c/c++ 標準庫 迭代器
begin和end運算子返回的具體型別由物件是否是常量決定，如果物件是常量，begin和end返回const_iterator；如果物件不是常量，返回iteraotor
1，但凡是使用了迭代器的迴圈體，都不要向迭代器所屬的容器新增元素。
2，不能在範圍for迴圈中向vector物件新增元素
標準庫 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 不可改變vector::const_iterator型別
/*
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是可改變的vector::iterator，所以編譯錯誤
for(auto s : v){
cout << s;
}
cout << endl;
*/
//test4 不可改變string::const_iterator型別
/*
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型別的iterator
/*
string s1("aaaa");
auto it1 = s1.cbegin();
//*it1 = `c`;//不可以通過const型別的iterator改變原來的物件
cout << s1 << endl;
vector<int> v(4,2);
auto vit1 = v.cbegin();
//*vit1 = 5;//不可以通過const型別的iterator改變原來的物件
*/
//test6 string迭代器運算
/*
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迭代器運算
/*
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 利用迭代器實現二分法
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;
else
beg = mid + 1;
mid = beg + (end - beg) / 2;
}
if(mid == end){
cout << "not found" << endl;
}
else{
idx = mid - v.begin();
cout << idx << ":" << *mid << endl;
}
}