STL-compatible iterators for custom containers [closed] - c++

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I have a custom container that I have been using for many years without issues. Recently I found out that if I define iterators for my container, I can effectively use all of the algorithms defined in <algorithm>. Not only that, it seems that thrust library (basically think CUDA version of STL for Nvidia GPUs) heavily uses iterators and I am hoping that by using them I'll be able to use that library as well.
Anyway, since this is my first try at writing my own iterators, I thought I post what I have here to ask for further assistance and make sure what I'm doing is right. So, I wrote a little array class that supports both iterator and const_iterator classes. I ran my class with a bunch of different STL algorithms and all seem to work fine but that does not necessarily mean I've got everything right! In particular, is there any operator that I miss for my iterators?
Have I defined extra unnecessary ones? Also, since most of iterator and const_iterator look similar, is there a way to prevent duplication?
I'm open to suggestions and improvements :)
Live example: http://ideone.com/7YdiQY
#include <cstddef>
#include <iostream>
#include <iterator>
#include <algorithm>
template<typename T>
class my_array{
T* data_;
std::size_t size_;
public:
// ---------------------------------
// Forward declaration
// ---------------------------------
class const_iterator;
// ---------------------------------
// iterator class
// ---------------------------------
class iterator: public std::iterator<std::random_access_iterator_tag, T>
{
public:
iterator(): p_(NULL) {}
iterator(T* p): p_(p) {}
iterator(const iterator& other): p_(other.p_) {}
const iterator& operator=(const iterator& other) {p_ = other.p_; return other;}
iterator& operator++() {p_++; return *this;} // prefix++
iterator operator++(int) {iterator tmp(*this); ++(*this); return tmp;} // postfix++
iterator& operator--() {p_--; return *this;} // prefix--
iterator operator--(int) {iterator tmp(*this); --(*this); return tmp;} // postfix--
void operator+=(const std::size_t& n) {p_ += n;}
void operator+=(const iterator& other) {p_ += other.p_;}
iterator operator+ (const std::size_t& n) {iterator tmp(*this); tmp += n; return tmp;}
iterator operator+ (const iterator& other) {iterator tmp(*this); tmp += other; return tmp;}
void operator-=(const std::size_t& n) {p_ -= n;}
void operator-=(const iterator& other) {p_ -= other.p_;}
iterator operator- (const std::size_t& n) {iterator tmp(*this); tmp -= n; return tmp;}
std::size_t operator- (const iterator& other) {return p_ - other.p_;}
bool operator< (const iterator& other) {return (p_-other.p_)< 0;}
bool operator<=(const iterator& other) {return (p_-other.p_)<=0;}
bool operator> (const iterator& other) {return (p_-other.p_)> 0;}
bool operator>=(const iterator& other) {return (p_-other.p_)>=0;}
bool operator==(const iterator& other) {return p_ == other.p_; }
bool operator!=(const iterator& other) {return p_ != other.p_; }
T& operator[](const int& n) {return *(p_+n);}
T& operator*() {return *p_;}
T* operator->(){return p_;}
private:
T* p_;
friend class const_iterator;
};
// ---------------------------------
// const_iterator class
// ---------------------------------
class const_iterator: public std::iterator<std::random_access_iterator_tag, T>
{
public:
const_iterator(): p_(NULL) {}
const_iterator(const T* p): p_(p) {}
const_iterator(const iterator& other): p_(other.p_) {}
const_iterator(const const_iterator& other): p_(other.p_) {}
const const_iterator& operator=(const const_iterator& other) {p_ = other.p_; return other;}
const const_iterator& operator=(const iterator& other) {p_ = other.p_; return other;}
const_iterator& operator++() {p_++; return *this;} // prefix++
const_iterator operator++(int) {const_iterator tmp(*this); ++(*this); return tmp;} // postfix++
const_iterator& operator--() {p_--; return *this;} // prefix--
const_iterator operator--(int) {const_iterator tmp(*this); --(*this); return tmp;} // postfix--
void operator+=(const std::size_t& n) {p_ += n;}
void operator+=(const const_iterator& other) {p_ += other.p_;}
const_iterator operator+ (const std::size_t& n) const {const_iterator tmp(*this); tmp += n; return tmp;}
const_iterator operator+ (const const_iterator& other) const {const_iterator tmp(*this); tmp += other; return tmp;}
void operator-=(const std::size_t& n) {p_ -= n;}
void operator-=(const const_iterator& other) {p_ -= other.p_;}
const_iterator operator- (const std::size_t& n) const {const_iterator tmp(*this); tmp -= n; return tmp;}
std::size_t operator- (const const_iterator& other) const {return p_ - other.p_;}
bool operator< (const const_iterator& other) const {return (p_-other.p_)< 0;}
bool operator<=(const const_iterator& other) const {return (p_-other.p_)<=0;}
bool operator> (const const_iterator& other) const {return (p_-other.p_)> 0;}
bool operator>=(const const_iterator& other) const {return (p_-other.p_)>=0;}
bool operator==(const const_iterator& other) const {return p_ == other.p_; }
bool operator!=(const const_iterator& other) const {return p_ != other.p_; }
const T& operator[](const int& n) const {return *(p_+n);}
const T& operator*() const {return *p_;}
const T* operator->() const {return p_;}
private:
const T* p_;
};
my_array()
: data_(NULL), size_(0)
{}
my_array(std::size_t size)
: data_(new T[size]), size_(size)
{}
my_array(const my_array<T>& other){
size_ = other.size_;
data_ = new T[size_];
for (std::size_t i = 0; i<size_; i++)
data_[i] = other.data_[i];
}
my_array(const const_iterator& first, const const_iterator& last){
size_ = last - first;
data_ = new T[size_];
for (std::size_t i = 0; i<size_; i++)
data_[i] = first[i];
}
~my_array(){
delete [] data_;
}
const my_array<T>& operator=(const my_array<T>& other){
size_ = other.size_;
data_ = new T[size_];
for (std::size_t i = 0; i<size_; i++)
data_[i] = other.data_[i];
return other;
}
const T& operator[](std::size_t idx) const {return data_[idx];}
T& operator[](std::size_t& idx) {return data_[idx];}
std::size_t size(){return size_;}
iterator begin(){ return iterator(data_); }
iterator end() { return iterator(data_+size_); }
const_iterator begin() const{ return const_iterator(data_); }
const_iterator end() const { return const_iterator(data_+size_);}
};
template<typename T>
void print(T t) {
std::cout << t << std::endl;
}
int main(){
// works!
int list [] = {1, 3, 5, 2, 4, 3, 5, 10, 10};
my_array<int> a(list, list+sizeof(list)/sizeof(int));
// works!
for (my_array<int>::const_iterator it = a.begin(), end = a.end();
it != end; ++it)
std::cout << ' ' << *it;
std::cout << std::endl;
// works!
std::for_each(a.begin(), a.end(), print<int>);
std::cout << std::endl;
// works!
my_array<int> b(a.size());
std::copy(a.begin(), a.end(), b.begin());
// works!
my_array<int>::iterator end = std::remove(a.begin(), a.end(), 5);
std::for_each(a.begin(), end, print<int>);
std::cout << std::endl;
// works!
std::random_shuffle(a.begin(), end);
std::for_each(a.begin(), end, print<int>);
std::cout << std::endl;
// works!
std::cout << "Counts of 3 in array = " << std::count(a.begin(), end, 3) << std::endl << std::endl;
// works!
std::sort(a.begin(), end);
std::for_each(a.begin(), end, print<int>);
std::cout << std::endl;
// works!
if (!std::binary_search(a.begin(), a.end(), 5))
std::cout << "Removed!" << std::endl;
return 0;
}

