std::max() algorithm

od C++14

// (1)
template< class T >
constexpr const T& max( const T& a, const T& b );

// (2)
template< class T, class Compare >
constexpr const T& max( const T& a, const T& b, Compare comp );

// (3)
template< class T >
constexpr T max( std::initializer_list<T> ilist );

// (4)
template< class T, class Compare >
constexpr T max( std::initializer_list<T> ilist, Compare comp );

od C++11

// (1)
template< class T >
const T& max( const T& a, const T& b );

// (2)
template< class T, class Compare >
const T& max( const T& a, const T& b, Compare comp );

// (3)
template< class T >
T max( std::initializer_list<T> ilist );

// (4)
template< class T, class Compare >
T max( std::initializer_list<T> ilist, Compare comp );

do C++11

// (1)
template< class T >
const T& max( const T& a, const T& b );

// (2)
template< class T, class Compare >
const T& max( const T& a, const T& b, Compare comp );

Returns the greater of the given values.

• (1 - 2) Returns the greater of a and b.
• (3 - 4) Returns the greatest of the values in initializer list ilist.

Parameters

a b	The values to compare.
ilist	Initializer list with the values to compare.
cmp	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 (od 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

• (1, 3):

  T	LessThanComparable

• (3 - 4):

  T	CopyConstructible

Return value

• (1 - 2) The greater of a and b, according to the projection. If they are equivalent, returns a.
• (3 - 4) The greatest value in ilist. If several values are equivalent to the greatest, returns the leftmost such value.

Complexity

• (1 - 2) Exactly one comparison.
• (3 - 4) Exactly ilist.size() - 1 comparisons.

Exceptions

(none)

Possible implementation

max (1)

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

max (2)

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

max (3)

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

max (4)

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

Notes

Undefined Behavior

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 - 1, n + 1); // r is dangling

Examples

Main.cpp

#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';
}

Output

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"