STL迭代器简介

标准模板库(The Standard Template Library, STL)定义了五种迭代器。下面的图表画出了这几种：

 

            input         output

              /            /

                 forward

                     |

                bidirectional

                     |

               random access

要注意，上面这图表并不是表明它们之间的继承关系：而只是描述了迭代器的种类和接口。处于图表下层的迭代器都是相对于处于图表上层迭代器的扩张集。例如：forward迭代器不但拥有input和output迭代器的所有功能，还拥有更多的功能。

   各个迭代器的功能如下：

迭代器类别	说明
输入	从容器中读取元素。输入迭代器只能一次读入一个元素向前移动，输入迭代器只支持一遍算法，同一个输入迭代器不能两遍遍历一个序列
输出	向容器中写入元素。输出迭代器只能一次一个元素向前移动。输出迭代器只支持一遍算法，统一输出迭代器不能两次遍历一个序列
正向	组合输入迭代器和输出迭代器的功能，并保留在容器中的位置
双向	组合正向迭代器和逆向迭代器的功能，支持多遍算法
随机访问	组合双向迭代器的功能与直接访问容器中任何元素的功能，即可向前向后跳过任意个元素

 

下表中，每种迭代器均可进行包括表中前一种迭代器可进行的操作。

所有迭代器：

p++	前置自增迭代器
++p	后置自增迭代器

输入迭代器：

*p	复引用迭代器，作为右值 注：此时以容器作为输入源，读容器
p=p1	将一个迭代器赋给另一个迭代器
p==p1	比较迭代器的相等性
p!=p1	比较迭代器的不等性

输出迭代器：

*p	复引用迭代器，作为左值 注：输出到容器，写容器
p=p1	将一个迭代器赋给另一个迭代器

正向迭代器：

提供输入输出迭代器的所有功能。

双向迭代器：

--p	前置自减迭代器
p--	后置自减迭代器

随机迭代器：

p+=i	将迭代器递增i位
p-=i	将迭代器递减i位
p+i	在p位加i位后的迭代器
p-i	在p位减i位后的迭代器
p[i]	返回p位元素偏离i位的元素引用
p<p1	如果迭代器p的位置在p1前，返回true，否则返回false
p<=p1	p的位置在p1的前面或同一位置时返回true，否则返回false
p>p1	如果迭代器p的位置在p1后，返回true，否则返回false
p>=p1	p的位置在p1的后面或同一位置时返回true，否则返回false

 

   下面列举了些例子说明各个容器的用法：
1、vector

#include <iostream> #include <vector> int main() { std::vector<char> charVector; int x; for (x=0; x<10; ++x) charVector.push_back(65 + x); int size = charVector.size(); for (x=0; x<size; ++x) { std::vector<char>::iterator start = charVector.begin(); charVector.erase(start); std::vector<char>::iterator iter; for (iter = charVector.begin(); iter != charVector.end(); iter++) { std::cout << *iter; } std::cout << std::endl; } return 0; }

2、deque

#include <iostream> #include <deque> int main() { std::deque<char> charDeque; int x; for (x=0; x<10; ++x) charDeque.push_front(65 + x); int size = charDeque.size(); for (x=0; x<size; ++x) { std::deque<char>::iterator start = charDeque.begin(); charDeque.erase(start); std::deque<char>::iterator iter; for (iter = charDeque.begin(); iter != charDeque.end(); iter++) { std::cout << *iter; } std::cout << std::endl; } return 0; }

3、list

#include <iostream> #include <list> int main() { // Create and populate the list. int x; std::list<char> charList; for (x=0; x<10; ++x) charList.push_front(65 + x); // Display contents of list. std::cout << "Original list: "; std::list<char>::iterator iter; for (iter = charList.begin(); iter != charList.end(); iter++) { std::cout << *iter; //char ch = *iter; //std::cout << ch; } std::cout << std::endl; // Insert five Xs into the list. std::list<char>::iterator start = charList.begin(); charList.insert(++start, 5, 'X'); // Display the result. std::cout << "Resultant list: "; for (iter = charList.begin(); iter != charList.end(); iter++) { std::cout << *iter; //char ch = *iter; //std::cout << ch; } return 0; }

