table of contents
std::ranges::max(3) | C++ Standard Libary | std::ranges::max(3) |
NAME¶
std::ranges::max - std::ranges::max
Synopsis¶
Defined in header <algorithm>
Call signature
template< class T, class Proj = std::identity,
std::indirect_strict_weak_order< (since
std::projected<const T*, Proj>> Comp = ranges::less > C++20)
constexpr const T& max( const T& a, const T& b, Comp comp = {},
Proj proj =
{} );
template< std::copyable T, class Proj = std::identity,
std::indirect_strict_weak_order< (since
std::projected<const T*, Proj>> Comp = ranges::less > C++20)
constexpr const T max( std::initializer_list<T> r, Comp comp = {}, Proj
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 > (since
requires std::indirectly_copyable_storable<ranges::iterator_t<R>,
C++20)
ranges::range_value_t<R>*>
constexpr ranges::range_value_t<R> max( R&& r, Comp comp = {},
Proj proj =
{} );
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 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¶
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
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.
Complexity¶
1) Exactly one comparison.
2-3) Exactly ranges::distance(r) - 1 comparisons.
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;
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
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"
See also¶
ranges::min returns the smaller of the given values
(C++20) (niebloid)
ranges::minmax returns the smaller and larger of two elements
(C++20) (niebloid)
ranges::max_element returns the largest element in a range
(C++20) (niebloid)
ranges::clamp clamps a value between a pair of boundary values
(C++20) (niebloid)
max returns the greater of the given values
(function template)
2022.07.31 | http://cppreference.com |