Originally Posted by C Standard, 1999 edition, section 6.7.5.2 paragraph 10
All declarations of variably modified (VM) types have to be at either block scope or function prototype scope. Array objects declared with the static or extern storage-class specifier cannot have a variable length array (VLA) type. However, an object declared with the static storageclass specifier can have a VM type (that is, a pointer to a VLA type). Finally, all identifiers declared with a VM type have to be ordinary identifiers and cannot, therefore, be members of structures or unions.