EQUIVALENCE and COMMON Interaction

A common block can extend beyond its original boundaries if variables or arrays are associated with entities stored in the common block. However, a common block can only extend beyond its last element; the extended portion cannot precede the first element in the block.

Examples

The following two figures demonstrate valid and invalid extensions of the common block, respectively.

A Valid Extension of a Common Block

An Invalid Extension of a Common Block

The second example is invalid because the extended portion, B(1), precedes the first element of the common block.

The following example shows a valid EQUIVALENCE statement and an invalid EQUIVALENCE statement in the context of a common block.

  COMMON A, B, C
  DIMENSION D(3)
  EQUIVALENCE(B, D(1))      ! Valid, because common block is extended
                            !   from the end.

  COMMON A, B, C
  DIMENSION D(3)
  EQUIVALENCE(B, D(3))      ! Invalid, because D(1) would extend common
                            !   block to precede A's location.