std::ranges::replace, std::ranges::replace_if
| Defined in header <algorithm>
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| Call signature |
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| template< std::input_iterator I, std::sentinel_for<I> S, class T1, class T2, class Proj = std::identity > |
(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&> && |
(2) | (since C++20) |
| template< std::input_iterator I, std::sentinel_for<I> S, class T, class Proj = std::identity, |
(3) | (since C++20) |
| template< ranges::input_range R, class T, class Proj = std::identity, std::indirect_unary_predicate< |
(4) | (since C++20) |
Replaces all elements satisfying specific criteria with new_value in the range [first, last).
old_value, using std::invoke(proj, *i) == old_value to compare.pred evaluates to true, where evaluating expression is std::invoke(pred, std::invoke(proj, *i)).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 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 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
| First version |
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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{}; |
| Second version |
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
#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
| (C++20)(C++20) |
copies a range, replacing elements satisfying specific criteria with another value (niebloid) |
| replaces all values satisfying specific criteria with another value (function template) |