ITERATOR 迭代器
template<class InputIterator,class T>
InputIterator find(InputIterator first,InputIterator last,const T& value)
{
while(first != last && *first != value)
++first;
return first;
}
代码示例
#include <iostream>
#include <vector>
#include <list>
#include <deque>
#include <algorithm>
#include <iostream> using namespace std; int main(int argc, char *argv[])
{
const int arraySize = ;
int ia[arraySize] = {,,,,,,}; vector<int> ivect(ia,ia+arraySize);
list<int> ilist(ia,ia+arraySize);
deque<int> ideque(ia,ia+arraySize); vector<int>::iterator it1 = find(ivect.begin(),ivect.end(),);
if(it1 == ivect.end())
cout << "4 not found." << endl;
else
cout << "4 found. " << * it1 << endl; list<int>::iterator it2 = find(ilist.begin(),ilist.end(),);
if(it2 == ilist.end())
cout << "6 not found. " << endl;
else
cout << "6 found. " << *it2 << endl; deque<int>::iterator it3 = find(ideque.begin(),ideque.end(),);
if(it3 == ideque.end())
cout << "8 not found. " << endl;
else
cout << "8 find " << *it3 << endl; return ;
}
stl中容器有vector\set\list等等等等
算法有find\count等
两者独立 而他们之间的联系便是由iterator进行连接 将两者粘合起来
iterator类似智能指针
智能指针auto_ptr 除了拥有平常指针概念的功能 还具有引用计数功能
通过对该指针指向的元素的引用计数 自动释放元素内存资源 而不必手动调用delete
(auto_ptr 在c++11之后已经被智能指针shared_ptr unique_ptr取代)
示例代码如下
#include <iostream>
#include <vector>
#include <list>
#include <deque>
#include <algorithm>
#include <iostream> using namespace std; template<class T>
class auto_ptr{
public:
explicit auto_ptr(T* p = 0):pointer(p){}
template<typename U>
auto_ptr(auto_ptr<U>& rhs):pointer(rhs.release()){}
~auto_ptr(){ cout << "enter delete status\n";delete pointer;} template<class U>
auto_ptr<T>& operator=(auto_ptr<U>& rhs){
if(this != &rhs) reset(rhs.release());
return *this;
}
T& operator*()const{return *pointer;}
T* operator->()const{return pointer;}
T* get()const{return pointer;} private:
T* pointer;
}; int main(int argc, char *argv[])
{
auto_ptr<string> ps(new string("test"));
cout << *ps << endl;
cout << ps->size() << endl;
return 0;
}
要使用iterator这个智能指针 就需要识别指向的元素的相关信息，比如类别、引用等
代码使用了trait技巧将元素信息提取出来
#include <iostream>
#include <vector>
#include <list>
#include <deque>
#include <algorithm>
#include <iostream>
#include <typeinfo> using namespace std; struct INT{
typedef int value_type;
typedef int difference_type;
typedef int* pointer;
typedef int& reference;
}; struct FLOAT{
typedef float value_type;
typedef float difference_type;
typedef float* pointer;
typedef float& reference;
}; template<class I>
struct Iterator_Traits{
//typedef typename I::iterator_category iterator_category;
typedef typename I::value_type value_type;
typedef typename I::difference_type difference_type;
typedef typename I::pointer pointer;
typedef typename I::reference reference;
}; int main(int argc, char *argv[])
{
std::cout << typeid(Iterator_Traits<INT>::reference).name() << std::endl;
std::cout << typeid(Iterator_Traits<FLOAT>::reference).name() << std::endl; return 0;
}
至此 除了
//typedef typename I::iterator_category iterator_category;
还没解决 其他都解决完毕
iterator_category是什么东西呢？
iterator迭代器也是有类型区分的
那么在实际代码中是如何进行识别呢？
在代码执行时才识别区分 效率太低
#include <iostream>
#include <vector>
#include <list>
#include <deque>
#include <algorithm>
#include <iostream>
#include <typeinfo> using namespace std; //申请五个作为迭代器iterator类别的结构
struct input_iterator_tag_{};
struct output_iterator_tag_{};
struct forward_iterator_tag_:public input_iterator_tag_{};
struct bidirectional_iterator_tag_:public forward_iterator_tag_{};
struct random_access_iterator_tag_:public bidirectional_iterator_tag_{}; struct INT{
typedef input_iterator_tag_ iterator_category;
typedef int value_type;
typedef int difference_type;
typedef int* pointer;
typedef int& reference;
}; struct FLOAT{
typedef output_iterator_tag_ iterator_category;
typedef float value_type;
typedef float difference_type;
typedef float* pointer;
typedef float& reference;
}; template<class I>
struct MyIterator_Traits{
typedef typename I::iterator_category iterator_category;
typedef typename I::value_type value_type;
typedef typename I::difference_type difference_type;
typedef typename I::pointer pointer;
typedef typename I::reference reference;
};
template<typename T,typename Distance>
void test(T t,Distance n){
typename MyIterator_Traits<T>::iterator_category SELECT_TYPE;
test_(t,n,SELECT_TYPE);
} template<typename InputIterator,typename Distance>
void test_(InputIterator i,Distance j,input_iterator_tag_){
cout << "input_iterator_tag_" << endl;
} template<typename InputIterator,typename Distance>
void test_(InputIterator i,Distance j,output_iterator_tag_){
cout << "output_iterator_tag_" << endl;
} int main(int argc, char *argv[])
{
INT i;
FLOAT f;
char c;
test(i,c);
test(f,c); return 0;
}
我们对不同的迭代器 指定不同的tag 这样就会进入到不同的函数中去了