Variable length array in the middle of struct - why this C code is valid for gcc

Question

There is some strange code using VLA (Variable Length Arrays) which is treated as Valid C (C99, C11) by gcc 4.6:

$ cat a.c
int main(int argc,char**argv)
{
           


        

Answer 1

The standard is pretty clear that VLAs are not allowed in a struct:

6.7.2.1 Structure and union specifiers

9 - A member of a structure or union may have any complete object type other than a variably modified type. [...]

Variably modified types are (as you might expect) those derived from a variable length array (e.g. by adding array dimensions or cv qualifiers):

6.7.6 Declarators

3 - [...] If, in the nested sequence of declarators in a full declarator, there is a declarator specifying a variable length array type, the type specified by the full declarator is said to be variably modified. Furthermore, any type derived by declarator type derivation from a variably modified type is itself variably modified.