Access elements of returned array in Fortran

Question

How does one access an element of an array that is returned from a function? For example, shape() returns an array of integers. How does one compare an element of that array to an integer? The following does not compile:

integer :: a
integer, dimension(5) :: b

a = 5
if (a .eq. shape(b)) then
    print *, 'equal'
end if

The error is:

if (a .eq. shape(c)) then
    1
Error: IF clause at (1) requires a scalar LOGICAL expression

I understand that this is because shape(c) returns an array. However, accessing an element of the array does not appear to be possible like so: shape(c)(1)

Now if I add these two lines:

integer, dimension(1) :: c
c = shape(b)

...and change the if clause to this:

if (a .eq. c(1)) then

... then it works. But do I really have to declare an extra array variable to hold the return value of shape(), or is there some other way to do it?

Answer 1

Further to the answers that deal with SHAPE and logical expressions etc, the general answer to your question "How does one access an element of an array that is returned from a function?" is

• you assign the expression that has the function reference to an array variable, and then index that array variable.

• you use the expression that has the function reference as an actual argument to a procedure that takes a dummy array argument, and does the indexing for you.

Consequently, the general answer to your last questions "But do I really have to declare an extra array variable to hold the return value of shape(), or is there some other way to do it?" is "Yes, you do need to declare another array variable" and hence "No, there is no other way".

(Note that reasonable optimising compilers will avoid the need for any additional memory operations/allocations etc once they have the result of the array function, it's really just a syntax issue.)

The rationale for this particular aspect of language design is sometimes ascribed to a need to avoid syntax ambiguity and confusion for array function results that are of character type (they could potentially be indexed and/or substringed - how do you tell what was intended?). Others think it was done this way just to annoy C programmers.