NAME¶

std::remove_copy,std::remove_copy_if - std::remove_copy,std::remove_copy_if

Synopsis¶

Defined in header <algorithm>
template< class InputIt, class OutputIt,
class T >
(constexpr since
OutputIt remove_copy( InputIt first, C++20)
InputIt last, (until C++26)

OutputIt d_first,
const T& value );
template< class InputIt, class OutputIt,

class T = typename
std::iterator_traits

<InputIt>::value_type > (since C++26)
constexpr OutputIt remove_copy( InputIt
first, InputIt last,

OutputIt
d_first, const T& value );
template< class ExecutionPolicy,

class ForwardIt1, class
ForwardIt2, class T >
ForwardIt2 remove_copy( ExecutionPolicy&& (since C++17)
policy, (until C++26)
ForwardIt1 first,
ForwardIt1 last,

ForwardIt2
d_first, const T& value );
template< class ExecutionPolicy,
(1)
class ForwardIt1, class
ForwardIt2,
class T = typename
std::iterator_traits

<ForwardIt1>::value_type > (since C++26)
ForwardIt2 remove_copy( ExecutionPolicy&&
policy,
ForwardIt1 first,
ForwardIt1 last, (2)

ForwardIt2
d_first, const T& value );
template< class InputIt, class OutputIt,
class UnaryPred >

OutputIt remove_copy_if( InputIt first, (3) (constexpr since
InputIt last, C++20)

OutputIt d_first,
UnaryPred p );
template< class ExecutionPolicy,

class ForwardIt1, class
ForwardIt2, class UnaryPred >
ForwardIt2 remove_copy_if(
ExecutionPolicy&& policy, (4) (since C++17)
ForwardIt1
first, ForwardIt1 last,

ForwardIt2
d_first, UnaryPred p );

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
T was required to be EqualityComparable, but required *d_first =
LWG 779 C++98 the value type of ForwardIt is not always T *first
to be valid instead

See also¶

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