std::copy, std::copy_if

 

C++

Language

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

 

Algorithm library

Functions
Non-modifying sequence operations
all_of any_of none_of (C++11) (C++11) (C++11) for_each count count_if mismatch equal	find find_if find_if_not (C++11) find_end find_first_of adjacent_find search search_n
Modifying sequence operations
copy copy_if (C++11) copy_n (C++11) copy_backward move (C++11) move_backward (C++11) fill fill_n transform generate generate_n remove remove_if remove_copy remove_copy_if	replace replace_if replace_copy replace_copy_if swap swap_ranges iter_swap reverse reverse_copy rotate rotate_copy random_shuffle shuffle   (C++11) unique unique_copy
Partitioning operations
is_partitioned (C++11) partition partition_copy (C++11)	stable_partition partition_point (C++11)
Sorting operations (on sorted ranges)
is_sorted (C++11) is_sorted_until (C++11) sort	partial_sort partial_sort_copy stable_sort nth_element
Binary search operations (on sorted ranges)
lower_bound upper_bound	binary_search equal_range
Set operations (on sorted ranges)
merge inplace_merge includes	set_difference set_intersection set_symmetric_difference set_union
Heap operations
is_heap is_heap_until (C++11) make_heap	push_heap pop_heap sort_heap
Minimum/maximum operations
max max_element min min_element minmax (C++11) minmax_element (C++11)	lexicographical_compare is_permutation (C++11) next_permutation prev_permutation
Numeric operations
iota (C++11) accumulate inner_product	adjacent_difference partial_sum
C library
qsort	bsearch

 

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.

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. ​

Return value

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

Complexity

1) Exactly last - first assignments

2) Exactly last - first applications of the predicate

Possible implementation

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

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

See also

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