std::remove_copy, std::remove_copy_if

 

C++

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Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

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Strings library

Containers library

Iterators library

Ranges library (C++20)

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Numerics library

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Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

Algorithm library

Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
is_execution_policy (C++17)   execution::seqexecution::parexecution::par_unseqexecution::unseq (C++17)    (C++17)(C++17)(C++20)	execution::sequenced_policyexecution::parallel_policyexecution::parallel_unsequenced_policyexecution::parallel_unsequenced (C++17)(C++17)(C++17)(C++20)
Non-modifying sequence operations Batch operations for_each for_each_n (C++17) Search operations all_ofany_ofnone_of (C++11)                (C++11)(C++11) countcount_if mismatch equal findfind_iffind_if_not (C++11) find_end find_first_of adjacent_find search search_n Modifying sequence operations Copy operations copycopy_if (C++11) copy_backward copy_n (C++11) move (C++11) move_backward (C++11) Swap operations swap iter_swap swap_ranges Transformation operations replacereplace_if transform replace_copyreplace_copy_if Generation operations fill fill_n generate generate_n Removing operations removeremove_if unique remove_copyremove_copy_if unique_copy Order-changing operations reverse reverse_copy rotate rotate_copy random_shuffleshuffle (until C++17)(C++11) shift_leftshift_right (C++20)(C++20) Sampling operations sample (C++17)	Sorting and related operations Partitioning operations partition partition_copy (C++11)   stable_partition is_partitioned (C++11) partition_point (C++11) Sorting operations sort stable_sort partial_sort partial_sort_copy is_sorted (C++11) is_sorted_until (C++11) nth_element Binary search operations (on partitioned ranges) lower_bound upper_bound equal_range binary_search Set operations (on sorted ranges) includes set_union set_intersection set_difference set_symmetric_difference Merge operations (on sorted ranges) merge inplace_merge Heap operations push_heap pop_heap make_heap sort_heap is_heap (C++11) is_heap_until (C++11) Minimum/maximum operations max min minmax (C++11) clamp (C++17) max_element min_element minmax_element (C++11) Lexicographical comparison operations lexicographical_compare lexicographical_compare_three_way (C++20) Permutation operations next_permutation prev_permutation is_permutation (C++11) C library qsort bsearch
Numeric operations
iota (C++11) inner_product adjacent_difference    accumulate reduce (C++17) transform_reduce (C++17)	partial_sum inclusive_scan (C++17)    exclusive_scan (C++17) transform_inclusive_scan (C++17) transform_exclusive_scan (C++17)
Operations on uninitialized memory
uninitialized_copy uninitialized_move (C++17)    uninitialized_fill uninitialized_copy_n (C++11) uninitialized_move_n (C++17) uninitialized_fill_n	destroy (C++17) destroy_n (C++17) destroy_at (C++17) construct_at (C++20)       uninitialized_default_construct (C++17) uninitialized_value_construct (C++17) uninitialized_default_construct_n (C++17) uninitialized_value_construct_n (C++17)

 

Defined in header <algorithm>
	(1)
template< class InputIt, class OutputIt, class T > OutputIt remove_copy( InputIt first, InputIt last,                       OutputIt d_first, const T& value );			(constexpr since C++20) (until C++26)
template< class InputIt, class OutputIt,           class T = typename std::iterator_traits                         <InputIt>::value_type > constexpr OutputIt remove_copy( InputIt first, InputIt last,                                 OutputIt d_first, const T& value );			(since C++26)
		(2)
template< class ExecutionPolicy,           class ForwardIt1, class ForwardIt2, class T > ForwardIt2 remove_copy( ExecutionPolicy&& policy,                         ForwardIt1 first, ForwardIt1 last,                         ForwardIt2 d_first, const T& value );				(since C++17) (until C++26)
template< class ExecutionPolicy,           class ForwardIt1, class ForwardIt2,           class T = typename std::iterator_traits                         <ForwardIt1>::value_type > ForwardIt2 remove_copy( ExecutionPolicy&& policy,                         ForwardIt1 first, ForwardIt1 last,                         ForwardIt2 d_first, const T& value );				(since C++26)
template< class InputIt, class OutputIt, class UnaryPred > OutputIt remove_copy_if( InputIt first, InputIt last,                          OutputIt d_first, UnaryPred p );			(3)	(constexpr since C++20)
template< class ExecutionPolicy,           class ForwardIt1, class ForwardIt2, class UnaryPred > ForwardIt2 remove_copy_if( ExecutionPolicy&& policy,                            ForwardIt1 first, ForwardIt1 last,                            ForwardIt2 d_first, UnaryPred p );			(4)	(since C++17)

Copies elements from the range [first, last), to another range beginning at d_first, omitting the elements which satisfy specific criteria.

