Std::max (3) Linux Manual Page

std::max – std::max

Synopsis

Defined in header<algorithm>

    template <class T>
    (until C++ 14)

        const T &max(const T &a, const T &b);

template <class T>
(since C++ 14)

    constexpr const T &max(const T &a, const T &b);

template <class T, class Compare>
(until C++ 14)

    const T &max(const T &a, const T &b, Compare comp);

template <class T, class Compare>
(since C++ 14)

    constexpr const T &max(const T &a, const T &b, Compare comp);
(1)

    template <class T>
    (since C++ 11)

        T max(std::initializer_list<T> ilist);
(2)(until C++ 14)

    template <class T>
    (since C++ 14)

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

    template <class T, class Compare>
    (since C++ 11)

        T max(std::initializer_list<T> ilist, Compare comp);
(4)(until C++ 14)

    template <class T, class Compare>
    (since C++ 14)

        constexpr 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.
3-4) Returns the greatest of the values in initializer list ilist.
The (1,3) versions use operator< to compare the values, 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
        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);
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.

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) 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

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

Possible implementation

First version

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

Second version

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

Third version

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

Fourth version

  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 if one of the parameters is rvalue produces a dangling reference if that parameter is returned:

int n = 1;

const int &r = std::max(n - 1, n + 1);

// r is dangling

Example

// Run this code

#include <algorithm>

#include <iostream>

#include <string>
int main()

{
    std::cout << "larger of 1 and 9999: " << std::max(1, 9999) << '\n'
              << "larger of 'a', and 'b': " << std::max('a', 'b') << '\n'
              << "longest of \"foo\", \"bar\", and \"hello\": " << std::max({"foo", "bar", "hello"}, [](const std::string &s1, const std::string &s2) {
                     return s1.size() < s2.size();
                 })
              << '\n';
}

Output:

  larger of 1 and 9999: 9999
  larger of ‘a’, and ‘b’: b
  longest of "foo", "bar", and "hello": hello

std::max (3) Linux Manual Page