Detailed explanation of standard library insertion iterator
Insert iterator function: functions such as copy can't change the size of the container, so sometimes the container is empty before copy. If you don't use insert iterator, you can't use functions such as copy.
For example, the following code is wrong:
list<int> lst{1,2,3,4};
list<int> lst2,lst3;
copy(lst.cbegin(), lst.cend(), lst2.begin());Lst2 is an empty container. The copy function cannot expand container lst2, so a runtime error will occur.
Using insert iterator can solve the above problems well
list<int> lst{1,2,3,4};
list<int> lst2,lst3;
copy(lst.cbegin(), lst.cend(), inserter(lst3, lst3.begin()));Three kinds of insertion iterators
| iterator | Function description |
|---|---|
| back_inserter | Create an iterator using push back |
| front_inserter | Create an iterator using push front |
| inserter | Create an iterator that uses insert before the element is inserted into the specified location |
What's special about inserter:
//Suppose it is an iterator generated by an inserter *it = val；//The effect is the same as the following two lines of code it = c.insert(it, val);//it points to the newly added element ++it;//Increment it so that it points to the original element
Example:
#include <iostream>
#include <vector>
#include <list>
#include <algorithm>
using namespace std;
int main(){
//The copy function does not change the size of the container, but with the insert iterator,
//It will change the size of the container
/*
list<int> lst{1,2,3,4};
list<int> lst2,lst3;
//Run error, because lst2 is an empty list, the copy function does not increase the size of the container
//copy(lst.cbegin(), lst.cend(), lst2.begin());
//Results: 4,3,2,1
copy(lst.cbegin(), lst.cend(), front_inserter(lst2));
//Results: 1,2,3,4
copy(lst.cbegin(), lst.cend(), inserter(lst3, lst3.begin()));
for(auto const &s : lst2){
cout << s << " ";
}
cout << endl;
for(auto const &s : lst3){
cout << s << " ";
}
cout << endl;
*/
//Unique? Copy duplicate elements to a new container
vector<int> ivec{1,2,1,2,3,4,3,3,3,2,2,1,1,1};
list<int> lst;
sort(ivec.begin(),ivec.end());
unique_copy(ivec.cbegin(), ivec.cend(),back_inserter(lst));
for(auto const &s : lst){
cout << s << " ";
}
cout << endl;
}