std::copy, std::copy_if

From Cppreference

Copies the elements in the range, defined by [first, last), to another range beginning at d_first. The second function only copies the elements for which the predicate pred returns true.

[edit] Parameters

[edit] Return value

Output iterator to the element in the destination range, one past the last element copied.

[edit] Complexity

1) Exactly last - first assignments

2) Exactly last - first applications of the predicate

[edit] Equivalent function

template<class InputIterator, class OutputIterator>
OutputIterator copy(InputIterator first, InputIterator last, 
                    OutputIterator d_first)
{
    while (first != last) {
        *d_first++ = *first++;
    }
    return d_first;
}

template<class InputIterator, class OutputIterator, class UnaryPredicate>
OutputIterator copy_if(InputIterator first, InputIterator last, 
                    OutputIterator d_first, UnaryPredicate pred)
{
    while (first != last) {
        if(pred(*first))
            *d_first++ = *first;
         first++;
    }
    return d_first;
}

[edit] Example

The following code uses copy to both copy the contents of one vector to another and to display the resulting vector:

#include <algorithm>
#include <iostream>
 
int main()
{
    std::vector<int> from_vector;
    for (int i = 0; i < 10; i++) {
        from_vector.push_back(i);
    }
 
    std::vector<int> to_vector(10);
 
    std::copy(from_vector.begin(), from_vector.end(), to_vector.begin());
 
    std::cout << "to_vector contains: ";
    std::copy(to_vector.begin(), to_vector.end(), 
              std::ostream_iterator<int>(std::cout, " "));
}

Output:

to_vector contains: 0 1 2 3 4 5 6 7 8 9

[edit] See also