std::remove_copy, std::remove_copy_if
(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 all following conditions are satisfied:
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.
[edit] Parameters
first, last
-
the pair of iterators defining the source
range of elements to copy
d_first
-
the beginning of the destination range
value
-
the value of the elements not to copy
Type requirements
-
UnaryPred must meet the requirements of
Predicate.
[edit] Return value
Iterator to the element past the last element copied.
[edit] 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.
[edit] 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.
[edit] 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;
} |
[edit] Example
#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)
[edit] 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
|
[edit] See also
removes elements satisfying specific criteria
(function template) [edit]
copies a range of elements to a new location
(function template) [edit]
copies a range dividing the elements into two groups
(function template) [edit]
copies a range of elements omitting those that satisfy specific criteria
(algorithm function object)[edit]