std::ranges::minmax, std::ranges::minmax_result
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
<std::projected<const T*, Proj>> Comp = ranges::less >
constexpr ranges::minmax_result<const T&>
minmax( const T& a, const T& b, Comp comp = {}, Proj proj = {} );
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(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 ranges::minmax_result<T>
minmax( std::initializer_list<T> r, Comp comp = {}, Proj proj = {} );
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(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::minmax_result<ranges::range_value_t<R>>
minmax( R&& r, Comp comp = {}, Proj proj = {} );
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(3) | (since C++20) |
template< /*execution-policy*/ Ep, /*sized-random-access-range*/ R,
class Proj = 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>*>
ranges::minmax_result<ranges::range_value_t<R>>
minmax( Ep&& policy, R&& r, Comp comp = {}, Proj proj = {} );
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(4) | (since C++26) |
| Helper types |
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template< class T >
using minmax_result = ranges::min_max_result<T>;
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(5) | (since C++20) |
For the definition of /*execution-policy*/, see this page; for the definition of /*sized-random-access-range*/, see this page.
Returns the smallest and the greatest of the given values (projected by proj), the projected values are compared using comp.
1) Returns the smaller and greater of
a and b in order.2-4) Returns the first smallest value and the first largest value in the initializer list or target range
r. If
ranges::distance(r) is zero, the behavior is undefined.4) Same as (3), but executed according to
policy.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.
Parameters
| a, b | - | the values to compare |
| r | - | the range of values to compare |
| comp | - | the comparator to be applied to the (projected) elements |
| proj | - | the projection to be applied to the elements |
| policy | - | the execution policy to use |
Return value
1) A
ranges::minmax_result object, where:
2-4) A
ranges::minmax_result object, where:
Complexity
1) Exactly one application of
comp, and two applications of proj.2-4) Given N as
ranges::distance(r):2,3) At most
applications of
| 3N |
| 2 |
comp, and twice as many applications of proj.4) 𝓞(N) applications of
comp, and twice as many applications of proj.Exceptions
4) During the execution process:
- If the temporary memory resources required for parallelization are not available, std::bad_alloc is thrown.
- If an uncaught exception is thrown while accessing objects via an algorithm argument, the behavior is determined by the execution policy (for standard policies, std::terminate is invoked).
Notes
For overload (1), if one of the parameters is a temporary, the reference returned becomes a dangling reference at the end of the full expression that contains the call to minmax:
int n = 1;
auto p = std::ranges::minmax(n, n + 1);
int m = p.min; // ok
int x = p.max; // undefined behavior
// Note that structured bindings have the same issue
auto [mm, xx] = std::ranges::minmax(n, n + 1);
xx; // undefined behavior
Possible implementation
struct minmax_fn
{
template<class T, class Proj = std::identity,
std::indirect_strict_weak_order
<std::projected<const T*, Proj>> Comp = ranges::less>
constexpr ranges::minmax_result<const T&>
operator()(const T& a, const T& b, Comp comp = {}, Proj proj = {}) const
{
if (std::invoke(comp, std::invoke(proj, b), std::invoke(proj, a)))
return {b, a};
return {a, b};
}
template<std::copyable T, class Proj = std::identity,
std::indirect_strict_weak_order
<std::projected<const T*, Proj>> Comp = ranges::less>
constexpr ranges::minmax_result<T>
operator()(std::initializer_list<T> r, Comp comp = {}, Proj proj = {}) const
{
auto result = ranges::minmax_element(r, std::ref(comp), std::ref(proj));
return {*result.min, *result.max};
}
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::minmax_result<ranges::range_value_t<R>>
operator()(R&& r, Comp comp = {}, Proj proj = {}) const
{
auto first = ranges::begin(r);
const auto last = ranges::end(r);
auto min = static_cast<range_value_t<R>>(*first), max = min;
while (++first != last)
{
auto x = static_cast<range_value_t<R>>(*first);
if (++first == last)
{
if (std::invoke(comp, std::invoke(proj, x),
std::invoke(proj, min)))
min = x;
else if (!std::invoke(comp, std::invoke(proj, x),
std::invoke(proj, max)))
max = x;
break;
}
if (std::invoke(comp, std::invoke(proj, *first),
std::invoke(proj, x)))
{
if (std::invoke(comp, std::invoke(proj, *first),
std::invoke(proj, min)))
min = *first;
if (!std::invoke(comp, std::invoke(proj, x),
std::invoke(proj, max)))
max = x;
}
else
{
if (std::invoke(comp, std::invoke(proj, x),
std::invoke(proj, min)))
min = x;
if (!std::invoke(comp, std::invoke(proj, *first),
std::invoke(proj, max)))
max = *first;
}
}
return {min, max};
}
};
inline constexpr minmax_fn minmax;
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Example
Run this code
#include <algorithm>
#include <array>
#include <iostream>
#include <random>
int main()
{
namespace ranges = std::ranges;
constexpr std::array v{3, 1, 4, 1, 5, 9, 2, 6, 5};
std::random_device rd;
std::mt19937_64 generator(rd());
std::uniform_int_distribution<> distribution(0, ranges::distance(v)); // [0..9]
// auto bounds = ranges::minmax(distribution(generator), distribution(generator));
// UB: dangling references: bounds.min and bounds.max have the type “const int&”.
const int x1 = distribution(generator);
const int x2 = distribution(generator);
auto bounds = ranges::minmax(x1, x2); // OK: got references to lvalues x1 and x2
std::cout << "v[" << bounds.min << ":" << bounds.max << "]: ";
for (int i = bounds.min; i < bounds.max; ++i)
std::cout << v[i] << ' ';
std::cout << '\n';
auto [min, max] = ranges::minmax(v);
std::cout << "smallest: " << min << ", " << "largest: " << max << '\n';
}
Possible output:
v[3:9]: 1 5 9 2 6 5
smallest: 1, largest: 9
See also
(C++11) |
returns the smaller and larger of two elements (function template) |
(C++20) |
returns the smaller of the given values (algorithm function object) |
(C++20) |
returns the greater of the given values (algorithm function object) |
(C++20) |
returns the smallest and the largest elements in a range (algorithm function object) |
(C++20) |
clamps a value between a pair of boundary values (algorithm function object) |