pTAL Guidelines for TAL Programmers

Coding Guidelines
pTAL Guidelines for TAL Programmers—527256-002
2-7
Referencing Variables and Parameters
Example 2-2 on page 2-6 does not work in a pTAL program running as a native
process because native compilers optimize the time required to access variables and
parameters by:
•
Arranging the items in memory for optimal access (the actual order of the variables
in memory might differ from the order in which you declare them)
•
Inserting filler between items
To ensure the position of one variable relative to another in pTAL, use elements of an
array, fields of a structure, or an equivalenced declaration.
Example 2-3 on page 2-7 has a buffer in which it scans messages. A STRING variable
with the value zero immediately follows the buffer and ensures that the scan stops.
Example 2-3 on page 2-7 might not work in pTAL because the native compiler might
not allocate space for stopper immediately after the array scan_buff. Two ways to
achieve the same effect in pTAL are:
•
Make scan_buff one byte longer and store zero in its last element, as in
Example 2-4 on page 2-7.
•
Declare scan_buff and stopper as fields of a structure, as in Example 2-5 on
page 2-8. pTAL allocates the fields of a structure in the order in which you declare
them.
Example 2-4 on page 2-7 and Example 2-5 on page 2-8 work in both TAL and pTAL.
Example 2-3. Zero in Variable After Buffer Ensures That Scan Stops (TAL Only)
STRING scan_buff [0:79]; ! Buffer for scanning stopper
STRING stopper := 0; ! immediately follows buffer
SCAN scan_buff WHILE " "; ! If line is blank,
! zero in stopper stops scan
Example 2-4. Zero in Last Element of Buffer Ensures That Scan Stops
STRING scan_buff[0:80]; ! Buffer for scanning
scan_buff[80] := 0; ! Last element of buffer is zero
SCAN scan_buff WHILE " "; ! If line is blank,
! zero in scan_buff[80] stops scan