The Natural stack is a kind of "intermediate storage" in
which you can store Natural commands, user-defined commands, and input data to
be used by an INPUT
statement.
This document covers the following topics:
In the stack you can store a series of functions which are frequently executed one after the other, such as a series of logon commands.
The data/commands stored in the stack are "stacked" on top of one another. You can decide whether to put them on top or at the bottom of the stack. The data/command in the stack can only be processed in the order in which they are stacked, beginning from the top of the stack.
In a program, you may reference the system variable
*DATA to
determine the content of the stack (see the
System
Variables documentation for further information).
The processing of the commands/data stored in the stack differs depending on the function being performed.
If a command is expected, that is, the NEXT prompt is about
to be displayed, Natural first checks if a command is on the top of the stack.
If there is, the NEXT prompt is suppressed and the command is read
and deleted from the stack; the command is then executed as if it had been
entered manually in response to the NEXT prompt.
If an INPUT
statement containing input fields is being executed, Natural first checks if
there are any input data on the top of the stack. If there are, these data are
passed to the INPUT statement (in
delimiter
mode); the data read from the stack must be format-compatible with
the variables in the INPUT statement; the data are then deleted
from the stack. See also
Processing
Data from the Natural Stack in the INPUT
statement description.
If an INPUT statement was executed using data from the
stack, and this INPUT statement is re-executed via a
REINPUT statement,
the INPUT statement screen will be re-executed displaying the same
data from the stack as when it was executed originally. With the
REINPUT statement, no further data are read from the stack.
When a Natural program terminates normally, the stack is flushed
beginning from the top until either a command is on the top of the stack or the
stack is cleared. When a Natural program is terminated via the terminal command
%% or with an error,
the stack is cleared entirely.
The following methods can be used to place data/commands on the stack:
The Natural profile parameter STACK may be used to
place data/commands on the stack. The STACK parameter
(described in the Parameter Reference) can be specified by
the Natural administrator in the Natural parameter module at the installation
of Natural; or you can specify it as a dynamic parameter when you invoke
Natural.
When data/commands are to be placed on the stack via the
STACK parameter, multiple commands must be separated
from one another by a semicolon (;). If a command is to be passed within a
sequence of data or command elements, it must be preceded by a semicolon.
Data for multiple INPUT statements must be
separated from one another by a colon (:). Data that are to be read by a
separate INPUT statement must be preceded by a colon. If a command
is to be stacked which requires parameters, no colon is to be placed between
the command and the parameters.
Semicolon and colon must not be used within the input data themselves as they will be interpreted as separation characters.
The STACK
statement can be used within a program to place data/commands in the stack. The
data elements specified in one STACK statement will be used for
one INPUT statement,
which means that if data for multiple INPUT statements are to be
placed on the stack, multiple STACK statements must be used.
Data may be placed on the stack either unformatted or formatted:
If unformatted data are read from the stack, the data string is
interpreted in delimiter mode and the characters specified with the session
parameters IA
(Input Assignment character) and ID (Input Delimiter
character) are processed as control characters for keyword assignment and data separation.
If formatted data are placed on the stack, each content of a field
will be separated and passed to one input field in the corresponding
INPUT statement. If the data to be placed on the stack contains
delimiter, control or DBCS characters, it should be placed formatted on the
stack to avoid unintentional interpretation of these characters.
See the Statements documentation for further
information on the STACK statement.
The execution of a FETCH or
RUN statement that
contains parameters to be passed to the invoked program will result in these
parameters being placed on top of the stack.
The Natural terminal command %.P deletes the topmost entry
from the Natural stack.
The contents of the stack can be deleted with the RELEASE
statement. See the Statements documentation for details on
the RELEASE
statement.
Note:
When a Natural program is terminated via the terminal command
%% or with an error,
the stack is cleared entirely.