NAME¶

std::minmax - std::minmax

Synopsis¶

Defined in header <algorithm>
template< class T > (since C++11)
std::pair<const T&, const T&> minmax( const T& a, const (1) (constexpr since C++14)
T& b );
template< class T, class Compare >

std::pair<const T&, const T&> minmax( const T& a, const (2) (since C++11)
T& b, (constexpr since C++14)

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

Compare comp );

Returns the lowest and the greatest of the given values.

1,2) Returns references to the smaller and the greater of a and b.
1) Uses operator< to compare the values.
If T is not LessThanComparable, the behavior is undefined.
2) Use the comparison function comp to compare the values.
3,4) Returns the smallest and the greatest of the values in initializer list ilist.
If ilist.size() is zero, or T is not CopyConstructible, the behavior is undefined.
3) Uses operator< to compare the values.
If T is not LessThanComparable, the behavior is undefined.
4) Use the comparison function comp to compare the values.

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.

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) Exactly one comparison using operator<.
2) Exactly one application of the comparison function comp.
3,4) Given \(\scriptsize N\)N as ilist.size():
3) At most \(\scriptsize \frac{3N}{2}\)

3N
2

comparisons using operator<.
4) At most \(\scriptsize \frac{3N}{2}\)

3N
2

applications of the comparison function comp.

Possible implementation¶

minmax (1)
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);
}
minmax (2)
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);
}
minmax (3)
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);
}
minmax (4)
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 <cstdlib>
#include <ctime>
#include <iostream>
#include <vector>

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

See also¶

min returns the smaller of the given values
(function template)
max returns the greater of the given values
(function template)
minmax_element returns the smallest and the largest elements in a range
(C++11) (function template)
ranges::minmax returns the smaller and larger of two elements
(C++20) (niebloid)