Iterators

Any of those iterators that satisfy the requirements of output iterators are sometimes referred to as mutable iterators, while those that don’t are referred to as constant iterators.

C++17 adds a sixth kind of iterator, the Contiguous Iterator.

• It provides some optimisations above random access iterators in the case where the container elements are stored contiguously.

We will see later that iterators LegacyIterators from C++20.

Reverse iterators

Use rbegin() and rend().

#include <iostream>
#include <vector>
using namespace std;

int main()
{
vector<char> c;
c.push_back('A');
c.push_back('B');
c.push_back('C');
cout << "Forward:\n";
vector<char>::iterator p;
for (p=c.begin(); p!=c.end(); p++) cout<< *p << " ";
cout << endl;
cout << "Reverse:\n";
vector<char>::reverse_iterator rp;
for(rp=c.rbegin(); rp!=c.rend(); rp++) cout<< *rp <<" ";
cout << endl;
return 0;
}

Stream iterators

Two useful stream iterators

istream_iterator<type> isIterator(istream&);
ostream_iterator<type> osIterator(ostream&);
ostream_iterator<type> osIterator(ostream&, char* deLimit);

int main()
{
vector<int> x;
copy(istream_iterator<int>(cin), istream_iterator(), back_inserter(x));
vector<int>::iterator p = remove_if(x.begin(), x.end(), is_even);
x.erase(p, x.end());
copy(x.begin(), x.end(), ostream_iterator<int>(cout, "\n "));
}

int main()
{
double value1, value2;
cout << "Please, insert two values: ";
istream_iterator<double> eos; // end-of-stream iterator
istream_iterator<double> iit (std::cin); // stdin iterator
if (iit!=eos)
value1 = *iit;
++iit;
if (iit!=eos)
value2 = *iit;
cout << value1 << "*" << value2 << "=" << (value1*value2) << '\n';
}