C++ max function

Question

Not sure about this one, Virtual Studio:

Works: max({SPANX,SPANY,SPANZ});

Does not work: max(SPANX,SPANY,SPANZ);, generates a "build" error

Why does one need the delimiters ({ )}; ?? Sid Kraft

Answer 1

std::max is overloaded for:

template<class Type>
constexpr Type& max(const Type& left, const Type& right);

template<class Type>
constexpr Type& max(initializer_list<Type> ilist);

So there are two relevant forms:

1. Two arguments: max(a, b)
2. An initializer_list: max({a, b, c, ...})

max(SPANX, SPANY, SPANZ); tries to call a function taking three separate parameters, but there is no std::max overload that takes three arguments, so the compiler reports a build error.

max({SPANX, SPANY, SPANZ}); passes a single argument of type std::initializer_list<T> (constructed from the braced list), which matches the max(initializer_list<Type>) overload. That overload is specifically designed to take an arbitrary number of values and return the largest.

The braces { ... } are therefore required to form an initializer_list so that the correct overload can be called when using more than two values.

If only two values are needed, both forms are valid:

max(SPANX, SPANY);        // two-argument overload
max({SPANX, SPANY});      // initializer_list overload

But for three or more values, the initializer_list form is required.

---

References:

• <algorithm> functions