c/c++ 标准库 迭代器
begin和end运算符返回的具体类型由对象是否是常量决定，如果对象是常量，begin和end返回const_iterator；如果对象不是常量，返回iteraotor
1，但凡是使用了迭代器的循环体，都不要向迭代器所属的容器添加元素。
2，不能在范围for循环中向vector对象添加元素
标准库 迭代器(iterator)的小例子
test1~test8
#include <iostream>
#include <string>
#include <vector>using namespace std;int main(){//test1 /* string s("abc bdc"); auto it = s.begin(); while(it != s.end()){ *it = toupper(*it); ++it; } cout << s << endl; *///test2 /* string s("abd ddd"); for(auto it = s.begin(); it != s.end() && !isspace(*it); ++it){ *it = toupper(*it); } cout << s << endl; *///test3 不可改变vector::const_iterator类型 /* vector<int>:: iterator it; vector<int>:: const_iterator it2; vector<int> v(5,1); it = v.begin(); it2 = v.begin(); vector<int> const cv(5,2); //it = cv.begin();//it是可改变的vector::iterator，所以编译错误 for(auto s : v){ cout << s; } cout << endl; *///test4 不可改变string::const_iterator类型 /* string::iterator sit; string::const_iterator sit2; string s1("abc"); sit2 = s1.begin(); while(sit2 != s1.end()){ //*sit2 = toupper(*sit2); cout << *sit2; ++sit2; } cout << endl; *///test5 cbegin和cend,返回const类型的iterator /* string s1("aaaa"); auto it1 = s1.cbegin(); //*it1 = 'c';//不可以通过const类型的iterator改变原来的对象 cout << s1 << endl; vector<int> v(4,2); auto vit1 = v.cbegin(); //*vit1 = 5;//不可以通过const类型的iterator改变原来的对象 *///test6 string迭代器运算 /* string s("abcd"); string s1("abc"); vector<int> v(5,3); auto it1 = s.begin(); auto it2 = s.begin(); if(it1 == it2){ cout << "=" << endl; } ++it1; it1 += 1; if(it1 > it2){ cout << ">" << endl; cout << it1 - it2 << endl; } string::difference_type juli = it1 - it2; cout << juli << endl; *///test7 vector迭代器运算 /* vector<string> s(4,"abcd"); vector<string> s1(5,"abc"); auto it1 = s.begin(); auto it2 = s.begin(); if(it1 == it2){ cout << "=" << endl; } ++it1; it1 += 1; if(it1 > it2){ cout << ">" << endl; cout << it1 - it2 << endl; } vector<string>::difference_type juli = it1 - it2; cout << juli << endl; *///test8 利用迭代器实现二分法 vector<string> v{"a","b","c","d","e"};string target("b");vector<string>::size_type idx = 0;auto beg = v.begin();auto mid = v.begin() + v.size() / 2;auto end = v.end();while(mid != end && *mid != target){if(target < *mid)end = mid;elsebeg = mid + 1;mid = beg + (end - beg) / 2;}if(mid == end){cout << "not found" << endl;}else{idx = mid - v.begin();cout << idx << ":" << *mid << endl;}
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