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std::ranges::max

From cppreference.com
< cpp‎ | algorithm‎ | ranges
 
 
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
Batch operations
(C++17)
Search operations
(C++11)                (C++11)(C++11)

Modifying sequence operations
Copy operations
(C++11)
(C++11)
Swap operations
Transformation operations
Generation operations
Removing operations
Order-changing operations
(until C++17)(C++11)
(C++20)(C++20)
Sampling operations
(C++17)

Sorting and related operations
Partitioning operations
Sorting operations
Binary search operations
(on partitioned ranges)
Set operations (on sorted ranges)
Merge operations (on sorted ranges)
Heap operations
Minimum/maximum operations
(C++11)
(C++17)
Lexicographical comparison operations
Permutation operations
C library
Numeric operations
Operations on uninitialized memory
 
Constrained algorithms
Non-modifying sequence operations
Modifying sequence operations
Partitioning operations
Sorting operations
Binary search operations (on sorted ranges)
Set operations (on sorted ranges)
Heap operations
Minimum/maximum operations
ranges::max
Permutation operations
Numeric operations
Fold operations
Operations on uninitialized storage
Random number generation
Return types
 
Defined in header <algorithm>
Call signature
template< class T, class Proj = std::identity,

          std::indirect_strict_weak_order<
              std::projected<const T*, Proj>> Comp = ranges::less >
constexpr const T&

    max( const T& a, const T& b, Comp comp = {}, Proj proj = {} );
(1) (since C++20)
template< std::copyable T, class Proj = std::identity,

          std::indirect_strict_weak_order<
              std::projected<const T*, Proj>> Comp = ranges::less >
constexpr T

    max( std::initializer_list<T> r, Comp comp = {}, Proj proj = {} );
(2) (since C++20)
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>

    max( R&& r, Comp comp = {}, Proj proj = {} );
(3) (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:

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
    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 + 2, n * 2); // r is dangling

[edit] Example

#include <algorithm>
#include <iostream>
#include <string>
 
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
(niebloid)[edit]
returns the smaller and larger of two elements
(niebloid)[edit]
returns the largest element in a range
(niebloid)[edit]
clamps a value between a pair of boundary values
(niebloid)[edit]
returns the greater of the given values
(function template) [edit]