std::ranges::replace, std::ranges::replace_if

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

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

 

Algorithm library

Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
is_execution_policy (C++17)	execution::seqexecution::parexecution::par_unseqexecution::unseq (C++17)(C++17)(C++17)(C++20)	execution::sequenced_policyexecution::parallel_policyexecution::parallel_unsequenced_policyexecution::parallel_unsequenced (C++17)(C++17)(C++17)(C++20)
Non-modifying sequence operations
all_ofany_ofnone_of (C++11)(C++11)(C++11) for_each for_each_n (C++17)	countcount_if mismatch equal adjacent_find	search search_n lexicographical_compare lexicographical_compare_three_way (C++20)	findfind_iffind_if_not (C++11) find_end find_first_of
Modifying sequence operations
copycopy_if (C++11) copy_n (C++11) copy_backward move (C++11) move_backward (C++11) shift_leftshift_right (C++20)(C++20) transform	fill fill_n generate generate_n swap iter_swap swap_ranges sample (C++17)	removeremove_if replacereplace_if reverse rotate unique random_shuffle (until C++17)	remove_copyremove_copy_if replace_copyreplace_copy_if reverse_copy rotate_copy unique_copy shuffle (C++11)
Partitioning operations
is_partitioned (C++11) partition_point (C++11)	partition partition_copy (C++11)	stable_partition
Sorting operations
is_sorted (C++11) is_sorted_until (C++11)	sort stable_sort	partial_sort partial_sort_copy	nth_element
Binary search operations
lower_bound	upper_bound	binary_search	equal_range
Set operations (on sorted ranges)
merge inplace_merge	set_difference set_intersection	set_symmetric_difference set_union	includes
Heap operations
is_heap (C++11) is_heap_until (C++11)	make_heap sort_heap	push_heap pop_heap
Minimum/maximum operations
max max_element	min min_element	minmax (C++11) minmax_element (C++11)	clamp (C++17)
Permutations
is_permutation (C++11)	next_permutation	prev_permutation
Numeric operations
iota (C++11) inner_product adjacent_difference	accumulate reduce (C++17) transform_reduce (C++17)	transform_inclusive_scan (C++17) transform_exclusive_scan (C++17)	partial_sum inclusive_scan (C++17) exclusive_scan (C++17)
Operations on uninitialized storage
uninitialized_copy uninitialized_move (C++17) uninitialized_fill	uninitialized_copy_n (C++11) uninitialized_move_n (C++17) uninitialized_fill_n	uninitialized_default_construct (C++17) uninitialized_value_construct (C++17) uninitialized_default_construct_n (C++17) uninitialized_value_construct_n (C++17)	destroy (C++17) destroy_n (C++17) destroy_at (C++17) construct_at (C++20)
C library
qsort	bsearch

 

Constrained algorithms

Non-modifying sequence operations
ranges::all_ofranges::any_ofranges::none_of ranges::for_each ranges::for_each_n ranges::lexicographical_compare      ranges::adjacent_find	ranges::countranges::count_if ranges::mismatch ranges::equal ranges::containsranges::contains_subrange (C++23)(C++23)	ranges::findranges::find_ifranges::find_if_not ranges::find_lastranges::find_last_ifranges::find_last_if_not (C++23)(C++23)(C++23)	ranges::find_end ranges::find_first_of ranges::search ranges::search_n ranges::starts_with (C++23) ranges::ends_with (C++23)
Modifying sequence operations
ranges::copyranges::copy_if ranges::copy_n ranges::copy_backward ranges::move ranges::move_backward ranges::shift_leftranges::shift_right (C++23)(C++23)   ranges::transform	ranges::fill ranges::fill_n ranges::generate ranges::generate_n ranges::swap_ranges ranges::shuffle ranges::sample	ranges::removeranges::remove_if ranges::replaceranges::replace_if ranges::reverse ranges::rotate ranges::unique	ranges::remove_copyranges::remove_copy_if ranges::replace_copyranges::replace_copy_if ranges::reverse_copy ranges::rotate_copy ranges::unique_copy
Partitioning operations
ranges::is_partitioned ranges::partition_point	ranges::partition ranges::partition_copy	ranges::stable_partition
Sorting operations
ranges::is_sorted ranges::is_sorted_until	ranges::sort ranges::stable_sort	ranges::partial_sort ranges::partial_sort_copy	ranges::nth_element
Binary search operations
ranges::lower_bound	ranges::upper_bound	ranges::binary_search	ranges::equal_range
Set operations (on sorted ranges)
ranges::merge ranges::inplace_merge	ranges::set_difference ranges::set_intersection	ranges::set_symmetric_difference    ranges::set_union	ranges::includes
Heap operations
ranges::is_heap ranges::is_heap_until	ranges::make_heap ranges::sort_heap	ranges::push_heap ranges::pop_heap
Minimum/maximum operations
ranges::max ranges::max_element	ranges::min ranges::min_element	ranges::minmax ranges::minmax_element	ranges::clamp
Permutations
ranges::is_permutation	ranges::next_permutation	ranges::prev_permutation
Numeric operations
ranges::iota (C++23)
Fold operations
ranges::fold_left (C++23) ranges::fold_left_first (C++23)	ranges::fold_right (C++23) ranges::fold_right_last (C++23)	ranges::fold_left_with_iter (C++23) ranges::fold_left_first_with_iter (C++23)
Operations on uninitialized storage
ranges::construct_at ranges::destroy ranges::destroy_n ranges::destroy_at	ranges::uninitialized_copy    ranges::uninitialized_move ranges::uninitialized_fill	ranges::uninitialized_copy_n    ranges::uninitialized_move_n ranges::uninitialized_fill_n	ranges::uninitialized_default_construct ranges::uninitialized_default_construct_n    ranges::uninitialized_value_construct ranges::uninitialized_value_construct_n
Return types
ranges::in_fun_result ranges::in_in_result ranges::in_found_result	ranges::in_out_result ranges::in_in_out_result	ranges::in_out_out_result ranges::min_max_result	ranges::out_value_result (C++23) ranges::in_value_result (C++23)