4、set

#include <iostream> #include <set> int main() { // Create the set object. std::set<char> charSet; // Populate the set with values. charSet.insert('E'); charSet.insert('D'); charSet.insert('C'); charSet.insert('B'); charSet.insert('A'); // Display the contents of the set. std::cout << "Contents of set: " << std::endl; std::set<char>::iterator iter; for (iter = charSet.begin(); iter != charSet.end(); iter++) std::cout << *iter << std::endl; std::cout << std::endl; // Find the D. iter = charSet.find('D'); if (iter == charSet.end()) std::cout << "Element not found."; else std::cout << "Element found: " << *iter; return 0; }

5、multiset

#include <iostream> #include <set> int main() { // Create the first set object. std::multiset<char> charMultiset1; // Populate the multiset with values. charMultiset1.insert('E'); charMultiset1.insert('D'); charMultiset1.insert('C'); charMultiset1.insert('B'); charMultiset1.insert('A'); charMultiset1.insert('B'); charMultiset1.insert('D'); // Display the contents of the first multiset. std::cout << "Contents of first multiset: " << std::endl; std::multiset<char>::iterator iter; for (iter = charMultiset1.begin(); iter != charMultiset1.end(); iter++) std::cout << *iter << std::endl; std::cout << std::endl; // Create the second multiset object. std::multiset<char> charMultiset2; // Populate the multiset with values. charMultiset2.insert('J'); charMultiset2.insert('I'); charMultiset2.insert('H'); charMultiset2.insert('G'); charMultiset2.insert('F'); charMultiset2.insert('G'); charMultiset2.insert('I'); // Display the contents of the second multiset. std::cout << "Contents of second multiset: " << std::endl; for (iter = charMultiset2.begin(); iter != charMultiset2.end(); iter++) std::cout << *iter << std::endl; std::cout << std::endl; // Compare the sets. if (charMultiset1 == charMultiset2) std::cout << "set1 == set2"; else if (charMultiset1 < charMultiset2) std::cout << "set1 < set2"; else if (charMultiset1 > charMultiset2) std::cout << "set1 > set2"; return 0; }

6、map

#include <iostream> #include <map> typedef std::map<int, char> MYMAP; int main() { // Create the first map object. MYMAP charMap1; // Populate the first map with values. charMap1[1] = 'A'; charMap1[4] = 'D'; charMap1[2] = 'B'; charMap1[5] = 'E'; charMap1[3] = 'C'; // Display the contents of the first map. std::cout << "Contents of first map: " << std::endl; MYMAP::iterator iter; for (iter = charMap1.begin(); iter != charMap1.end(); iter++) { std::cout << (*iter).first << " --> "; std::cout << (*iter).second << std::endl; } std::cout << std::endl; // Create the second map object. MYMAP charMap2; // Populate the first map with values. charMap2[1] = 'F'; charMap2[4] = 'I'; charMap2[2] = 'G'; charMap2[5] = 'J'; charMap2[3] = 'H'; // Display the contents of the second map. std::cout << "Contents of second map: " << std::endl; for (iter = charMap2.begin(); iter != charMap2.end(); iter++) { std::cout << (*iter).first << " --> "; std::cout << (*iter).second << std::endl; } std::cout << std::endl; // Compare the maps. if (charMap1 == charMap2) std::cout << "map1 == map2"; else if (charMap1 < charMap2) std::cout << "map1 < map2"; else if (charMap1 > charMap2) std::cout << "map1 > map2"; return 0; }

