STL source code analysis: conceptual understanding of iterators, and code testing.

目的：理解STL源码
The reason for iterators comes from a design pattern.它提供一个方法,Allow users to access the data one by one,Regardless of the structure of the data inside（树状,线性,数组,图等结构）.It's different from how access to data structures looks,It uniformly accesses complete data one by one.
在STLThe iterator can not only access the data in it one by one,It also acts as an adhesive,Separate data structures and algorithms.Data structures and algorithms are divided,Not only can it be easy to read and write code,At the same time, it conforms to the open-closed principle in development.If each data structure uses an algorithm,Algorithms can be developed elsewhere,Then use iterators to glue data structures and algorithms together.具体测试如下：数据结构有vector, list, deque三种;算法有find一种.findAlgorithms are applied to these three data structures.具体代码如下：

#include<vector>
#include<list>
#include<deque>
#include<algorithm>
#include<iostream>

using namespace std;

int main()
{
    
	const int arraysize = 7;
	int ia[arraysize] = {
    0,1,2,3,4,5,6};
	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(), 4);
	if(it1 == ivect.end())
	{
    
		cout<<"4 not found in ivect.. "<<std::endl;
	}
	else
	{
    
		cout << "4 found in ivect..."<<std::endl;
	}

	list<int>::iterator it2 = find(ilist.begin(), ilist.end(), 5);
	if(it2 == ilist.end())
	{
    
		cout << "5 not found in ilist... " << endl;
	}
	else
	{
    
		cout << "5 found in ilist... " << endl;
	}

	deque<int>::iterator it3 = find(ideque.begin(), ideque.end(), 6);
	if(it3 == ideque.end())
	{
    
		cout << "6 not found in ideque... " << endl;
	}
	else
	{
    
		cout << "6 found in ideque... " << endl;
	}

	return 0;
}

代码中,搜索功能的findapplied to three data structures,Its test results are as follows：

它能找到4,5,6.Search function applied,This is also a very important role of iterators.

感悟：STL的设计非常精巧,Iterators are also a very important part,Provide a trick for designing your own code in the future.In the future, try to separate the basic algorithm from the data structure,Then use iterators to realize the fusion of algorithms and data structures.