std::max - cppreference.com

template< class T >
const T& max( const T& a, const T& b );

template< class T, class Compare >
const T& max( const T& a, const T& b, Compare comp );

template< class T >
T max( std::initializer_list<T> ilist );

template< class T, class Compare >
T max( std::initializer_list<T> ilist, Compare comp );

Returns the greater of the given values.

1,2) Returns the greater of a and b.

1) Uses operator< to compare the values.

2) Use the comparison function comp to compare the values.

3,4) Returns 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.

4) Use the comparison function comp to compare the values.

Parameters

Return value

1,2) The greater of a and b. If they are equivalent, returns a.

3,4) The greatest value in ilist. If several values are equivalent to the greatest, returns the leftmost one.

Complexity

1) Exactly one comparison using operator<.

2) Exactly one application of the comparison function comp.

3,4) Given N as ilist.size():

3) Exactly N-1 comparisons using operator<.

4) Exactly N-1 applications of the comparison function comp.

Possible implementation

template<class T> 
const T& max(const T& a, const T& b)
{
    return (a < b) ? b : a;
}

template<class T, class Compare> 
const T& max(const T& a, const T& b, Compare comp)
{
    return (comp(a, b)) ? b : a;
}

template<class T>
T max(std::initializer_list<T> ilist)
{
    return *std::max_element(ilist.begin(), ilist.end());
}

template<class T, class Compare>
T max(std::initializer_list<T> ilist, Compare comp)
{
    return *std::max_element(ilist.begin(), ilist.end(), comp);
}

Notes

Capturing the result of std::max by reference produces a dangling reference if one of the parameters is a temporary and that parameter is returned:

int n = -1;
const int& r = std::max(n + 2, n * 2); // r is dangling

Example

#include <algorithm>
#include <iomanip>
#include <iostream>
#include <string_view>

int main()
{
    auto longest = [](const std::string_view s1, const std::string_view s2)
                   {
                       return s1.size() < s2.size();
                   };
    
    std::cout << "Larger of 69 and 96 is " << std::max(69, 96) << "\n"
                 "Larger of 'q' and 'p' is '" << std::max('q', 'p') << "'\n"
                 "Largest of 010, 10, 0X10, and 0B10 is "
              << std::max({010, 10, 0X10, 0B10}) << '\n'
              << R"(Longest of "long", "short", and "int" is )"
              << std::quoted(std::max({"long", "short", "int"}, longest)) << '\n';
}

Larger of 69 and 96 is 96
Larger of 'q' and 'p' is 'q'
Largest of 010, 10, 0X10, and 0B10 is 16
Longest of "long", "short", and "int" is "short"

Defect reports

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

See also