std::copy, std::copy_if

From cppreference.com
 
 
 
Defined in header <algorithm>
template< class InputIterator, class OutputIterator >
OutputIterator copy( InputIterator first, InputIterator last, OutputIterator d_first );
(1)
template< class InputIterator, class OutputIterator, class UnaryPredicate >

OutputIterator copy_if( InputIterator first, InputIterator last,
                        OutputIterator d_first,

                        UnaryPredicate pred );
(2) (since C++11)

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.

Contents

[edit] Parameters

first, last - the range of elements to copy
d_first - the beginning of the destination range. If d_first is within [first, last), std::copy_backward must be used instead of std::copy.
pred - unary predicate which returns ​true for the required elements.

The signature of the predicate function should be equivalent to the following:

bool pred(const Type &a);

The signature does not need to have const &, but the function must not modify the objects passed to it.
The type Type must be such that an object of type InputIterator can be dereferenced and then implicitly converted to Type. ​

[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] Possible implementation

[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>
#include <vector>
#include <iterator>
 
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, " "));
    std::cout << std::endl;
}

Output:

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

[edit] See also

copies a range of elements in backwards order
(function template)
copies a range of elements omitting those that satisfy specific criteria
(function template)