Char array dimensioning confusion in Fortran 77

Question

I have the following piece of code in my subroutine:

character    x*256 ,y*80
common /foo/ x     ,y(999)

Well, I did not actually write this. So I don't understant the dimensions here. Is y an 999 element wide array of 80 character long strings?

If so, how can I define this properly in Fortran 90, without the common block?

Answer 1

I will first say that the code you have is "proper" Fortran 90, but I agree with wanting to move away from common blocks.

There is, essentially, nothing specific to the character nature of the declaration. Whenever

<type> A
common /foo/ A(<size>)

is used there are two parts to the declaration of A, as well as the common association: the type and the dimension. Ignoring the association, declaration of the dimension in the common statement is allowed and the above is like

<type> A
dimension A(<size>)

This is in turn the same as

<type>, dimension(<size>) :: A

Coming to the specific example, the type is a character of length 80. Your non-common declaration would simply be

character(len=80), dimension(999) :: y

Indeed, then, y is a rank-1 array of size 999 of length-80 characters. y(10) is a scalar length-80 character (the 10th element of the array y).

x(10) isn't correct syntax, as the (10) is array indexing, and x is a scalar. For substrings a different indexing is required. x(10:10) is the 10th character of the character variable x; y(10)(10:10) is the 10th character of the 10th element of the character array y.