An explicit-shape array is declared with explicit values for the bounds in each dimension of the array. An explicit-shape specification takes the following form:
If the lower bound is not specified, it is assumed to be 1.
The bounds can be specified as constant or nonconstant expressions, as follows:
The bounds are not affected by any redefinition or undefinition of the variables in the specification expression that occurs while the procedure is executing.
The following explicit-shape arrays can specify nonconstant bounds:
The following are examples of explicit-shape specifications:
INTEGER I(3:8, -2:5) ! Rank-two array; range of dimension one is ... ! 3 to 8, range of dimension two is -2 to 5 SUBROUTINE SUB(A, B, C) INTEGER :: B, C REAL, DIMENSION(B:C) :: A ! Rank-one array; range is B to C
An automatic array is an explicit-shape array that is a local variable. Automatic arrays are only allowed in function and subroutine subprograms, and are declared in the specification part of the subprogram. At least one bound of an automatic array must be a nonconstant specification expression. The bounds are determined when the subprogram is called.
The following example shows automatic arrays:
SUBROUTINE SUB1 (A, B) INTEGER A, B, LOWER COMMON /BOUND/ LOWER ... INTEGER AUTO_ARRAY1(B) ... INTEGER AUTO_ARRAY2(LOWER:B) ... INTEGER AUTO_ARRAY3(20, B*A/2) END SUBROUTINE
An adjustable array is an explicit-shape array that is a dummy argument to a subprogram. At least one bound of an adjustable array must be a nonconstant specification expression. The bounds are determined when the subprogram is called.
The array specification can contain integer variables that are either dummy arguments or variables in a common block.
When the subprogram is entered, each dummy argument specified in the bounds must be associated with an actual argument. If the specification includes a variable in a common block, the variable must have a defined value. The array specification is evaluated using the values of the actual arguments, as well as any constants or common block variables that appear in the specification.
The size of the adjustable array must be less than or equal to the size of the array that is its corresponding actual argument.
To avoid possible errors in subscript evaluation, make sure that the bounds expressions used to declare multidimensional adjustable arrays match the bounds as declared by the caller.
In the following example, the function computes the sum of the elements of a rank-two array. Notice how the dummy arguments M and N control the iteration:
FUNCTION THE_SUM(A, M, N) DIMENSION A(M, N) SUMX = 0.0 DO J = 1, N DO I = 1, M SUMX = SUMX + A(I, J) END DO END DO THE_SUM = SUMX END FUNCTION
The following are examples of calls on THE_SUM:
DIMENSION A1(10,35), A2(3,56) SUM1 = THE_SUM(A1,10,35) SUM2 = THE_SUM(A2,3,56)
The following example shows how the array bounds determined when the procedure is entered do not change during execution:
DIMENSION ARRAY(9,5) L = 9 M = 5 CALL SUB(ARRAY,L,M) END SUBROUTINE SUB(X,I,J) DIMENSION X(-I/2:I/2,J) X(I/2,J) = 999 J = 1 I = 2 END
The assignments to I and J do not affect the declaration of adjustable array X as X(-4:4,5) on entry to subroutine SUB.
For More Information:
For details on specification expressions, see Section 18.104.22.168.