std::remove_copy, std::remove_copy_if
From cppreference.com
| Defined in header <algorithm>
|
||
template< class InputIt, class OutputIt, class T >
OutputIt remove_copy( InputIt first, InputIt last,
OutputIt d_first, const T& value );
|
(1) | (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) | |
template< class InputIt, class OutputIt, class UnaryPred >
OutputIt remove_copy_if( InputIt first, InputIt last,
OutputIt d_first, UnaryPred p );
|
(2) | (constexpr since C++20) |
template< class ExecutionPolicy,
class ForwardIt1, class ForwardIt2, class T >
ForwardIt2 remove_copy( ExecutionPolicy&& policy,
ForwardIt1 first, ForwardIt1 last,
ForwardIt2 d_first, const T& value );
|
(3) | (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 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 source range [first, last) to the destination range beginning at d_first, ignoring the elements which satisfy specific criteria.
1)
remove_copy ignores all elements that are equal to value (using operator==).2)
remove_copy_if ignores all elements for which predicate p returns true.3,4) Same as (1,2), but executed according to
policy. These overloads participate in overload resolution only if the value of the following expression is
true:
|
|
(until C++20) |
|
|
(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 the source and destination ranges overlap, the behavior is undefined.
Parameters
| first, last | - | the pair of iterators defining the source range |
| d_first | - | the beginning of the destination range |
| value | - | the value of the elements not to copy |
| p | - | unary predicate which returns true if the element should not be copied. The expression |
| policy | - | the execution policy to use |
| 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
The past-the-end iterator of the destination range.
Complexity
Given \(\scriptsize N\)N as std::distance(first, last):
1) Exactly \(\scriptsize N\)N comparisons with
value using operator==.2) Exactly \(\scriptsize N\)N applications of the predicate
p.3) \(\scriptsize \mathcal{O}(N)\)(N) comparisons with
value using operator==.4) \(\scriptsize \mathcal{O}(N)\)(N) applications of the predicate
p.Exceptions
3,4) During the execution process:
- If the temporary memory resources required for parallelization are not available, std::bad_alloc is thrown.
- If an uncaught exception is thrown while accessing objects via an algorithm argument, the behavior is determined by the execution policy (for standard policies, std::terminate is invoked).
Notes
For parallel algorithm overloads, there may be a performance cost if ForwardIt1's value type is not MoveConstructible.
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_algorithm_default_value_type |
202403 |
(C++26) | List-initialization for algorithms (1,3) |
Possible implementation
| remove_copy |
|---|
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 |
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;
}
|
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, butthe value type of InputIt is not always T
|
required *d_first = *firstto be valid instead |
See also
(C++20)(C++20) |
copies a range of elements omitting those that satisfy specific criteria (algorithm function object) |
| removes elements satisfying specific criteria (function template & algorithm function object) | |
(C++20)(C++20) |
|
(C++11) |
copies a range of elements to a new location (function template & algorithm function object) |
(C++20)(C++20) |
|
(C++11) |
copies a range dividing the elements into two groups (function template & algorithm function object) |
(C++20) |