1) Ignores all elements that are equal to value (using operator==).

3) Ignores all elements for which predicate p returns true.

2,4) Same as (1,3), but executed according to policy.

These overloads participate in overload resolution only if

std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true.	(until C++20)
std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true.	(since C++20)

If *d_first = *first is invalid(until C++20)*first is not writable to d_first(since C++20), the program is ill-formed.

If source and destination ranges overlap, the behavior is undefined.

Parameters

first, last	-	the range of elements to copy
d_first	-	the beginning of the destination range
value	-	the value of the elements not to copy
policy	-	the execution policy to use. See execution policy for details.
Type requirements
- InputIt must meet the requirements of LegacyInputIterator.
- OutputIt must meet the requirements of LegacyOutputIterator.
- ForwardIt1, ForwardIt2 must meet the requirements of LegacyForwardIterator.
- UnaryPred must meet the requirements of Predicate.

Return value

Iterator to the element past the last element copied.

Complexity

Given \(\scriptsize N\)N as std::distance(first, last):

1,2) Exactly \(\scriptsize N\)N comparisons with value using operator==.

3,4) Exactly \(\scriptsize N\)N applications of the predicate p.

For the overloads with an ExecutionPolicy, there may be a performance cost if ForwardIt1's value_type is not MoveConstructible.

Exceptions

The overloads with a template parameter named ExecutionPolicy report errors as follows:

• If execution of a function invoked as part of the algorithm throws an exception and ExecutionPolicy is one of the standard policies, std::terminate is called. For any other ExecutionPolicy, the behavior is implementation-defined.
• If the algorithm fails to allocate memory, std::bad_alloc is thrown.

Possible implementation

remove_copy (1)
template<class InputIt, class OutputIt, class T = typename std::iterator_traits<InputIt>::value_type> constexpr OutputIt remove_copy(InputIt first, InputIt last, OutputIt d_first, const T& value) { for (; first != last; ++first) if (!(*first == value)) *d_first++ = *first; return d_first; }
remove_copy_if (3)
template<class InputIt, class OutputIt, class UnaryPred> constexpr OutputIt remove_copy_if(InputIt first, InputIt last, OutputIt d_first, UnaryPred p) { for (; first != last; ++first) if (!p(*first)) *d_first++ = *first; return d_first; }

Notes

Feature-test macro	Value	Std	Feature
__cpp_lib_algorithm_default_value_type	202403	(C++26)	List-initialization for algorithms (1,2)

Example

Run this code

#include <algorithm>
#include <complex>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <string>
#include <vector>
 
int main()
{
    // Erase the hash characters '#' on the fly.
    std::string str = "#Return #Value #Optimization";
    std::cout << "before: " << std::quoted(str) << '\n';
 
    std::cout << "after:  \"";
    std::remove_copy(str.begin(), str.end(),
                     std::ostream_iterator<char>(std::cout), '#');
    std::cout << "\"\n";
 
    // Erase {1, 3} value on the fly.
    std::vector<std::complex<double>> nums{{2, 2}, {1, 3}, {4, 8}, {1, 3}};
    std::remove_copy(nums.begin(), nums.end(),
                     std::ostream_iterator<std::complex<double>>(std::cout),
    #ifdef __cpp_lib_algorithm_default_value_type
                     {1, 3}); // T gets deduced
    #else
                     std::complex<double>{1, 3});
    #endif
}

Output:

before: "#Return #Value #Optimization"
after:  "Return Value Optimization"
(2,2)(4,8)

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 779	C++98	T was required to be EqualityComparable, but the value type of ForwardIt is not always T	required *d_first = *first to be valid instead

See also

removeremove_if	removes elements satisfying specific criteria (function template)
copycopy_if (C++11)	copies a range of elements to a new location (function template)
partition_copy (C++11)	copies a range dividing the elements into two groups (function template)
ranges::remove_copyranges::remove_copy_if (C++20)(C++20)	copies a range of elements omitting those that satisfy specific criteria (niebloid)