std::max Returns Wrong Value

C++ STL’s ‘std::max returns the first argument when the two arguments are equivalent, while it should returns the second argument.

This makes a different when two arguments are equivalent in terms of oprator== but not strictly equal (which is a coding anti-pattern, but such code exists).

For example, in the below code, we can easily have two person with the same name but different ages.

struct Person {
  std::string name;
  int age;
 
  friend bool operator==(const Person& lhs, const Person& rhs) {
    return lhs.name == rhs.name;
  }
};

If std::max returns the second argument in this case, it can preserve a few useful properties:

• the pair (min(x,y), max(x,y)) is either (x,y) or (y,x),
• if x and y are distinct, then min(x,y) and max(x,y) are distinct,
• the function that maps (x,y) to (min(x,y), max(x,y)) is a stable sorting function for sets of two elements.