std::ranges::replace, std::ranges::replace_if
Defined in header <algorithm>
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Call signature |
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(1) | ||
template< std::input_iterator I, std::sentinel_for<I> S, class T1, class T2, class Proj = std::identity > |
(since C++20) (until C++26) |
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template< std::input_iterator I, std::sentinel_for<I> S, class Proj = std::identity, |
(since C++26) | |
(2) | ||
template< ranges::input_range R, class T1, class T2, class Proj = std::identity > |
(since C++20) (until C++26) |
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template< ranges::input_range R, class Proj = std::identity, |
(since C++26) | |
(3) | ||
template< std::input_iterator I, std::sentinel_for<I> S, class T, class Proj = std::identity, |
(since C++20) (until C++26) |
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template< std::input_iterator I, std::sentinel_for<I> S, class Proj = std::identity, |
(since C++26) | |
(4) | ||
template< ranges::input_range R, class T, class Proj = std::identity, std::indirect_unary_predicate< |
(since C++20) (until C++26) |
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template< ranges::input_range R, class Proj = std::identity, class T = std::projected_value_t<ranges::iterator_t<R>, Proj>, |
(since C++26) | |
Replaces all elements satisfying specific criteria with new_value in the range [
first,
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.
Contents |
[edit] 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 |
[edit] Return value
An iterator equal to last.
[edit] Complexity
Exactly ranges::distance(first, last) applications of the corresponding predicate comp and any projection proj.
[edit] 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 |
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__cpp_lib_algorithm_default_value_type |
202403 |
(C++26) | List-initialization for algorithms (1-4) |
[edit] Possible implementation
replace |
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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::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*> 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 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&> 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 {}; |
[edit] Example
#include <algorithm> #include <array> #include <complex> #include <iostream> void println(const auto& v) { for (const auto& 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) { return 5 < 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)
[edit] See also
(C++20)(C++20) |
copies a range, replacing elements satisfying specific criteria with another value (algorithm function object) |
replaces all values satisfying specific criteria with another value (function template) |