std::ranges::remove_copy, std::ranges::remove_copy_if, std::ranges::remove_copy_result, std::ranges::remove_copy_if_result

Defined in header `<algorithm>`
Call signature
template< std::input_iterator I, std::sentinel_for<I> S, std::weakly_incrementable O, class T, class Proj = std::identity > requires std::indirectly_copyable<I, O> && std::indirect_binary_predicate<ranges::equal_to, std::projected<I, Proj>, const T*> constexpr remove_copy_result<I, O> remove_copy( I first, S last, O result, const T& value, Proj proj = {} );	(1)	(since C++20)
template< ranges::input_range R, std::weakly_incrementable O, class T, class Proj = std::identity > requires std::indirectly_copyable<ranges::iterator_t<R>, O> && std::indirect_binary_predicate<ranges::equal_to, std::projected<ranges::iterator_t<R>, Proj>, const T*> constexpr remove_copy_result<ranges::borrowed_iterator_t<R>, O> remove_copy( R&& r, O result, const T& value, Proj proj = {} );	(2)	(since C++20)
template< std::input_iterator I, std::sentinel_for<I> S, std::weakly_incrementable O, class Proj = std::identity, std::indirect_unary_predicate<std::projected<I, Proj>> Pred > requires std::indirectly_copyable<I, O> constexpr remove_copy_if_result<I, O> remove_copy_if( I first, S last, O result, Pred pred, Proj proj = {} );	(3)	(since C++20)
template< ranges::input_range R, std::weakly_incrementable O, class Proj = std::identity, std::indirect_unary_predicate< std::projected<ranges::iterator_t<R>, Proj>> Pred > requires std::indirectly_copyable<ranges::iterator_t<R>, O> constexpr remove_copy_if_result<ranges::borrowed_iterator_t<R>, O> remove_copy_if( R&& r, O result, Pred pred, Proj proj = {} );	(4)	(since C++20)
Helper types
template<class I, class O> using remove_copy_result = ranges::in_out_result<I, O>;	(5)	(since C++20)
template<class I, class O> using remove_copy_if_result = ranges::in_out_result<I, O>;	(6)	(since C++20)

Copies elements from the source range [first, last), to the destination range beginning at result, omitting the elements which (after being projected by proj) satisfy specific criteria. The behavior is undefined if the source and destination ranges overlap.

1) Ignores all elements that are equal to value.

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

2,4) Same as (1,3), but uses r as the source range, as if using ranges::begin(r) as first, and ranges::end(r) as last.

The function-like entities described on this page are niebloids, that is:

Explicit template argument lists may not be specified when calling any of them.
None of them is visible to argument-dependent lookup.
When one of them is found by normal unqualified lookup for the name to the left of the function-call operator, it inhibits argument-dependent lookup.

In practice, they may be implemented as function objects, or with special compiler extensions.

Parameters

first, last	-	the source range of elements
r	-	the source range of elements
result	-	the beginning of the destination range
value	-	the value of the elements not to copy
comp	-	the binary predicate to compare the projected elements
proj	-	the projection to apply to the elements

Return value

{last, result + N}, where N is the number of elements copied.

Complexity

Exactly ranges::distance(first, last) applications of the corresponding predicate comp and any projection proj.

Notes

The algorithm is stable, i.e. preserves the relative order of the copied elements.

Possible implementation

First version

struct remove_copy_fn {
  template <std::input_iterator I, std::sentinel_for<I> S, std::weakly_incrementable O,
           class T, class Proj = std::identity>
  requires std::indirectly_copyable<I, O> &&
           std::indirect_binary_predicate<ranges::equal_to, std::projected<I, Proj>, const T*>
  constexpr ranges::remove_copy_result<I, O>
  operator()( I first, S last, O result, const T& value, Proj proj = {} ) const {
      for (; !(first == last); ++first) {
          if (value != std::invoke(proj, *first)) {
              *result = *first;
              ++result;
          }
      }
      return {std::move(first), std::move(result)};
  }
 
  template <ranges::input_range R, std::weakly_incrementable O, class T,
           class Proj = std::identity>
  requires std::indirectly_copyable<ranges::iterator_t<R>, O> &&
           std::indirect_binary_predicate<ranges::equal_to,
           std::projected<ranges::iterator_t<R>, Proj>, const T*>
  constexpr ranges::remove_copy_result<ranges::borrowed_iterator_t<R>, O>
  operator()( R&& r, O result, const T& value, Proj proj = {} ) const {
      return (*this)(ranges::begin(r), ranges::end(r), std::move(result), value,
                     std::move(proj));
  }
};
inline constexpr remove_copy_fn remove_copy{};

