std::remove_copy, std::remove_copy_if

< cpp‎ | algorithm
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
Batch operations
Search operations
(C++11)                (C++11)(C++11)

Modifying sequence operations
Copy operations
Swap operations
Transformation operations
Generation operations
Removing operations
Order-changing operations
(until C++17)(C++11)
Sampling operations

Sorting and related operations
Partitioning operations
Sorting operations
Binary search operations
(on partitioned ranges)
Set operations (on sorted ranges)
Merge operations (on sorted ranges)
Heap operations
Minimum/maximum operations
Lexicographical comparison operations
Permutation operations
C library
Numeric operations
Operations on uninitialized memory
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)
template< class ExecutionPolicy,

          class ForwardIt1, class ForwardIt2, class T >
ForwardIt2 remove_copy( ExecutionPolicy&& policy,
                        ForwardIt1 first, ForwardIt1 last,

                        ForwardIt2 d_first, const T& value );
(2) (since C++17)
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 [firstlast), 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.


[edit] 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.

[edit] Return value

Iterator to the element past the last element copied.

[edit] Complexity

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

1,2) Exactly N comparisons with value using operator==.
3,4) Exactly 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

template<class InputIt, class OutputIt, class T>
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;
template<class InputIt, class OutputIt, class UnaryPred>
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

The following code outputs a string while erasing the hash characters '#' on the fly.

#include <algorithm>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <string>
int main()
    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";


before: "#Return #Value #Optimization"
after:  "Return Value Optimization"

[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