std::ranges::replace, std::ranges::replace_if - cppreference.com (original) (raw)

| Defined in header | | | | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | --------------------------- | | 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*> constexpr ranges::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*> constexpr ranges::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&> constexpr ranges::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&> constexpr ranges::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).

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

[edit] 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

[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
__cpp_lib_algorithm_default_value_type	202403	(C++26)	List-initialization for algorithms (1-4)

[edit] 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::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 (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 (!(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 #include #include #include 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, 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{1, 3}, std::complex{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)