std::max(3)

NAME
std::max - std::max

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

Example
// Run this code
 #include <algorithm>
 #include <iostream>
 #include <string_view>
 int main()
 {
     std::cout << "larger of 1 and 9999 is " << std::max(1, 9999) << '\n'
               << "larger of 'a', and 'b' is '" << std::max('a', 'b') << "'\n"
               << "largest of 1, 10, 50, and 200 is " << std::max({1, 10, 50, 200}) << '\n'
               << "longest of \"foo\", \"bar\", and \"hello\" is \""
               << std::max({ "foo", "bar", "hello" },
                        [](const std::string_view s1, const std::string_view s2) {
                        return s1.size() < s2.size();
                        }) << "\"\n";
 }

Output:
 larger of 1 and 9999 is 9999
 larger of 'a', and 'b' is 'b'
 largest of 1, 10, 50, and 200 is 200
 longest of "foo", "bar", and "hello" is "hello"

See also
   min returns the smaller of the given values
               (function template)
   minmax returns the smaller and larger of two elements
   (C++11) (function template)
   max_element returns the largest element in a range
               (function template)
   clamp clamps a value between a pair of boundary values
   (C++17) (function template)
   ranges::max returns the greater of the given values
   (C++20) (niebloid)