7、multimap

#include <iostream> #include <map> typedef std::multimap<int, char> MYMAP; int main() { // Create the first multimap object. MYMAP charMultimap; // Populate the multimap with values. charMultimap.insert(MYMAP::value_type(1,'A')); charMultimap.insert(MYMAP::value_type(4,'C')); charMultimap.insert(MYMAP::value_type(2,'B')); charMultimap.insert(MYMAP::value_type(7,'E')); charMultimap.insert(MYMAP::value_type(5,'D')); charMultimap.insert(MYMAP::value_type(3,'B')); charMultimap.insert(MYMAP::value_type(6,'D')); // Display the contents of the first multimap. std::cout << "Contents of first multimap: " << std::endl; MYMAP::iterator iter; for (iter = charMultimap.begin(); iter != charMultimap.end(); iter++) { std::cout << (*iter).first << " --> "; std::cout << (*iter).second << std::endl; } std::cout << std::endl; // Create the second multimap object. MYMAP charMultimap2; // Populate the second multimap with values. charMultimap2.insert(MYMAP::value_type(1,'C')); charMultimap2.insert(MYMAP::value_type(4,'F')); charMultimap2.insert(MYMAP::value_type(2,'D')); charMultimap2.insert(MYMAP::value_type(7,'E')); charMultimap2.insert(MYMAP::value_type(5,'F')); charMultimap2.insert(MYMAP::value_type(3,'E')); charMultimap2.insert(MYMAP::value_type(6,'G')); // Display the contents of the second multimap. std::cout << "Contents of second multimap: " << std::endl; for (iter = charMultimap2.begin(); iter != charMultimap2.end(); iter++) { std::cout << (*iter).first << " --> "; std::cout << (*iter).second << std::endl; } std::cout << std::endl; // Compare the multimaps. if (charMultimap == charMultimap2) std::cout << "multimap1 == multimap2"; else if (charMultimap < charMultimap2) std::cout << "multimap1 < multimap2"; else if (charMultimap > charMultimap2) std::cout << "multimap1 > multimap2"; return 0; }

8、stack

#include <iostream> #include <list> #include <stack> int main() { std::stack<int, std::list<int> > intStack; int x; std::cout << "Values pushed onto stack:" << std::endl; for (x=1; x<11; ++x) { intStack.push(x*100); std::cout << x*100 << std::endl; } std::cout << "Values popped from stack:" << std::endl; int size = intStack.size(); for (x=0; x<size; ++x) { std::cout << intStack.top() << std::endl; intStack.pop(); } return 0; } 9、queue #include <iostream> #include <list> #include <queue> int main() { std::queue<int, std::list<int> > intQueue; int x; std::cout << "Values pushed onto queue:" << std::endl; for (x=1; x<11; ++x) { intQueue.push(x*100); std::cout << x*100 << std::endl; } std::cout << "Values removed from queue:" << std::endl; int size = intQueue.size(); for (x=0; x<size; ++x) { std::cout << intQueue.front() << std::endl; intQueue.pop(); } return 0; }

9、queue

#include <iostream> #include <list> #include <queue> int main() { std::queue<int, std::list<int> > intQueue; int x; std::cout << "Values pushed onto queue:" << std::endl; for (x=1; x<11; ++x) { intQueue.push(x*100); std::cout << x*100 << std::endl; } std::cout << "Values removed from queue:" << std::endl; int size = intQueue.size(); for (x=0; x<size; ++x) { std::cout << intQueue.front() << std::endl; intQueue.pop(); } return 0; }

10、priority_queue

#include <iostream> #include <list> #include <queue> int main() { std::priority_queue<int, std::vector<int>,std::greater<int> > intPQueue; int x; intPQueue.push(400); intPQueue.push(100); intPQueue.push(500); intPQueue.push(300); intPQueue.push(200); std::cout << "Values removed from priority queue:" << std::endl; int size = intPQueue.size(); for (x=0; x<size; ++x) { std::cout << intPQueue.top() << std::endl; intPQueue.pop(); } return 0; }

map、set 和 list 类型提供双向迭代器，而 string、vector 和 deque 容器上定义的迭代器都是随机访问迭代器都是随机访问迭代器，用作访问内置数组元素的指针也是随机访问迭代器。istream_iterator 是输入迭代器，而 ostream_iterator 则是输出迭代器。

   更多迭代器介绍可参考《C++ Primer》11.3节。

 

   转载：http://blog.youkuaiyun.com/weide001/archive/2009/07/03/4319212.aspx