std::ranges::max - cppreference.com (original) (raw)

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 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

• 1 Parameters
• 2 Return value
• 3 Complexity
• 4 Possible implementation
• 5 Notes
• 6 Example
• 7 See also

[edit] Parameters

[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.

[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 T operator()(std::initializer_list 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, Proj>> Comp = ranges::less> requires std::indirectly_copyable_storable<ranges::iterator_t, ranges::range_value_t> constexpr ranges::range_value_t operator()(R&& r, Comp comp = {}, Proj proj = {}) const { using V = ranges::range_value_t; if constexpr (ranges::forward_range) return static_cast(*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 + 2, n * 2); // r is dangling

[edit] Example

#include #include #include   static_assert(std::ranges::max({0B10, 0X10, 010, 10}) == 16); // overload (2)   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

| | returns the smaller of the given values(algorithm function object)[edit] | | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | returns the smaller and larger of two elements(algorithm function object)[edit] | | | returns the largest element in a range(algorithm function object)[edit] | | | clamps a value between a pair of boundary values(algorithm function object)[edit] | | | returns the greater of the given values (function template) [edit] |