Is Incomplete array type guaranteed to be able to store one element?

Question

Incomplete array types are used in the famous Struct hack and they are allowed since c99 standard. prior to c99 standard these were not allowed. I was looking at the standard and I am unable to conclude:

Are Incomplete array types allowed outside a structure?(All references I found in the standard C99: 6.7.2.1.15 talk about it as the last element in the structure).

So is the following program allowed to compile as per the standard?

int array[];
int main(){return 0;}

Second part of my questions is, If this is allowed is array guaranteed to be able to store atleast one element of they type int.

Answer 1

is the following program allowed to compile as per the standard?

Yes, as per:

(C99, 6.9.2p5) "EXAMPLE 2 If at the end of the translation unit containing int i[]; the array i still has incomplete type, the implicit initializer causes it to have one element, which is set to zero on program startup."

So

int array[];
int main(){return 0;}

is valid and equivalent to:

int array[1];
int main(){return 0;}

Note that it is OK only if array has (like above) external linkage as:

(C99, 6.9.2p3) "If the declaration of an identifier for an object is a tentative definition and has internal linkage, the declared type shall not be an incomplete type."