NAME

std::minmax - std::minmax

Synopsis

Defined in header <algorithm>
template< class T > (since
std::pair<const T&,const T&> minmax( const C++11)
T& a, const T& b ); (until
C++14)
template< class T > (since
constexpr std::pair<const T&,const T&> C++14)
minmax( const T& a, const T& b );
template< class T, class Compare >
(since
std::pair<const T&,const T&> minmax( const C++11)
T& a, const T& b, (until
C++14)
Compare comp );
template< class T, class Compare >

constexpr std::pair<const T&,const T&> (since
minmax( const T& a, const T& b, (1) C++14)

Compare comp );
template< class T > (since
std::pair<T,T> minmax( (2) C++11)
std::initializer_list<T> ilist); (until
C++14)
template< class T > (since
constexpr std::pair<T,T> minmax( C++14)
std::initializer_list<T> ilist);
template< class T, class Compare > (3) (since
std::pair<T,T> minmax( C++11)
std::initializer_list<T> ilist, Compare comp (until
); (4) C++14)
template< class T, class Compare >
constexpr std::pair<T,T> minmax( (since
std::initializer_list<T> ilist, Compare comp C++14)
);

Returns the lowest and the greatest of the given values.

1-2) Returns references to the smaller and the greater of a and b.
3-4) Returns the smallest and the greatest of the values in initializer list ilist.

The (1,3) versions use operator< to compare the values, whereas the (2,4) versions
use the given comparison function comp.

Parameters

a, b - the values to compare
ilist - initializer list with the values to compare
comparison function object (i.e. an object that satisfies the requirements
of Compare) which returns true if the first argument is less than the
second.

The signature of the comparison function should be equivalent to the
following:

bool cmp(const Type1 &a, const Type2 &b);
comp -
While the signature does not need to have const &, the function must not
modify the objects passed to it and must be able to accept all values of
type (possibly const) Type1 and Type2 regardless of value category (thus,
Type1 & is not allowed
, nor is Type1 unless for Type1 a move is equivalent to a copy
(since C++11)).
The types Type1 and Type2 must be such that an object of type T can be
implicitly converted to both of them.

Type requirements

-
T must meet the requirements of LessThanComparable in order to use overloads (1,3).
-
T must meet the requirements of CopyConstructible in order to use overloads (3,4).

Return value

1-2) Returns the result of std::pair<const T&, const T&>(a, b) if a<b or if a is
equivalent to b. Returns the result of std::pair<const T&, const T&>(b, a) if b<a.
3-4) A pair with the smallest value in ilist as the first element and the greatest
as the second. If several elements are equivalent to the smallest, the leftmost such
element is returned. If several elements are equivalent to the largest, the
rightmost such element is returned.

Complexity

1-2) Exactly one comparison
3-4) At most ilist.size() * 3 / 2 comparisons

Possible implementation

First version

template<class T>
constexpr std::pair<const T&, const T&> minmax( const T& a, const T& b )
{
return (b < a) ? std::pair<const T&, const T&>(b, a)
: std::pair<const T&, const T&>(a, b);
}

Second version

template<class T, class Compare>
constexpr std::pair<const T&, const T&> minmax( const T& a, const T& b, Compare comp )
{
return comp(b, a) ? std::pair<const T&, const T&>(b, a)
: std::pair<const T&, const T&>(a, b);
}
Third version
template< class T >
constexpr std::pair<T, T> minmax( std::initializer_list<T> ilist )
{
auto p = std::minmax_element(ilist.begin(), ilist.end());
return std::pair(*p.first, *p.second);
}
Fourth version
template< class T, class Compare >
constexpr std::pair<T, T> minmax( std::initializer_list<T> ilist, Compare comp )
{
auto p = std::minmax_element(ilist.begin(), ilist.end(), comp);
return std::pair(*p.first, *p.second);
}

Notes

For overloads (1,2), 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::minmax(n, n+1);
int m = p.first; // ok
int x = p.second; // undefined behavior

// Note that structured bindings have the same issue
auto [mm, xx] = std::minmax(n, n+1);
xx; // undefined behavior

Example

// Run this code

#include <algorithm>
#include <iostream>
#include <vector>
#include <cstdlib>
#include <ctime>

int main()
{
std::vector<int> v {3, 1, 4, 1, 5, 9, 2, 6};
std::srand(std::time(0));
std::pair<int, int> bounds = std::minmax(std::rand() % v.size(),
std::rand() % v.size());

std::cout << "v[" << bounds.first << "," << bounds.second << "]: ";
for (int i = bounds.first; i < bounds.second; ++i) {
std::cout << v[i] << ' ';
}
std::cout << '\n';
}

Possible output:

v[2,7]: 4 1 5 9 2