std::ranges::replace_copy, std::ranges::replace_copy_if, std::ranges::replace_copy_result, std::ranges::replace_copy_if_result

Defined in header `<algorithm>`
Call signature
template< std::input_iterator I, std::sentinel_for<I> S, class T1, class T2, std::output_iterator<const T2&> O, class Proj = std::identity > requires std::indirectly_copyable<I, O> && std::indirect_binary_predicate<ranges::equal_to, std::projected<I, Proj>, const T1*> constexpr replace_copy_result<I, O> replace_copy( I first, S last, O result, const T1& old_value, const T2& new_value, Proj proj = {} );	(1)	(since C++20)
template< ranges::input_range R, class T1, class T2, std::output_iterator<const T2&> O, 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 T1*> constexpr replace_copy_result<ranges::borrowed_iterator_t<R>, O> replace_copy( R&& r, O result, const T1& old_value, const T2& new_value, Proj proj = {} );	(2)	(since C++20)
template< std::input_iterator I, std::sentinel_for<I> S, class T, std::output_iterator<const T&> O, class Proj = std::identity, std::indirect_unary_predicate<std::projected<I, Proj>> Pred > requires std::indirectly_copyable<I, O> constexpr replace_copy_if_result<I, O> replace_copy_if( I first, S last, O result, Pred pred, const T& new_value, Proj proj = {} );	(3)	(since C++20)
template< ranges::input_range R, class T, std::output_iterator<const T&> 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 replace_copy_if_result<ranges::borrowed_iterator_t<R>, O> replace_copy_if( R&& r, O result, Pred pred, const T& new_value, Proj proj = {} );	(4)	(since C++20)
Helper types
template< class I, class O > using replace_copy_result = ranges::in_out_result<I, O>;	(5)	(since C++20)
template< class I, class O > using replace_copy_if_result = ranges::in_out_result<I, O>;	(6)	(since C++20)

Copies the elements from the source range [first, last) to the destination range beginning at result, replacing all elements satisfying specific criteria with new_value. The behavior is undefined if the source and destination ranges overlap.

1) Replaces all elements that are equal to old_value, using std::invoke(proj, *(first + (i - result))) == old_value to compare.

3) Replaces all elements for which the predicate pred evaluates to true, where the evaluating expression is std::invoke(pred, std::invoke(proj, *(first + (i - result)))).

2,4) Same as (1,3), but uses r as the soruce 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 range of elements to copy
r	-	the range of elements to copy
result	-	the beginning of the destination range
old_value	-	the value of elements to replace
new_value	-	the value to use as a replacement
pred	-	predicate to apply to the projected elements
proj	-	projection to apply to the elements.

Return value

{last, result + N}, where

1,3) N = ranges::distance(first, last);

2,4) N = ranges::distance(r).

Complexity

Exactly N applications of the corresponding predicate comp and any projection proj.

Possible implementation

First version

struct replace_copy_fn {
    template <std::input_iterator I, std::sentinel_for<I> S, class T1, class T2,
             std::output_iterator<const T2&> O, class Proj = std::identity>
    requires std::indirectly_copyable<I, O> &&
             std::indirect_binary_predicate<ranges::equal_to, std::projected<I, Proj>,
             const T1*>
    constexpr ranges::replace_copy_result<I, O>
    operator()( I first, S last, O result, const T1& old_value, const T2& new_value,
                Proj proj = {} ) const {
        for (; first != last; ++first, ++result) {
            *result = (std::invoke(proj, *first) == old_value) ? new_value : *first;
        }
        return {std::move(first), std::move(result)};
    }
 
    template <ranges::input_range R, class T1, class T2,
             std::output_iterator<const T2&> O, 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 T1*>
    constexpr ranges::replace_copy_result<ranges::borrowed_iterator_t<R>, O>
    operator()( R&& r, O result, const T1& old_value, const T2& new_value,
                Proj proj = {} ) const {
        return (*this)(ranges::begin(r), ranges::end(r), std::move(result),
                       old_value, new_value, std::move(proj));
    }
};
 
inline constexpr replace_copy_fn replace_copy{};

Second version

struct replace_copy_if_fn {
    template <std::input_iterator I, std::sentinel_for<I> S, class T,
             std::output_iterator<const T&> O,
             class Proj = std::identity, std::indirect_unary_predicate<
             std::projected<I, Proj>> Pred>
    requires std::indirectly_copyable<I, O>
    constexpr ranges::replace_copy_if_result<I, O>
    operator()( I first, S last, O result, Pred pred, const T& new_value,
                Proj proj = {} ) const {
        for (; first != last; ++first, ++result) {
             *result = std::invoke(pred, std::invoke(proj, *first)) ? new_value : *first;
        }
        return {std::move(first), std::move(result)};
    }
 
    template <ranges::input_range R, class T, std::output_iterator<const T&> 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::replace_copy_if_result<ranges::borrowed_iterator_t<R>, O>
    operator()( R&& r, O result, Pred pred, const T& new_value,
                Proj proj = {} ) const {
        return (*this)(ranges::begin(r), ranges::end(r), std::move(result),
                       std::move(pred), new_value, std::move(proj));
    }
};
 
inline constexpr replace_copy_if_fn replace_copy_if{};

Example

Run this code

#include <algorithm>
#include <array>
#include <iostream>
#include <vector>
 
int main()
{
    auto print = [](const auto rem, const auto& v) {
        for (std::cout << rem << ": "; const auto& e : v)
            std::cout << e << ' ';
        std::cout << '\n';
    };
 
    std::vector<int> o;
 
    std::array p{1, 6, 1, 6, 1, 6};
    o.resize(p.size());
    print("p", p);
    std::ranges::replace_copy(p, o.begin(), 6, 9);
    print("o", o);
 
    std::array q{1, 2, 3, 6, 7, 8, 4, 5};
    o.resize(q.size());
    print("q", q);
    std::ranges::replace_copy_if(q, o.begin(), [](int x){ return 5 < x; }, 5);
    print("o", o);
}

Output:

p: 1 6 1 6 1 6 
o: 1 9 1 9 1 9 
q: 1 2 3 6 7 8 4 5 
o: 1 2 3 5 5 5 4 5

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::replaceranges::replace_if (C++20)(C++20)	replaces all values satisfying specific criteria with another value (niebloid)
replace_copyreplace_copy_if	copies a range, replacing elements satisfying specific criteria with another value (function template)