Iterator 学习之迭代器函数操作

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本篇学习Iterator的迭代器函数操作，具体函数如下：

定义于头文件 `<iterator>`
advance	令迭代器前进给定的距离 (函数模板)
distance	返回两个迭代器间的距离 (函数模板)
begin	开始迭代器 (函数模板)
end	结束迭代器 (函数模板)
next (C++11)	令迭代器自增 (函数模板)
prev (C++11)	令迭代器自减 (函数模板)

代码示例1

advance我们知道list列表可以取头元素和尾元素，那如果要取中间元如果操作呢，因为它没有[i]也有没at(i)操作，那么使用advance函数就可以取到中间的任意元素，具体示例如下：

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#include <iostream>
#include <iterator>
#include <list>

using namespace std;

int main()
{
    list<int> mylist{10,20,30,40,50,60,70,80,90,100};
    for(auto li = mylist.begin(); li != mylist.end(); ++li)
    {
        cout << *li << "t";
    }
    cout << "n";
    //取第5个无素
    list<int>::iterator it = mylist.begin();
    std::advance(it, 4);
    cout << "The five element in mylist is: " << *it << endl;

    list<int>::iterator it1 = mylist.begin();
    std::advance(it1, 6);
    cout << "The seven element in mylist is: " << *it1 << endl;
    *it1 = 90;
    for(auto li = mylist.begin(); li != mylist.end(); ++li)
    {
        cout << *li << "t";
    }
    cout << "n";
    cout << "Hello World!" << endl;
    return 0;
}

代码示例2 distance取两个迭代器之间的距离

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#include <iostream>
#include <iterator>
#include <vector>

using namespace std;

int main()
{
    list<int> mylist{10,20,30,40,50,60,70,80,90,100};
    std::list<int>::iterator first = mylist.begin();
    std::list<int>::iterator last = mylist.end();
    std::cout << "list   distance(first, last) = " << std::distance(first, last) << 'n';
    //std::cout << "list   distance(last, first) = " << std::distance(last, first) << 'n'; //list不能使用
    std::vector<int> vec{32, 15, 43, 25, 36};

    std::vector<int>::iterator vfirst = vec.begin();
    std::vector<int>::iterator vlast = vec.end();
    std::cout << "vector distance(first, last) = " << std::distance(vfirst, vlast) << 'n';
    std::cout << "vector distance(last, first) = " << std::distance(vlast, vfirst) << 'n';

    cout << "n";
    cout << "Hello World!" << endl;
    return 0;
}

代码示例3 begin开始迭代器

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#include <iostream>
#include <iterator>
#include <vector>

using namespace std;

int main()
{
    //3.begin
    std::vector<int> vec{32, 15, 43, 25, 36};
    std::vector<int>::iterator iter2 = vec.begin();
    //取vector第2个元素
    ++iter2;
    std::cout << "vector iter2 = " << *iter2 << 'n';

    cout << "Hello World!" << endl;
    return 0;
}

代码示例4 end结束迭代器

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#include <iostream>
#include <iterator>
#include <vector>

using namespace std;

int main()
{
    std::vector<int> vec{32, 15, 43, 25, 36};
    //取vector最后一个元素
    std::vector<int>::iterator iter = vec.begin();
    while(iter != vec.end())
    {
        ++iter;
        if(iter == vec.end())
        {
            //取最后一个元素
            --iter;
            std::cout << "vector iter = " << *iter << 'n';
            break;
        }
    }


    cout << "n";
    cout << "Hello World!" << endl;
    return 0;
}