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    std::minmax

    From cppreference.com
     
    C++
     
    Algorithm library
    Constrained algorithms and algorithms on ranges (C++20)
    Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
    Non-modifying sequence operations    
    Batch operations
    (C++17)
    Search operations
    Modifying sequence operations
    Copy operations
    (C++11)
    (C++11)
    (C++11)
    Swap operations
    Transformation operations
    Generation operations
    Removing operations
    Order-changing operations
    (until C++17)(C++11)
    (C++20)(C++20)
    Sampling operations
    (C++17)

    Sorting and related operations
    Partitioning operations
    (C++11)    
    (C++11)

    Sorting operations
    Binary search operations
    (on partitioned ranges)
    Set operations (on sorted ranges)
    Merge operations (on sorted ranges)
    Heap operations
    Minimum/maximum operations
    (C++11)
    (C++17)
    Lexicographical comparison operations
    (C++20)
    Permutation operations


     
    Defined in header <algorithm> 
    template< class T >
std::pair<const T&, const T&> minmax( const T& a, const T& b );
    		(1) (since C++11)
    (constexpr since C++14)    		 
    template< class T, class Compare >
std::pair<const T&, const T&> minmax( const T& a, const T& b,
                                      Compare comp );
    		(2) (since C++11)
    (constexpr since C++14)    		 
    template< class T >
std::pair<T, T> minmax( std::initializer_list<T> ilist );
    		(3) (since C++11)
    (constexpr since C++14)    		 
    template< class T, class Compare >
std::pair<T, T> minmax( std::initializer_list<T> ilist,
                        Compare comp );
    		(4) (since C++11)
    (constexpr since C++14)
    See More

    Returns the smallest and the greatest of the given values.

    1,2) Returns the smaller and greater of a and b in order.
    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
    comp - comparison function object (i.e. an object that satisfies the requirements of Compare) which returns true if a is less than b.

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

    bool cmp(const Type1& a, const Type2& b);

    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) A std::pair object, where:
    • The data member first holds b is b is smaller than a, or a otherwise.
    • The data member second holds a is b is smaller than a, or b otherwise.
    3,4) A std::pair object, where:
    • The data member first holds the smallest value in ilist. If there are multiple smallest values, first holds the first one of them.
    • The data member second holds the largest value in ilist. If there are multiple largest values, second holds the last one of them.

    Complexity

    1) Exactly one comparison using operator<.
    2) Exactly one application of the comparison function comp.
    3,4) Given N as ilist.size():
    3) At most
    3N
    2
     comparisons using operator<.
    4) At most
    3N
    2
     applications of the comparison function comp.

    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

    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);
}

    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

    Defect reports

    The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

    DR Applied to Behavior as published Correct behavior
    LWG 2239 C++11 T was required to be LessThanComparable for overloads (2,4) not required

    See also

    (C++20)
    		 returns the smaller and larger of two elements
    (algorithm function object)[edit]
    		returns the smaller of the given values
    (function template & algorithm function object)[edit]
    (C++20)
    		returns the greater of the given values
    (function template & algorithm function object)[edit]
    (C++20)
    (C++11)
    		 returns the smallest and the largest elements in a range
    (function template & algorithm function object)[edit]
    (C++20)