类

容器适配器

迭代器适配器

1. insert iterators

2. reverse iterators

3. stream iterators

function adapters

4. 用于函数指针：ptr_fun

5. 用于成员函数指针： mem_fun, mem_fun_ref

总结

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