Question

What, exactly, is numbers in the following declaration, if it is not an address constant?

int main() {
    int numbers[3] = {1,2,3};
    return 0;
}

Disassembling the program shows that 1, 2, and 3 are dynamically placed on the local stack space, rather than the whole array being treated as a constant. Hence, {1,2,3} does not have static storage duration, so numbers is not an address constant, as per the C99 spec.

C99, Section 6.6.9: “An address constant is a null pointer, a pointer to an lvalue designating an object of static storage duration, or a pointer to a function designator…”

However, adding the line numbers++ after the declaration causes the following compile error in GCC 4.1.2:

error: invalid lvalue in increment

So it is constant, but isn’t an address constant. Does anybody know the official name of this type of constant in C99 (or similar)?

Answer 1

numbers is a non-constant, automatic, array variable of the function main.

Because it is automatic and non-constant it can not have static storage.

because it is an array variable (and not you’ll notice a pointer) it can not be incremented.

Note that you can do

int main() {
    int numbers[3] = {1,2,3};
    int *n = numbers+1;
    n++;
    return 0;
}