std::copy is a function in the C++ Standard Template Library (STL) that is used to copy a range of elements from one container to another. The function is defined in the
std::copy(first, last, result);
where "first" and "last" are iterators that define the range of elements to be copied, and "result" is an iterator to the destination container. The function returns an iterator to the end of the destination range.
Here is an example of using std::copy to copy all elements from an array to a vector:
#include <iostream>
#include <algorithm>
#include <vector>
int main()
{
int arr[] = {1, 2, 3, 4, 5};
std::vector<int> vec;
std::copy(std::begin(arr), std::end(arr), std::back_inserter(vec));
for(auto i : vec)
std::cout << i << " ";
return 0;
}
Output:
1 2 3 4 5
In this example, std::begin(arr) and std::end(arr) are used to get iterators to the beginning and end of the array, respectively. The std::back_inserter() function is used to get an iterator to the back of the vector, so that the elements are inserted at the end of the vector.
We can also use std::copy to copy elements to the specific position in the container, here is an example:
#include <iostream>
#include <algorithm>
#include <vector>
int main()
{
int arr[] = {1, 2, 3, 4, 5};
std::vector<int> vec = {10, 20, 30, 40, 50};
std::copy(std::begin(arr), std::end(arr), vec.begin() + 1);
for(auto i : vec)
std::cout << i << " ";
return 0;
}
Output:
10 1 2 3 4 5 20 30 40 50
In this example, vec.begin() + 1 is used to get an iterator to the second element of the vector, so that the elements are inserted at the second position of the vector.
It is important to note that std::copy will not resize the destination container. If the destination container is not large enough to hold all the elements in the source range, the behavior of the function is undefined.
Another important thing to note is that std::copy is a member of the C++98 standard, and it is not designed to be used with move-only types like std::unique_ptr. If you need to copy move-only types, you should use std::move_iterator and std::move_backward instead.
In conclusion, std::copy is a powerful and flexible function that can be used to copy elements from one container to another. It can be used with arrays, vectors, lists, and many other types of containers. It's a great tool to have in your toolbox when working with C++ containers.
std::move_iterator
std::move_iterator is a STL iterator adaptor that is used to move elements from one container to another. It is defined in the
std::move_iterator<Iterator>
Where Iterator is the type of iterator of the container you want to move elements from.
std::move_iterator is particularly useful when working with move-only types like std::unique_ptr, as it allows you to move elements from one container to another without making copies.
Here is an example of using std::move_iterator to move elements from a vector of unique pointers to another vector:
#include <iostream>
#include <algorithm>
#include <vector>
#include <memory>
int main()
{
std::vector<std::unique_ptr<int>> vec1;
vec1.push_back(std::make_unique<int>(1));
vec1.push_back(std::make_unique<int>(2));
vec1.push_back(std::make_unique<int>(3));
std::vector<std::unique_ptr<int>> vec2;
vec2.reserve(vec1.size());
std::move(std::make_move_iterator(vec1.begin()),
std::make_move_iterator(vec1.end()),
std::back_inserter(vec2));
for(const auto & i : vec2)
std::cout << *i << " ";
return 0;
}
Output:
1 2 3
In this example, std::make_move_iterator() is used to convert the iterators of vec1 to std::move_iterator, which allows the elements to be moved instead of copied. The std::move() function is then used to move the elements from vec1 to vec2.
It's important to note that after moving elements from one container to another with std::move_iterator, the elements in the original container are left in a valid but unspecified state, and it's not safe to use it afterwards.
std::move_backward
std::move_backward is a STL algorithm that moves elements from one container to another in reverse order. It is defined in the
std::move_backward(first, last, result);
Where "first" and "last" are iterators that define the range of elements to be moved, and "result" is an iterator to the destination container. The function returns an iterator to the last element moved.
std::move_backward is similar to std::move, but it moves elements in reverse order. It's particularly useful when moving elements from a container with a reversed order.
Here is an example of using std::move_backward to move elements from a vector of unique pointers to another vector in reverse order:
#include <iostream>
#include <algorithm>
#include <vector>
#include <memory>
int main()
{
std::vector<std::unique_ptr<int>> vec1;
vec1.push_back(std::make_unique<int>(1));
vec1.push_back(std::make_unique<int>(2));
## Popular questions
1. What is the syntax for the std::copy function?
- The syntax for the std::copy function is:
```std::copy(first, last, result);```
where "first" and "last" are iterators that define the range of elements to be copied, and "result" is an iterator to the destination container.
2. What is the function of the std::back_inserter function?
- The std::back_inserter function is an STL adapter that returns an iterator to the back of a container. It is typically used with the std::copy function to insert elements at the end of a container.
3. Can std::copy be used to copy elements to a specific position in a container?
- Yes, std::copy can be used to copy elements to a specific position in a container. To do this, you can pass an iterator to the desired position in the destination container as the "result" argument to the std::copy function.
4. What should be kept in mind when using std::copy with move-only types like std::unique_ptr?
- When using std::copy with move-only types like std::unique_ptr, it is important to keep in mind that std::copy is not designed to be used with these types and it will not work correctly. To copy move-only types, you should use std::move_iterator and std::move_backward instead.
5. What is the return type of std::copy function?
- std::copy function returns an iterator to the end of the destination range.
### Tag
Algorithm
