std::ranges::max
From cppreference.com
| Defined in header <algorithm>
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| Call signature |
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| template< class T, class Proj = std::identity, std::indirect_strict_weak_order< |
(since C++20) | |
| template< std::copyable T, class Proj = std::identity, std::indirect_strict_weak_order< |
(since C++20) | |
| template< ranges::input_range R, class Proj = std::identity, std::indirect_strict_weak_order< |
(since C++20) | |
Returns the greater of the given projected values.
1) Returns the greater of
a and b.2) Returns the first greatest value in the initializer list
r.3) Returns the first greatest value in the range
r.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.
Contents |
[edit] Parameters
| a, b | - | the values to compare |
| r | - | the range of values to compare |
| comp | - | comparison to apply to the projected elements |
| proj | - | projection to apply to the elements |
[edit] Return value
1) The greater of
a and b, according to their respective projected values. If they are equivalent, returns a.2-3) The greatest value in
r, according to the projection. If several values are equivalent to the greatest, returns the leftmost one. If the range is empty (as determined by ranges::distance(r)), the behavior is undefined.[edit] Complexity
1) Exactly one comparison.
2-3) Exactly ranges::distance(r) - 1 comparisons.
[edit] Possible implementation
struct max_fn { template<class T, class Proj = std::identity, std::indirect_strict_weak_order< std::projected<const T*, Proj>> Comp = ranges::less> constexpr const T& operator()(const T& a, const T& b, Comp comp = {}, Proj proj = {}) const { return std::invoke(comp, std::invoke(proj, a), std::invoke(proj, b)) ? b : a; } template<std::copyable T, class Proj = std::identity, std::indirect_strict_weak_order< std::projected<const T*, Proj>> Comp = ranges::less> constexpr const T operator()(std::initializer_list<T> r, Comp comp = {}, Proj proj = {}) const { return *ranges::max_element(r, std::ref(comp), std::ref(proj)); } template<ranges::input_range R, class Proj = std::identity, std::indirect_strict_weak_order< std::projected<ranges::iterator_t<R>, Proj>> Comp = ranges::less> requires std::indirectly_copyable_storable<ranges::iterator_t<R>, ranges::range_value_t<R>*> constexpr ranges::range_value_t<R> operator()(R&& r, Comp comp = {}, Proj proj = {}) const { using V = ranges::range_value_t<R>; if constexpr (ranges::forward_range<R>) { return static_cast<V>(*ranges::max_element(r, std::ref(comp), std::ref(proj))); } else { auto i = ranges::begin(r); auto s = ranges::end(r); V m(*i); while (++i != s) { if (std::invoke(comp, std::invoke(proj, m), std::invoke(proj, *i))) { m = *i; } } return m; } } }; inline constexpr max_fn max; |
[edit] Notes
Capturing the result of std::ranges::max by reference produces a dangling reference if one of the parameters is a temporary and that parameter is returned:
int n = 1; const int& r = std::ranges::max(n - 1, n + 1); // r is dangling
[edit] Example
Run this code
#include <algorithm> #include <iostream> #include <string> int main() { namespace ranges = std::ranges; using namespace std::string_view_literals; std::cout << "larger of 1 and 9999: " << ranges::max(1, 9999) << '\n' << "larger of 'a', and 'b': '" << ranges::max('a', 'b') << "'\n" << "longest of \"foo\", \"bar\", and \"hello\": \"" << ranges::max({ "foo"sv, "bar"sv, "hello"sv }, {}, &std::string_view::size) << "\"\n"; }
Output:
larger of 1 and 9999: 9999 larger of 'a', and 'b': 'b' longest of "foo", "bar", and "hello": "hello"
[edit] See also
| (C++20) |
returns the smaller of the given values (niebloid) |
| (C++20) |
returns the smaller and larger of two elements (niebloid) |
| (C++20) |
returns the largest element in a range (niebloid) |
| (C++20) |
clamps a value between a pair of boundary values (niebloid) |
| returns the greater of the given values (function template) |
