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

 

C++

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Feature test macros(C++20)

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Metaprogramming library(C++11)

General utilities library

Containers library

Iterators library

Ranges library(C++20)

Algorithms library

Strings library

Text processing library

Numerics library

Date and time library

Input/output library

Filesystem library(C++17)

Concurrency support library(C++11)

Execution control library(C++26)

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 Batch operations for_each for_each_n (C++17) Search operations all_ofany_ofnone_of (C++11)                (C++11)(C++11) countcount_if mismatch equal findfind_iffind_if_not (C++11) find_end find_first_of adjacent_find search search_n Modifying sequence operations Copy operations copycopy_if (C++11) copy_backward copy_n (C++11) move (C++11) move_backward (C++11) Swap operations swap iter_swap swap_ranges Transformation operations replacereplace_if transform replace_copyreplace_copy_if Generation operations fill fill_n generate generate_n Removing operations removeremove_if unique remove_copyremove_copy_if unique_copy Order-changing operations reverse reverse_copy rotate rotate_copy random_shuffleshuffle (until C++17)(C++11) shift_leftshift_right (C++20)(C++20) Sampling operations sample (C++17)	Sorting and related operations Partitioning operations partition partition_copy (C++11)   stable_partition is_partitioned (C++11) partition_point (C++11) Sorting operations sort stable_sort partial_sort partial_sort_copy is_sorted (C++11) is_sorted_until (C++11) nth_element Binary search operations (on partitioned ranges) lower_bound upper_bound equal_range binary_search Set operations (on sorted ranges) includes set_union set_intersection set_difference set_symmetric_difference Merge operations (on sorted ranges) merge inplace_merge Heap operations push_heap pop_heap make_heap sort_heap is_heap (C++11) is_heap_until (C++11) Minimum/maximum operations max min minmax (C++11) clamp (C++17) max_element min_element minmax_element (C++11) Lexicographical comparison operations lexicographical_compare lexicographical_compare_three_way (C++20) Permutation operations next_permutation prev_permutation is_permutation (C++11) C library qsort bsearch
Numeric operations
iota (C++11) inner_product adjacent_difference    accumulate reduce (C++17) transform_reduce (C++17)	partial_sum inclusive_scan (C++17)    exclusive_scan (C++17) transform_inclusive_scan (C++17) transform_exclusive_scan (C++17)
Operations on uninitialized memory
uninitialized_copy uninitialized_move (C++17)    uninitialized_fill uninitialized_copy_n (C++11) uninitialized_move_n (C++17) uninitialized_fill_n	destroy (C++17) destroy_n (C++17) destroy_at (C++17) construct_at (C++20)       uninitialized_default_construct (C++17) uninitialized_value_construct (C++17) uninitialized_default_construct_n (C++17) uninitialized_value_construct_n (C++17)

 

Constrained algorithms

All names in this menu belong to namespace std::ranges

Non-modifying sequence operations

all_ofany_ofnone_of for_each for_each_n    countcount_if adjacent_find mismatch equal lexicographical_compare    containscontains_subrange (C++23)(C++23) findfind_iffind_if_not find_lastfind_last_iffind_last_if_not (C++23)(C++23)(C++23)   find_end find_first_of search search_n starts_with (C++23) ends_with (C++23)

Modifying sequence operations

copycopy_if copy_n copy_backward    move move_backward shift_leftshift_right (C++23)(C++23)   fill fill_n generate generate_n    transform swap_ranges    shuffle sample removeremove_if replacereplace_if reverse rotate remove_copyremove_copy_if    unique replace_copyreplace_copy_if reverse_copy rotate_copy unique_copy

Partitioning operations

is_partitioned    partition_point    partition    partition_copy    stable_partition

Sorting operations

is_sorted is_sorted_until     sort stable_sort         partial_sort       nth_element partial_sort_copy

Binary search operations (on sorted ranges)

lower_bound         upper_bound         binary_search      equal_range

Set operations (on sorted ranges)

merge inplace_merge       set_difference set_intersection    set_union          includes set_symmetric_difference

Heap operations

is_heap is_heap_until       make_heap           sort_heap push_heap pop_heap

Minimum/maximum operations

max max_element         min min_element         minmax minmax_element     clamp

Permutation operations

is_permutation      next_permutation    prev_permutation

Fold operations

fold_left (C++23) fold_left_first (C++23)   fold_right (C++23) fold_right_last (C++23)   fold_left_with_iter (C++23) fold_left_first_with_iter (C++23)