Second version

struct remove_copy_if_fn {
  template <std::input_iterator I, std::sentinel_for<I> S, std::weakly_incrementable O,
           class Proj = std::identity,
           std::indirect_unary_predicate<std::projected<I, Proj>> Pred>
  requires std::indirectly_copyable<I, O>
  constexpr ranges::remove_copy_if_result<I, O>
  operator()( I first, S last, O result, Pred pred, Proj proj = {} ) const {
      for (; first != last; ++first) {
          if (false == std::invoke(pred, std::invoke(proj, *first))) {
              *result = *first;
              ++result;
          }
      }
      return {std::move(first), std::move(result)};
  }
 
  template <ranges::input_range R, std::weakly_incrementable O, class Proj = std::identity,
           std::indirect_unary_predicate<std::projected<ranges::iterator_t<R>, Proj>> Pred>
  requires std::indirectly_copyable<ranges::iterator_t<R>, O>
  constexpr ranges::remove_copy_if_result<ranges::borrowed_iterator_t<R>, O>
  operator()( R&& r, O result, Pred pred, Proj proj = {} ) const {
      return (*this)(ranges::begin(r), ranges::end(r), std::move(result), std::move(pred),
                     std::move(proj));
  }
};
inline constexpr remove_copy_if_fn remove_copy_if{};

Example

Run this code

#include <algorithm>
#include <array>
#include <complex>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <string_view>
#include <vector>
 
void print(const auto rem, const auto& v) {
    std::cout << rem << ' ';
    for (const auto& e : v) { std::cout << e << ' '; };
    std::cout << '\n';
}
 
int main()
{
    // Filter out the hash symbol from the given string.
    const std::string_view str{ "#Small #Buffer #Optimization" };
    std::cout << "before: " << std::quoted(str) << "\n";
 
    std::cout << "after:  \"";
    std::ranges::remove_copy(str.begin(), str.end(),
                             std::ostream_iterator<char>(std::cout), '#');
    std::cout << "\"\n";
 
 
    // Copy only the complex numbers with positive imaginary part.
    using Ci = std::complex<int>;
    constexpr std::array<Ci, 5> source{
        Ci{1,0}, Ci{0,1}, Ci{2,-1}, Ci{3,2}, Ci{4,-3}
    };
    std::vector<std::complex<int>> target;
 
    std::ranges::remove_copy_if(source,
        std::back_inserter(target),
        [](int imag){ return imag <= 0; },
        [](Ci z){ return z.imag(); }
    );
 
    print("source:", source);
    print("target:", target);
}

Output:

before: "#Small #Buffer #Optimization"
after:  "Small Buffer Optimization"
source: (1,0) (0,1) (2,-1) (3,2) (4,-3)
target: (0,1) (3,2)

Compiler support
Freestanding and hosted
Language
Standard library headers
Named requirements
Feature test macros (C++20)
Language support library
Concepts library (C++20)
Metaprogramming library (C++11)
Diagnostics library
General utilities library
Strings library
Containers library
Iterators library
Ranges library (C++20)
Algorithms library
Numerics library
Localizations library
Input/output library
Filesystem library (C++17)
Regular expressions library (C++11)
Concurrency support library (C++11)
Technical specifications
Symbols index
External libraries

ranges::removeranges::remove_if (C++20)(C++20)	removes elements satisfying specific criteria (niebloid)
ranges::copyranges::copy_if (C++20)(C++20)	copies a range of elements to a new location (niebloid)
ranges::copy_n (C++20)	copies a number of elements to a new location (niebloid)
ranges::copy_backward (C++20)	copies a range of elements in backwards order (niebloid)
ranges::replace_copyranges::replace_copy_if (C++20)(C++20)	copies a range, replacing elements satisfying specific criteria with another value (niebloid)
ranges::reverse_copy (C++20)	creates a copy of a range that is reversed (niebloid)
ranges::rotate_copy (C++20)	copies and rotate a range of elements (niebloid)
ranges::unique_copy (C++20)	creates a copy of some range of elements that contains no consecutive duplicates (niebloid)
remove_copyremove_copy_if	copies a range of elements omitting those that satisfy specific criteria (function template)