Copying Algorithms

Implementing Copy Algorithm

How can I implement my own version of std::ranges::copy()?

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Implementing your own version of std::ranges::copy() can be a great exercise to understand how the algorithm works.

The basic idea is to iterate over the source range and copy each element to the destination range. Here’s a simplified implementation:

#include <iostream>
#include <vector>

template <typename InputIt, typename OutputIt>
OutputIt my_copy(InputIt first,
  InputIt last, OutputIt d_first) {
  while (first != last) {
    *d_first++ = *first++; 
  }
  return d_first;
}

int main() {
  std::vector<int> Source{1, 2, 3, 4, 5};
  std::vector<int> Destination(5);

  my_copy(Source.begin(), Source.end(),
    Destination.begin()); 

  for (int Value : Destination) {
    std::cout << Value << ", ";
  }
}
1, 2, 3, 4, 5,

In this implementation:

  • my_copy() takes three parameters: the beginning and end of the source range, and the beginning of the destination range.
  • It uses a while loop to iterate from first to last, copying each element to the destination.

For more advanced functionality similar to std::ranges::copy(), you can add iterator traits to ensure compatibility with a wider range of iterator types. Here’s an enhanced version using iterator traits:

#include <iostream>
#include <vector>
#include <iterator>
#include <type_traits>

template <typename InputIt, typename OutputIt>
OutputIt my_copy(
  InputIt first, InputIt last, OutputIt d_first) {
  using ValueType =
    typename std::iterator_traits<InputIt>::value_type;

  static_assert(
    std::is_copy_assignable<ValueType>::value,
    "Value type must be copy assignable"
  );

  while (first != last) {
    *d_first++ = *first++; 
  }
  return d_first;
}

int main() {
  std::vector<int> Source{1, 2, 3, 4, 5};
  std::vector<int> Destination(5);

  my_copy(Source.begin(), Source.end(),
    Destination.begin()); 

  for (int Value : Destination) {
    std::cout << Value << ", ";
  }
}
1, 2, 3, 4, 5,

In this version:

  • std::iterator_traits is used to ensure the input iterator's value type is copy assignable.
  • This makes my_copy() more robust and similar to the standard library's approach.

Implementing your own copy algorithm helps you understand the intricacies of range-based algorithms and iterator concepts in C++.

Answers to questions are automatically generated and may not have been reviewed.

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