🚀 go-pugleaf

In article <C0pDpw.AxK@fs7.ece.cmu.edu>, winstead@faraday.ece.cmu.edu 
(Charles Holden Winstead) writes:
|>
|>This is probably an easy question, but I didn't find it in either of my
|>FORTRAN 77 texts.  I have a program which has a section labelled BLOCK DATA
|>where it defines a bunch of variables as common and fills them with data.
|>My question is when is this done, before execution?  Is there any official 
|>description of this?  Also this program contains a bunch of subroutines
|>that I'd like to place into separate files and link their object files at
|>compilation, and I was wondering how to handle common blocks and this 
|>block data section.
|>

According to the FORTRAN 77 standard (and also Fortran 90), the only place
that a variable in a COMMON block may be data-initialized is in a BLOCK DATA
subprogram.  So if you want your COMMON data to have an initial value when the
program starts, use a BLOCK DATA; a BLOCK DATA subprogram has no executable
part and is "linked" in with the rest of your program.  The initialization
typically happens at compile-time, though all that's required is that it
happen before execution starts.

Many implementations allow you to data-initialize COMMONs outside of a
BLOCK DATA.  If you use this extension, make very sure that ONE AND ONLY ONE
program unit initializes a given COMMON block, or else you're sure to see
some rather interesting and unpredictable results.
--

Steve Lionel                    lionel@quark.enet.dec.com
SDT Languages Group
Digital Equipment Corporation
110 Spit Brook Road
Nashua, NH 03062