Editing Iterator pattern (section)

== Example ==
{{main|Iterator}}
Some languages standardize syntax. C++ and Python are notable examples.
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=== C++ ===
[[C++]] implements iterators with the semantics of [[pointer (computer programming)|pointer]]s in that language. In C++, a class can overload all of the pointer operations, so an iterator can be implemented that acts more or less like a pointer, complete with dereference, increment, and decrement. This has the advantage that C++ algorithms such as <code>std::sort</code> can immediately be applied to plain old memory buffers, and that there is no new syntax to learn. However, it requires an "end" iterator to test for equality, rather than allowing an iterator to know that it has reached the end. In C++ language, we say that an iterator models the iterator [[concept (generic programming)|concept]].

This C++11 implementation is based on chapter "Generalizing vector yet again".<ref>{{cite book |author=Bjarne Stroustrup |title=Programming: Principles and Practice using C++ |edition=2 |publisher=Addison Wesley |year=2014 |isbn=978-0-321-99278-9 |pages=729 ff.}}</ref>

<syntaxhighlight lang="c++">
#include <iostream>
#include <stdexcept>
#include <initializer_list>
		
class Vector {
public:
  using iterator = double*;
  iterator begin() { return elem; }
  iterator end() { return elem + sz; }
  
  Vector(std::initializer_list<double> lst) :elem(nullptr), sz(0) {
    sz = lst.size();
    elem = new double[sz];
    double* p = elem;
    for (auto i = lst.begin(); i != lst.end(); ++i, ++p) {
      *p = *i;
    }
  }  
  ~Vector() { delete[] elem; }
  int size() const { return sz; }
  double& operator[](int n) {
    if (n < 0 || n >= sz) throw std::out_of_range("Vector::operator[]");
    return elem[n];
  }
  Vector(const Vector&) = delete; // rule of three
  Vector& operator=(const Vector&) = delete;
private:
  double* elem;
  int sz;
};

int main() {
  Vector v = {1.1*1.1, 2.2*2.2};
  
  for (const auto& x : v) {
    std::cout << x << '\n';
  }
  for (auto i = v.begin(); i != v.end(); ++i) {
    std::cout << *i << '\n';
  }
  for (auto i = 0; i <= v.size(); ++i) {
    std::cout << v[i] << '\n';
  } 
}
</syntaxhighlight>

The program output is

<syntaxhighlight lang="c++">
1.21
4.84
1.21
4.84
1.21
4.84
terminate called after throwing an instance of 'std::out_of_range'
  what():  Vector::operator[]
</syntaxhighlight>