Answer 1

boost iterator provides a framework to create stl-compliant iterators and to adapt existing ones.
It allows you to focus on the functionality and generates all necessary traits, typedefs for you.
iterator and const_iterator creation without much code-duplication is supported as well.

Answer 2

The Boost iterator_adaptor can greatly simplify your code. The documentation has e.g. this example for a linked list iterator
template <class Value>
class node_iter
: public boost::iterator_adaptor<
node_iter<Value> // Derived
, Value* // Base
, boost::use_default // Value
, boost::forward_traversal_tag // CategoryOrTraversal
>
{
private:
struct enabler {}; // a private type avoids misuse
public:
node_iter()
: node_iter::iterator_adaptor_(0) {}
explicit node_iter(Value* p)
: node_iter::iterator_adaptor_(p) {}
template <class OtherValue>
node_iter(
node_iter<OtherValue> const& other
, typename boost::enable_if<
boost::is_convertible<OtherValue*,Value*>
, enabler
>::type = enabler()
)
: node_iter::iterator_adaptor_(other.base()) {}
private:
friend class boost::iterator_core_access;
void increment() { this->base_reference() = this->base()->next(); }
};
Note that the example only provides a default constructor, a constructor taking a node pointer, a generalized copy constructor that only accepts elements that can be converted to a node pointer, and an increment function. The increment function is an implementation detail that is shared by both operator++() and operator++(int).
All the other boiler-plate is automatically being generated by deriving from boost::iterator_adaptor. That includes all the nested typedef that you could also get from deriving from std::iterator, as well as all the overloaded operators (++, *, ->, ==, !=, advance) and anything else to make it a fully Standard conforming iterator.
By passing a Value const* and using a typedef you can define a const_iterator that reuses all your code with the appropriate modifications. Studying the example now will save you enormously down the road.