Zero-sized arrays

The size of an array is the product of the extents of each dimension; if any extent is zero then the array has no size and is known as a zero-sized array. Any of the arrays described in this chapter may be zero-sized apart from assumed-sized arrays which have no specified size. This concept of a zero-sized arrays is important if a number of algorithms are to be expressed naturally.

Note that while zero-sized arrays have no elements, they do still have a shape and this is important when they are used in array expressions which are described below. Operations involving zero-sized arrays are generally null operations.

Following are some examples of zero-sized arrays:

INTEGER, PARAMETER :: cases = 0

REAL :: data1(cases,2), data2(cases,3)

! both data1 and data2 are explicit-shape

! arrays and have zero size; data1 has

! shape [ 0 , 2] and data2 has the shape

! [ 0 , 3]

DO i = 1,n+1

  a(i) = SIN(x(i))

  b(i:n) = b(i:n) + a(i)

ENDDO

! the array section b(i:n) becomes a

! zero-sized array in the last iteration of

! the DO loop

WRITE(*,"(9a)",ADVANCE="NO") &

(/ (title(i),i=1,cols) /)

! if the variable cols is less than 1, then

! the array constructor contains no values

! and no data will be output