Numeric operations iota (C++23)             Random number generation generate_random (C++26)

Operations on uninitialized storage

construct_at    destroy destroy_n destroy_at uninitialized_copy    uninitialized_move uninitialized_fill uninitialized_copy_n    uninitialized_move_n uninitialized_fill_n uninitialized_default_construct uninitialized_default_construct_n uninitialized_value_construct uninitialized_value_construct_n

Return types

in_fun_result in_in_result in_found_result    in_out_result in_in_out_result    in_out_out_result    min_max_result out_value_result (C++23) in_value_result (C++23)

 

Defined in header <algorithm>
Call signature
	(1)
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 ={});			(since C++20) (until C++26)
template<std::input_iterator I, std::sentinel_for<I> S,           class Proj =std::identity,           class T1 = std::projected_value_t<I, Proj>, class T2 = T1 > 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 ={});			(since C++26)
		(2)
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*> constexprranges::borrowed_iterator_t<R>     replace( R&& r, const T1& old_value,              const T2& new_value, Proj proj ={});				(since C++20) (until C++26)
template<ranges::input_range R,           class Proj =std::identity,           class T1 = std::projected_value_t<ranges::iterator_t<R>, Proj>,           class T2 = T1 > 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*> constexprranges::borrowed_iterator_t<R>     replace( R&& r, const T1& old_value,              const T2& new_value, Proj proj ={});				(since C++26)
			(3)
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 ={});					(since C++20) (until C++26)
template<std::input_iterator I, std::sentinel_for<I> S,           class Proj =std::identity,           class T = std::projected_value_t<I, Proj>,           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 ={});					(since C++26)
				(4)
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&> constexprranges::borrowed_iterator_t<R>     replace_if( R&& r, Pred pred, const T& new_value, Proj proj ={});						(since C++20) (until C++26)
template<ranges::input_range R, class Proj =std::identity,           class T = std::projected_value_t<ranges::iterator_t<R>, Proj>,           std::indirect_unary_predicate<               std::projected<ranges::iterator_t<R>, Proj>> Pred > requires std::indirectly_writable<ranges::iterator_t<R>, const T&> constexprranges::borrowed_iterator_t<R>     replace_if( R&& r, Pred pred, const T& new_value, Proj proj ={});						(since C++26)

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 algorithm function objects (informally known as 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.

Parameters

first, last	-	the iterator-sentinel pair defining 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).

Feature-test macro	Value	Std	Feature
__cpp_lib_algorithm_default_value_type	202403	(C++26)	List-initialization for algorithms (1-4)

Possible implementation

replace (1,2)
struct replace_fn {template<std::input_iterator I, std::sentinel_for<I> S, class Proj =std::identity, class T1 = std::projected_value_t<I, Proj>, class T2 = T1> 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 Proj =std::identityclass T1 = std::projected_value_t<ranges::iterator_t<R>, Proj>, class T2 = T1> 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*>constexprranges::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));}};   inlineconstexpr replace_fn replace{};
replace_if (3,4)
struct replace_if_fn {template<std::input_iterator I, std::sentinel_for<I> S, class Proj =std::identity, class T = std::projected_value_t<I, Proj>, 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 Proj =std::identity, class T = std::projected_value_t<ranges::iterator_t<R>, Proj>std::indirect_unary_predicate<std::projected<ranges::iterator_t<R>, Proj>> Pred> requires std::indirectly_writable<ranges::iterator_t<R>, const T&>constexprranges::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));}};   inlineconstexpr replace_if_fn replace_if{};

Example

Run this code

#include <algorithm>#include <array>#include <complex>#include <iostream>   void println(constauto& v){for(constauto& e : v)std::cout<< e <<' ';std::cout<<'\n';}   int main(){namespace ranges = std::ranges;   std::array p{1, 6, 1, 6, 1, 6}; println(p); ranges::replace(p, 6, 9); println(p);   std::array q{1, 2, 3, 6, 7, 8, 4, 5}; println(q); ranges::replace_if(q, [](int x){return5< x;}, 5); println(q);   std::array<std::complex<double>, 2> nums{{{1, 3}, {1, 3}}}; println(nums);#ifdef __cpp_lib_algorithm_default_value_type ranges::replace(nums, {1, 3}, {4, 2});#else ranges::replace(nums, std::complex<double>{1, 3}, std::complex<double>{4, 2});#endif println(nums);}

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 (1,3) (1,3) (4,2) (4,2)

See also

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