std::minmax

 

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Technical Specifications

 

Algorithm library

Execution policies (C++17)
is_execution_policy	sequentialparpar_vec	sequential_execution_policyparallel_execution_policyparallel_vector_execution_policy
Non-modifying sequence operations
all_ofany_ofnone_of (C++11)(C++11)(C++11) for_each for_each_n (C++17)	countcount_if mismatch equal lexicographical_compare	findfind_iffind_if_not (C++11) find_end find_first_of	adjacent_find search search_n
Modifying sequence operations
copycopy_if (C++11) copy_n (C++11) copy_backward move (C++11) move_backward (C++11) transform	fill fill_n generate generate_n swap iter_swap swap_ranges sample (C++17)	removeremove_if replacereplace_if reverse rotate unique random_shuffle (until C++17)	remove_copyremove_copy_if replace_copyreplace_copy_if reverse_copy rotate_copy unique_copy shuffle (C++11)
Operations on uninitialized storage
uninitialized_copy	uninitialized_copy_n	uninitialized_fill	uninitialized_fill_n
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is_partitioned (C++11) partition_point (C++11)	partition partition_copy (C++11)	stable_partition
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is_sorted (C++11) is_sorted_until (C++11)	sort stable_sort	partial_sort partial_sort_copy	nth_element
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lower_bound	upper_bound	binary_search	equal_range
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merge inplace_merge	set_difference set_intersection	set_symmetric_difference set_union	includes
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is_heap (C++11) is_heap_until (C++11)	make_heap sort_heap	push_heap pop_heap
Minimum/maximum operations
max max_element	min min_element	minmax (C++11) minmax_element (C++11)	clamp (C++17)
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C library
qsort	bsearch

 

Defined in header <algorithm>
	(1)
template< class T > std::pair<const T&,const T&> minmax( const T& a, const T& b );			(since C++11) (until C++14)
template< class T > constexpr std::pair<const T&,const T&> minmax( const T& a, const T& b );			(since C++14)
		(2)
template< class T, class Compare > std::pair<const T&,const T&> minmax( const T& a, const T& b,                                      Compare comp );				(since C++11) (until C++14)
template< class T, class Compare > constexpr std::pair<const T&,const T&> minmax( const T& a, const T& b,                                                Compare comp );				(since C++14)
			(3)
template< class T > std::pair<T,T> minmax( std::initializer_list<T> ilist);					(since C++11) (until C++14)
template< class T > constexpr std::pair<T,T> minmax( std::initializer_list<T> ilist);					(since C++14)
				(4)
template< class T, class Compare > std::pair<T,T> minmax( std::initializer_list<T> ilist, Compare comp );						(since C++11) (until C++14)
template< class T, class Compare > constexpr std::pair<T,T> minmax( std::initializer_list<T> ilist, Compare comp );						(since 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
comp	-	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); The signature does not need to have const &, but the function object must not modify the objects passed to it. 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> 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> 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 > std::pair<T, T> minmax( std::initializer_list<T> ilist ) { auto p = std::minmax_element(ilist.begin(), ilist.end()); return std::make_pair(*p.first, *p.second); }
Fourth version
template< class T, class Compare > std::pair<T, T> minmax( std::initializer_list<T> ilist, Compare comp ) { auto p = std::minmax_element(ilist.begin(), ilist.end(), comp); return std::make_pair(*p.first, *p.second); }

Notes

For overloads (1,2), if one of the parameters is an rvalue, 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

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

See also

min	returns the smaller of the given values (function template)
max	returns the greater of the given values (function template)
minmax_element (C++11)	returns the smallest and the largest elements in a range (function template)