Question

I was wondering about an initialization of the following form:

int  array[] = {
v - 1,
array[0] + 1
} ;

In the initialization of the second element, the value of the first is used, but the entire array is not yet initialized. This happens to compile with g++, but I was unsure whether this is actually portable and a well defined construct?

Answer 1

See 3.3.2 Point of declaration:

The point of declaration for a name is immediately after its complete declarator (Clause 8) and before its
initializer (if any), except as noted below. [ Example:

int x = 12;
{ int x = x; }

Here the second x is initialized with its own (indeterminate) value. —end example ]

So you are referring to the array correctly, its name is known after the =.

Then, 8.5.1 Aggregates:

An aggregate is an array or a class […]

17: The full-expressions in an initializer-clause are evaluated in the order in which they appear.

However, I see no reference to when the evaluated values are actually written into the array, so I wouldn’t rely on this and would even go so far to declare your code as not well defined.