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.