Iterator 设计思维
STL 中 container 和 algorithm 是相对独立的，本身设计也是泛型化的。Iterator 就是用来将这两者联系在一起的。
Iterator 是一种 smart pointer
可以不用 delete
Iterator 属性
iterator_traits 是用来抽取 iterator 中的类型(特指 value type)的。
这是 iterator 中常见的五种属性。
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| template <class I>
struct iterator_traits
{
typedef typename I::iterator_category iterator_category; //category
typedef typename I::value_type value_type; // type
typedef typename I::difference_type difference_type; //
typedef typename I::pointer pointer; // T*
typedef typename I::reference reference; // T&
};
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| #include <iostream> // std::cout
#include <iterator> // std::iterator_traits
#include <typeinfo> // typeid
using namespace std;
int main() {
typedef std::iterator_traits<double*> traits;
cout << typeid(traits::iterator_category).name() << endl;
cout << typeid(traits::value_type).name() << endl;
cout << typeid(traits::difference_type).name() << endl;
cout << typeid(traits::pointer).name() << endl;
cout << typeid(traits::reference).name() << endl;
return 0;
}
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| NSt3__126random_access_iterator_tagE
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yanghaoli
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iterator_category
- Input iterator: Read only. Cannot be change.
- Output iterator: Write only.
- Forward iterator: Allow write and only one direction.(only operator++). Some algorithms use one direction enough.(like replace())
- Bidirectional iterator: For some algorithm will move both direction. Support operator++ and operator–.
- Random access iterator: Support more operator. p+n, p-n, p[n], p1-p2, p1 < p2.
iterator & const_iterator
const_iterator is read only.
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| #include <iostream>
#include <vector>
using namespace std;
int main(int argc, char const *argv[])
{
vector<int> iv = {1,2,3,4,5};
vector<int>::iterator a = iv.begin();
vector<int>::const_iterator b = iv.begin();
*a = 12;
cout << *a << endl;
// *b = 100; // NOT WORK
cout << *b << endl;
}
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