Pointers and Mapping

Mapping is a facility provided by VMS which gets around the problem of fitting variable length data into static arrays of fixed length as imposed by FORTRAN. Essentially the area of disk in which the data reside are added to virtual memory, the mapping routines returning the start address in an integer variable. Since FORTRAN has no facilities for dealing with such pointers their use can be hazardous! Mapping and pointers should only be used according to the following rules:

• Mapping should only be done using HDS/ADAM subroutine calls - there should be no explicit reference to VMS mapping service routines.

• The value of a pointer may not be changed.

• The array pointed to may only be manipulated by a lower level subroutine. The pointer should be passed by reference using together with the dimensions of the array. Within the subroutine the array should be dynamically dimensioned unless its length is potentially zero, in which case the (*) format may be used.