VOLATILE

 Prevents specified variables, arrays, and common blocks from being
 optimized during compilation.

 The VOLATILE attribute can be specified in a type declaration
 statement or VOLATILE statement, and takes one of the following
 forms:

 Type Declaration Statement:

  type, [att-ls,] VOLATILE [,attr-ls] :: obj [,obj]...

 Statement:

  VOLATILE obj [,obj]...

    type      Is a data type specifier.

    attr-ls   Is an optional list of attribute specifiers.

    obj       Is the name of an object or a common block 
              enclosed in slashes.

 A variable or COMMON block must be declared VOLATILE if it can be
 read or written in a way that is not visible to the compiler.  For
 example:

  o  If an operating system feature is used to place a variable in
     shared memory (so that it can be accessed by other programs),
     the variable must be declared VOLATILE.

  o  If a variable is modified by a routine called by the operating
     system when an asynchronous event occurs, the variable must be
     declared VOLATILE.


 If an array is declared VOLATILE, each element in the array becomes
 volatile.  If a common block is declared VOLATILE, each variable in
 the common block becomes volatile.

 If an object of derived type is declared VOLATILE, its components
 become volatile.

 If a pointer is declared VOLATILE, the pointer itself becomes
 volatile.

 A VOLATILE statement cannot specify the following:

  o  A procedure

  o  A function result

  o  A namelist group


 The VOLATILE attribute is compatible with the ALLOCATABLE,
 AUTOMATIC, DIMENSION, INTENT, OPTIONAL, POINTER, PRIVATE, PUBLIC,
 SAVE, STATIC, and TARGET attributes.