Guardian Programmer's Guide

Introduction to Guardian Programming
Guardian Programmer’s Guide — 421922-014
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The Startup Sequence
For printers, the operating system allows the application not only to write data to the
printer file but also to provide control operations such as advancing the paper to the
top of the page or changing the character font of printers that have that capability. The
printer control language (PCL) provides application control capability. Section 11,
Communicating With Printers, provides details.
For magnetic tape, an application program can perform read and write operations as
well as control operations such as rewinding the tape. The operating system supports
both labeled and unlabeled tape. Section 12, Communicating With Magnetic Tape,
describes the programmatic interface.
Sequential Input/Output (SIO) Routines
The sequential input/output (SIO) routines provide a higher-level interface than the file
system. They are useful for reading or writing text streams to or from a terminal, a
printer, or a disk file in EDIT format. For example, you might use SIO for command
input or listing files.
A higher-level interface like the one provided by SIO is necessary for accessing files in
EDIT format, because these files have a data structure in addition to what the file
system understands.
The programmatic interface to the SIO routines is made up of a set of Guardian
procedure calls and is described in Section 15, Using the Sequential Input/Output
Procedures.
The IOEdit Routines
The IOEdit routines provide an alternative to SIO for accessing files in EDIT format.
Like SIO, IOEdit provides a higher-level interface than the file system.
Section 14, Using the IOEdit Procedures, describes the programmatic interface to
IOEdit.
The Startup Sequence
When a new process starts, a sequence of messages usually provides that process
with some information about the process’s environment: specifically, some user-
specified file names used by the process and other user-specified information in the
form of ASSIGNs or PARAMs. This startup sequence is usually observed whenever
one process creates another; the creating process sends the information to the new
process, but it is up to the new process to decide what to do with the information. The
TACL process is an example of a process that always sends this information to the
processes it creates.
Section 8, Communicating With a TACL Process, provides details of the startup
sequence between the TACL process and a process it creates. For information about
how you can construct and send the startup message sequence from your application,
see Section 16, Creating and Managing Processes.