4.18 VOLATILE Statement

The VOLATILE statement specifies that a value is entirely unpredictable, based on information local to the current program unit. It prevents specified variables, arrays, and common blocks from being optimized during compilation.

The VOLATILE statement takes the following form:

VOLATILE nlist

nlist

Is a list of variables, arrays, array declarators, named common blocks (preceded and followed by a slash), records, record arrays, or record array declarators, separated by commas.

If array names or common block names are used, the entire array or common block becomes volatile, as the following example shows.

Example

In the following statements, the named common block, BLK1, and the variables D and E are volatile. Variables P1 and P4 become volatile because of the direct equivalence of P1 and the indirect equivalence of P4.

PROGRAM TEST
LOGICAL*1 IPI(4)
INTEGER*4 A,B,C,D,E,ILOOK
INTEGER*4 P1,P2,P3,P4
COMMON /BLK1/A,B,C

VOLATILE /BLK1/,D,E
EQUIVALENCE(ILOOK,IPI)
EQUIVALENCE (A,P1)
EQUIVALENCE (P1,P4)