Member initializer list notation: curly braces vs parentheses

Question

Consider the following code snippet from pg. 17 \'s A Tour of C++:

class Vector {
public:
  Vector(int s) :elem{new double[s]}, sz{s} { } //construct         


        

Answer 1

The form

Vector(int s) :elem(new double[s]), sz(s) { }

is correct in all versions of C++. The one with curly-braces, like

Vector(int s) :elem{new double[s]}, sz{s} { }

was introduced into the C++ standard in 2011, and is invalid in older standards.

In the context you ask about, there is no difference. However, there are other language and library features, also introduced into the 2011 standard, that rely on the second form and don't work with the first.

There are no other ways of initialising members of bases in initialiser lists of constructors. It is possible to assign to members in the body of constructors, but that is not initialiser syntax.