c++ - What's the point of g++ -Wreorder?

Question

The g++ -Wall option includes -Wreorder. What this option does is described below. It is not obvious to me why somebody would care (especially enough to turn this on by default in -Wall).

-Wreorder (C++ only)
  Warn when the order of member initializers given in the code does not
  match the order in which they must be executed.  For instance:

    struct A {
      int i;
      int j;
      A(): j (0), i (1) { }
    };

  The compiler will rearrange the member initializers for i and j to
  match the declaration order of the members, emit-ting a warning to that
  effect.  This warning is enabled by -Wall.

Answer 1

Consider:

struct A {
    int i;
    int j;
    A() : j(0), i(j) { }
};

Now i is initialized to some unknown value, not zero.

Alternatively, the initialization of i may have some side effects for which the order is important. E.g.

A(int n) : j(n++), i(n++) { }