Open Watcom FORTRAN 77 Language Reference

FORTRAN Statements
2.13 COMMON Statement
COMMON [/[cb]/] nlist [[,]/[cb]/ nlist] ...
where:
cb
nlist
is a common block name.
is a list of names each separated by a comma.
If cb is omitted, the blank common block is assumed. If specified, cb is called a named common block.
The names appearing in nlist can be variable names, array names, and array declarators. Dummy
arguments are not allowed in nlist.
The COMMON statement allows sharing of blocks of storage between subprograms. Each name appearing in
the nlist following a common block name cb is declared to belong to that common block. A variable or
an array name can belong to only one common block. A common block name can occur more than once in
the same COMMON statement as well as in more than one COMMON statement. Lists following successive
appearances of the same common block name in COMMON statements are considered a continuation of the
list of names belonging to the common block. A variable or an array can appear in a COMMON statement
only once.
Common blocks are defined as follows. A common block is one consecutive block of storage. It consists
of all the storage sequences of all the entities specified in all the lists declared to belong to that common
block. The order in which each entity appears in a common block is defined by the order in which they
appear in the lists. Storage sequences associated to a common block through the EQUIVALENCE statement
are considered to belong to that common block. In this way a common block may only be extended beyond
the last storage unit. The size of a common block is the sum of all the storage sequences of all the names
belonging to that common block plus any storage sequence which extends the common block through
equivalence association.
An EQUIVALENCE statement must not cause storage sequences of two different common blocks to
become associated nor should they extend the common block by adding storage units preceding the first
storage unit of the common block.
Example:
DIMENSION A(5)
COMMON /COMBLK/ A,B(10),C
In this example, the common block COMBLK contains the array A followed by the array B and finally the
variable C.
COMMON Statement 31