HP 3000 Manuals

Getting Started as an MPE/iX Programmer Programmer's Guide

Hierarchy of File Overrides 

The :FILE command cannot override at run time any specifications in the
disc file label for an existing disc file.  (The file label specifies
physical characteristics of the file; record structure, file structure,
file code, and actual file name.)  Anything in the disc file label has
precedence.  Similarly, device characteristics always prevail over a
:FILE command invoked for a device file.  :FILE can override the
following:

   *   Specifications that are not in a file label for a disc file.

   *   Specifications that are not already given for a device file.

   *   Specifications given when an intrinsic in the program opens the
       file.

If the program creates a disc file at run time, then :FILE can override
the opening characteristics that the program was compiled to use and
create a file with different characteristics.

It is possible to use an intrinsic such as HPFOPEN or FOPEN to override
file equations.  When an intrinsic is set up to do this, the file
equation produced by invoking :FILE can be ignored unless the file name
given in the intrinsic opening the file is dereferenced (preceded by an
asterisk (*)).  For detailed information on the hierarchy of overrides,
and for information on how this applies to labeled tapes, refer to
Accessing Files Programmer's Guide (32650-90017).

When a :FILE command is entered that contradicts some of the HPFOPEN or
FOPEN parameters for a file, The File System maintains a hierarchy of
overrides, as shown in Figure 6-11 .


          Figure 6-11.  File System Hierarchy of Overrides 

MPE/iX 5.0 Documentation