16.2 Declaring an Array

To make an array declaration, write [length] after the name being declared. This construct is valid in the declaration of a variable, a function parameter, a function value type (the value can’t be an array, but it can be a pointer to one), a structure field, or a union alternative.

The surrounding declaration specifies the element type of the array; that can be any type of data, but not void or a function type. For instance,

double a[5];

declares a as an array of 5 doubles.

struct foo bstruct[length];

declares bstruct as an array of length objects of type struct foo. A variable array size like this is allowed when the array is not file-scope.

Other declaration constructs can nest within the array declaration construct. For instance:

struct foo *b[length];

declares b as an array of length pointers to struct foo. This shows that the length need not be a constant (see Arrays of Variable Length).

double (*c)[5];

declares c as a pointer to an array of 5 doubles, and

char *(*f (int))[5];

declares f as a function taking an int argument and returning a pointer to an array of 5 strings (pointers to chars).

double aa[5][10];

declares aa as an array of 5 elements, each of which is an array of 10 doubles. This shows how to declare a multidimensional array in C (see Multidimensional Arrays).

All these declarations specify the array’s length, which is needed in these cases in order to allocate storage for the array.