 

Defined in header <algorithm>
Call signature
template< std::input_iterator I, std::sentinel_for<I> S, class T1, class T2,           class Proj = std::identity > requires std::indirectly_writable<I, const T2&> &&          std::indirect_binary_predicate<ranges::equal_to,              std::projected<I, Proj>, const T1*> constexpr I     replace( I first, S last, const T1& old_value, const T2& new_value,              Proj proj = {} );	(1)	(since C++20)
template< ranges::input_range R, class T1, class T2, class Proj = std::identity > requires std::indirectly_writable<ranges::iterator_t<R>, const T2&> &&          std::indirect_binary_predicate<ranges::equal_to,              std::projected<ranges::iterator_t<R>, Proj>, const T1*> constexpr ranges::borrowed_iterator_t<R>     replace( R&& r, 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,           class Proj = std::identity,           std::indirect_unary_predicate<std::projected<I, Proj>> Pred > requires std::indirectly_writable<I, const T&> constexpr I     replace_if( I first, S last, Pred pred, const T& new_value, Proj proj = {} );	(3)	(since C++20)
template< ranges::input_range R, class T, class Proj = std::identity,           std::indirect_unary_predicate<               std::projected<ranges::iterator_t<R>, Proj>> Pred > requires std::indirectly_writable<ranges::iterator_t<R>, const T&> constexpr ranges::borrowed_iterator_t<R>     replace_if( R&& r, Pred pred, const T& new_value, Proj proj = {} );	(4)	(since C++20)

Replaces all elements satisfying specific criteria with new_value in the range [first, last).

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

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

2,4) Same as (1,3), but uses r as the 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 cannot be specified when calling any of them.
• None of them are visible to argument-dependent lookup.
• When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.

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

Parameters

first, last	-	the range of elements to process
r	-	the range of elements to process
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

An iterator equal to last.

Complexity

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

Notes

Because the algorithm takes old_value and new_value by reference, it may have unexpected behavior if either is a reference to an element of the range [first, last).

Possible implementation

replace
struct replace_fn { template<std::input_iterator I, std::sentinel_for<I> S, class T1, class T2, class Proj = std::identity> requires std::indirectly_writable<I, const T2&> && std::indirect_binary_predicate< ranges::equal_to, std::projected<I, Proj>, const T1*> constexpr I operator()(I first, S last, const T1& old_value, const T2& new_value, Proj proj = {}) const { for (; first != last; ++first) if (old_value == std::invoke(proj, *first)) *first = new_value; return first; }   template<ranges::input_range R, class T1, class T2, class Proj = std::identity> requires std::indirectly_writable<ranges::iterator_t<R>, const T2&> && std::indirect_binary_predicate<ranges::equal_to, std::projected<ranges::iterator_t<R>, Proj>, const T1*> constexpr ranges::borrowed_iterator_t<R> operator()(R&& r, const T1& old_value, const T2& new_value, Proj proj = {}) const { return (*this)(ranges::begin(r), ranges::end(r), old_value, new_value, std::move(proj)); } };   inline constexpr replace_fn replace {};
replace_if
struct replace_if_fn { template<std::input_iterator I, std::sentinel_for<I> S, class T, class Proj = std::identity, std::indirect_unary_predicate< std::projected<I, Proj>> Pred> requires std::indirectly_writable<I, const T&> constexpr I operator()(I first, S last, Pred pred, const T& new_value, Proj proj = {}) const { for (; first != last; ++first) if (!!std::invoke(pred, std::invoke(proj, *first))) *first = new_value; return std::move(first); }   template<ranges::input_range R, class T, class Proj = std::identity, std::indirect_unary_predicate<std::projected<ranges::iterator_t<R>, Proj>> Pred> requires std::indirectly_writable<ranges::iterator_t<R>, const T&> constexpr ranges::borrowed_iterator_t<R> operator()(R&& r, Pred pred, const T& new_value, Proj proj = {}) const { return (*this)(ranges::begin(r), ranges::end(r), std::move(pred), new_value, std::move(proj)); } };   inline constexpr replace_if_fn replace_if {};

Example

Run this code

#include <algorithm>
#include <array>
#include <iostream>
 
int main()
{
    auto print = [](const auto& v)
    {
        for (const auto& e : v)
            std::cout << e << ' ';
        std::cout << '\n';
    };
 
    std::array p {1, 6, 1, 6, 1, 6};
    print(p);
    std::ranges::replace(p, 6, 9);
    print(p);
 
    std::array q {1, 2, 3, 6, 7, 8, 4, 5};
    print(q);
    std::ranges::replace_if(q, [](int x) { return 5 < x; }, 5);
    print(q);
}

Output:

1 6 1 6 1 6
1 9 1 9 1 9
1 2 3 6 7 8 4 5
1 2 3 5 5 5 4 5

See also

ranges::replace_copyranges::replace_copy_if (C++20)(C++20)	copies a range, replacing elements satisfying specific criteria with another value (niebloid)
replacereplace_if	replaces all values satisfying specific criteria with another value (function template)