std::replace_copy,std::replace_copy_if(3)

NAME
std::replace_copy,std::replace_copy_if - std::replace_copy,std::replace_copy_if

Synopsis
   Defined in header <algorithm>
   template< class InputIt, class OutputIt, class T
   >
   OutputIt replace_copy( InputIt first, InputIt (until C++20)
   last, OutputIt d_first,
   const T& old_value, const T& new_value );
   template< class InputIt, class OutputIt, class T
   >
   constexpr OutputIt replace_copy( InputIt first, (since C++20)
   InputIt last, OutputIt d_first,
   const T& old_value, const T& new_value );
   template< class ExecutionPolicy, class
   ForwardIt1, class ForwardIt2, class T >
   ForwardIt2 replace_copy( ExecutionPolicy&& (2) (since C++17)
   policy, ForwardIt1 first, ForwardIt1 last,
   ForwardIt2 d_first, const T& old_value, const T&
   new_value );
   template< class InputIt, class OutputIt, class (1)
   UnaryPredicate, class T >
   OutputIt replace_copy_if( InputIt first, InputIt (until C++20)
   last, OutputIt d_first,
   UnaryPredicate p, const T& new_value );
   template< class InputIt, class OutputIt, class
   UnaryPredicate, class T >
   constexpr OutputIt replace_copy_if( InputIt (since C++20)
   first, InputIt last, OutputIt d_first, (3)
   UnaryPredicate p, const T& new_value );
   template< class ExecutionPolicy, class
   ForwardIt1, class ForwardIt2, class
   UnaryPredicate, class T >
   ForwardIt2 replace_copy_if( ExecutionPolicy&& (4) (since C++17)
   policy, ForwardIt1 first, ForwardIt1 last,
   ForwardIt2 d_first, UnaryPredicate p, const T&
   new_value );
   Copies the elements from the range [first, last) to another range beginning at
   d_first replacing all elements satisfying specific criteria with new_value. The
   source and destination ranges cannot overlap.
   1) Replaces all elements that are equal to old_value.
   3) Replaces 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
   old_value - the value of elements to replace
   policy - the execution policy to use. See execution policy for details.
                 unary predicate which returns true if the element value should be
                 replaced.
                 The expression p(v) must be convertible to bool for every argument v
   p - of type (possibly const) VT, where VT is the value type of InputIt,
                 regardless of value category, and must not modify v. Thus, a parameter
                 type of VT&is not allowed
                 , nor is VT unless for VT a move is equivalent to a copy
                 (since C++11).
   new_value - the value to use as replacement

Type requirements
   -
   InputIt must meet the requirements of LegacyInputIterator.
   -
   OutputIt must meet the requirements of LegacyOutputIterator.
   -
   ForwardIt1, ForwardIt2 must meet the requirements of LegacyForwardIterator.

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

Complexity
   Exactly last - first applications of the predicate.

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 replace_copy(InputIt first, InputIt last, OutputIt d_first,
                        const T& old_value, const T& new_value)
   {
       for (; first != last; ++first) {
           *d_first++ = (*first == old_value) ? new_value : *first;
       }
       return d_first;
   }

Second version
   template<class InputIt, class OutputIt,
            class UnaryPredicate, class T>
   OutputIt replace_copy_if(InputIt first, InputIt last, OutputIt d_first,
                        UnaryPredicate p, const T& new_value)
   {
       for (; first != last; ++first) {
           *d_first++ = p( *first ) ? new_value : *first;
       }
       return d_first;
   }

Example
   The following copy prints a vector, replacing all values over 5 with 99 on the fly. // Run this code
 #include <algorithm>
 #include <vector>
 #include <iostream>
 #include <iterator>
 #include <functional>
 int main()
 {
     std::vector<int> v{5, 7, 4, 2, 8, 6, 1, 9, 0, 3};
     std::replace_copy_if(v.begin(), v.end(),
                        std::ostream_iterator<int>(std::cout, " "),
                        [](int n){return n > 5;}, 99);
     std::cout << '\n';
 }

Output:
 5 99 4 2 99 99 1 99 0 3

See also
   replace replaces all values satisfying specific criteria with
   replace_if another value
                        (function template)
   remove removes elements satisfying specific criteria
   remove_if (function template)
   ranges::replace_copy copies a range, replacing elements satisfying specific
   ranges::replace_copy_if criteria with another value
   (C++20) (niebloid)
   (C++20)