std::remove_copy,std::remove_copy_if(3)

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
   >
   OutputIt remove_copy( InputIt first, InputIt (until C++20)
   last, OutputIt d_first,
   const T& value );
   template< class InputIt, class OutputIt, class T
   >
   constexpr OutputIt remove_copy( InputIt first, (since C++20)
   InputIt last, OutputIt d_first,
   const T& value );
   template< class ExecutionPolicy, class
   ForwardIt1, class ForwardIt2, class T >
   ForwardIt2 remove_copy( ExecutionPolicy&& (2) (since C++17)
   policy, ForwardIt1 first, ForwardIt1 last,
   ForwardIt2 d_first, const T& value );
   template< class InputIt, class OutputIt, class (1)
   UnaryPredicate >
   OutputIt remove_copy_if( InputIt first, InputIt (until C++20)
   last, OutputIt d_first,
   UnaryPredicate p );
   template< class InputIt, class OutputIt, class
   UnaryPredicate >
   constexpr OutputIt remove_copy_if( InputIt (3) (since C++20)
   first, InputIt last, OutputIt d_first,
   UnaryPredicate p );
   template< class ExecutionPolicy, class
   ForwardIt1, class ForwardIt2, class
   UnaryPredicate >
                        (4) (since C++17)
   ForwardIt2 remove_copy_if( ExecutionPolicy&&
   policy, ForwardIt1 first, ForwardIt1 last,
   ForwardIt2 d_first, UnaryPredicate p );
   Copies elements from the range [first, last), to another range beginning at d_first,
   omitting the elements which satisfy specific criteria. Source and destination ranges
   cannot overlap.
   1) Ignores all elements that are equal to value.
   3) Ignores all elements for which predicate p returns true.
   2,4) Same as (1,3), but executed according to policy. These overloads do not
   participate in overload resolution unless
   std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>
   (until C++20)
   std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>
   (since C++20) is true.

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.
   -
   UnaryPredicate must meet the requirements of Predicate.

Return value
   Iterator to the element past the last element copied.

Complexity
   Exactly std::distance(first, last) applications of the predicate.
   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

First version
   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;
   }

Second version
   template<class InputIt, class OutputIt, class UnaryPredicate>
   OutputIt remove_copy_if(InputIt first, InputIt last,
                        OutputIt d_first, UnaryPredicate p)
   {
       for (; first != last; ++first) {
           if (!p(*first)) {
               *d_first++ = *first;
           }
       }
       return d_first;
   }

Example
   The following code outputs a string while erasing the hash characters '#' on the
   fly. // Run this code
 #include <algorithm>
 #include <iterator>
 #include <string>
 #include <iostream>
 #include <iomanip>
 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";
 }

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

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)