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With this declaration, it is possible to specify values for Resultant_String
and Prompt_String and truncate the call list at that point. In this case, two
parameters would be passed in the CALL instruction.
You may want to use a combination of the %IMMED 0 and TRUNCATE
methods. This combination would allow you to skip the specification of
intermediate optional parameters, as well as allow you to truncate the call list
once all desired parameters have been specified.
Note that OpenVMS system services require a value to be passed by
parameters, including optional parameters; therefore, you should not use
the TRUNCATE attribute when defining optional parameters to a system
service. Instead, you should specify default values on the formal parameter
declaration.
The TRUNCATE attribute is useful when calling routines for which the
optional parameter is truly optional, for example, when calling run-time library
routines.
For More Information:
•
On the TRUNCATE attribute (HP Pascal for OpenVMS Language Reference
Manual)
6.2.6 Arbitrary Length Parameter Lists
Some run-time library routines require a variable number of parameters. For
example, there is no fixed limit on the number of values that can be passed
to functions that return the minimum or maximum value from a list of input
parameters. The LIST attribute supplied by HP Pascal allows you to indicate
the mechanism by which excess actual parameters are to be passed. For
example:
[ASYNCHRONOUS] FUNCTION MTH$DMIN1 (
D_FLOATING : DOUBLE;
EXTRA_PARAMS : [LIST] DOUBLE) : DOUBLE; EXTERNAL;
Because the function MTH$DMIN1 returns the D_floating minimum of an
arbitrary number of D_floating parameters, the formal parameter EXTRA_
PARAMS is declared with the LIST attribute. All actual parameters must be
double-precision real numbers passed by reference with value semantics.
For More Information:
On the LIST attribute (HP Pascal for OpenVMS Language Reference Manual)
6–12 Programming on OpenVMS Systems