std::max (3) - Linux Manuals

std::max: std::max

NAME

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