A.8.6.2 Array Declarators
In a declaration T D where D has the form
- D1 [constant-expressionopt]
and the type of the identifier in the declaration T D1 is type-modifier T, the type of the identifier of D is type-modifier array of T. If the constant-expression is present, it must have integral type, and value greater than 0. If the constant expression specifying the bound is missing, the array has an incomplete type.
An array may be constructed from an arithmetic type, from a pointer, from a structure or union, or from another array (to generate a multi-dimensional array). Any type from which an array is constructed must be complete; it must not be an array of structure of incomplete type. This implies that for a multi-dimensional array, only the first dimension may be missing. The type of an object of incomplete aray type is completed by another, complete, declaration for the object (Par.A.10.2), or by initializing it (Par.A.8.7). For example,
- float fa[17], *afp[17];
declares an array of float numbers and an array of pointers to float numbers. Also,
- static int x3d[3][5][7];
declares a static three-dimensional array of integers, with rank 3 X 5 X 7. In complete detail, x3d is an array of three items: each item is an array of five arrays; each of the latter arrays is an array of seven integers. Any of the expressions x3d, x3d[i], x3d[i][j], x3d[i][j][k] may reasonably appear in an expression. The first three have type array,, the last has type int. More specifically, x3d[i][j] is an array of 7 integers, and x3d[i] is an array of 5 arrays of 7 integers. The array subscripting operation is defined so that E1[E2] is identical to *(E1+E2). Therefore, despite its asymmetric appearance, subscripting is a commutative operation. Because of the conversion rules that apply to + and to arrays (Pars.A6.6, A.7.1, A.7.7), if E1 is an array and E2 an integer, then E1[E2] refers to the E2-th member of E1. In the example, x3d[i][j][k] is equivalent to *(x3d[i][j] + k). The first subexpression x3d[i][j] is converted by Par.A.7.1 to type pointer to array of integers,