This document covers the following topics:
Generally, the following rules apply:
A dynamic alphanumeric field may be used wherever an alphanumeric field is allowed.
A dynamic binary field may be used wherever a binary field is allowed.
A dynamic Unicode field may be used wherever a Unicode field is allowed.
Dynamic variables are not allowed within the
SORT statement. To use
dynamic variables in a DISPLAY,
WRITE,
PRINT,
REINPUT or
INPUT statement, you
must use either the session parameter AL or
EM to
define the length of the variable.
The used length (as indicated by the Natural system variable
*LENGTH,
see Value Space
Currently Used for a Dynamic Variable) and the size of the
allocated storage of dynamic variables are equal to zero until the variable is
accessed as a target operand for the first time. Due to assignments or other
manipulation operations, dynamic variables may be firstly allocated or extended
(reallocated) to the exact size of the source operand.
The size of a dynamic variable may be extended if it is used as a modifiable operand (target operand) in the following statements:
ASSIGN
|
operand1 (destination
operand in an assignment).
|
CALLNAT
|
See Parameter Transfer with Dynamic
Variables (except if AD=O, or if BY
VALUE exists in the corresponding parameter data area).
|
COMPRESS
|
operand2, see
Processing.
|
EXAMINE
|
operand1 in the
DELETE
REPLACE clause.
|
MOVE
|
operand2 (destination
operand), see Function.
|
PERFORM
|
(except if AD=O, or if BY VALUE exists
in the corresponding parameter data area).
|
READ WORK
FILE
|
operand1 and
operand2, see
Handling
of Large and Dynamic Variables.
|
SEPARATE
|
operand4.
|
SELECT (SQL)
|
Parameter in the
INTO clause.
|
SEND
METHOD
|
operand3 (except if
AD=O).
|
Currently, there is the following limit concerning the usage of large variables:
CALL
|
Parameter size less than 64 KB per parameter (no limit for
CALL with INTERFACE4 option).
|
In the following sections, the use of dynamic variables is discussed in more detail on the basis of examples.
Generally, an assignment is done in the current used length (as
indicated by the Natural system variable
*LENGTH)
of the source operand. If the destination operand is a dynamic variable, its
current allocated size is possibly extended in order to move the source operand
without truncation.
Example:
#MYDYNTEXT1 := OPERAND MOVE OPERAND TO #MYDYNTEXT1 /* #MYDYNTEXT1 IS AUTOMATICALLY EXTENDED UNTIL THE SOURCE OPERAND CAN BE COPIED
MOVE ALL,
MOVE ALL
UNTIL with dynamic target operands are defined as
follows:
MOVE ALL moves the source operand repeatedly to the
target operand until the used length (*LENGTH) of
the target operand is reached. The system variable
*LENGTH is not modified. If
*LENGTH is zero, the statement will be
ignored.
MOVE ALL operand1 TO
operand2 UNTIL operand3 moves
operand1 repeatedly to
operand2 until the length specified in
operand3 is reached. If
operand3 is greater than
*LENGTH(operand2),
operand2 is extended and
*LENGTH(operand2) is
set to operand3. If
operand3 is less than
*LENGTH(operand2), the
used length is reduced to operand3. If
operand3 equals
*LENGTH(operand2), the
behavior is equivalent to MOVE ALL.
Example:
#MYDYNTEXT1 := 'ABCDEFGHIJKLMNO' /* *LENGTH(#MYDYNTEXT1) = 15
MOVE ALL 'AB' TO #MYDYNTEXT1 /* CONTENT OF #MYDYNTEXT1 = 'ABABABABABABABA';
/* *LENGTH IS STILL 15
MOVE ALL 'CD' TO #MYDYNTEXT1 UNTIL 6 /* CONTENT OF #MYDYNTEXT1 = 'CDCDCD';
/* *LENGTH = 6
MOVE ALL 'EF' TO #MYDYNTEXT1 UNTIL 10 /* CONTENT OF #MYDYNTEXT1 = 'EFEFEFEFEF';
/* *LENGTH = 10
MOVE JUSTIFIED is rejected at compile time if the target
operand is a dynamic variable.
MOVE SUBSTR and MOVE TO SUBSTR are allowed.
MOVE SUBSTR will lead to a runtime error if a sub-string behind
the used length of a dynamic variable (*LENGTH) is
referenced. MOVE TO SUBSTR will lead to a runtime error if a
sub-string position behind *LENGTH + 1 is
referenced, because this would lead to an undefined gap in the content of the
dynamic variable. If the target operand should be extended by MOVE TO
SUBSTR (for example if the second operand is set to
*LENGTH+1), the third operand is mandatory.
Valid syntax:
#OP2 := *LENGTH(#MYDYNTEXT1) MOVE SUBSTR (#MYDYNTEXT1, #OP2) TO OPERAND /* MOVE LAST CHARACTER TO OPERAND #OP2 := *LENGTH(#MYDYNTEXT1) + 1 MOVE OPERAND TO SUBSTR(#MYDYNTEXT1, #OP2, #lEN_OPERAND) /* CONCATENATE OPERAND TO #MYDYNTEXT1
Invalid syntax:
#OP2 := *LENGTH(#MYDYNTEXT1) + 1 MOVE SUBSTR (#MYDYNTEXT1, #OP2, 10) TO OPERAND /* LEADS TO RUNTIME ERROR; UNDEFINED SUB-STRING #OP2 := *LENGTH(#MYDYNTEXT1 + 10) MOVE OPERAND TO SUBSTR(#MYDYNTEXT1, #OP2, #EN_OPERAND) /* LEADS TO RUNTIME ERROR; UNDEFINED GAP #OP2 := *LENGTH(#MYDYNTEXT1) + 1 MOVE OPERAND TO SUBSTR(#MYDYNTEXT1, #OP2) /* LEADS TO RUNTIME ERROR; UNDEFINED LENGTH
Example:
#MYDYNTEXT1 := #MYSTATICVAR1 #MYSTATICVAR1 := #MYDYNTEXT2
If the source operand is a static variable, the used length of the
dynamic destination operand (*LENGTH(#MYDYNTEXT1))
is set to the format length of the static variable and the source value is
copied in this length including trailing blanks (alphanumeric and Unicode
fields) or binary zeros (for binary fields).
If the destination operand is static and the source operand is dynamic, the dynamic variable is copied in its currently used length. If this length is less than the format length of the static variable, the remainder is filled with blanks (for alphanumeric and Unicode fields) or binary zeros (for binary fields). Otherwise, the value will be truncated. If the currently used length of the dynamic variable is 0, the static target operand is filled with blanks (for alphanumeric and Unicode fields) or binary zeros (for binary fields).
Dynamic variables can be initialized with blanks (alphanumeric and
Unicode fields) or zeros (binary fields) up to the currently used length (=
*LENGTH)
using the RESET
statement. The system variable *LENGTH is not
modified.
Example:
DEFINE DATA LOCAL 1 #MYDYNTEXT1 (A) DYNAMIC END-DEFINE #MYDYNTEXT1 := 'SHORT TEXT' WRITE *LENGTH(#MYDYNTEXT1) /* USED LENGTH = 10 RESET #MYDYNTEXT1 /* USED LENGTH = 10, VALUE = 10 BLANKS
To initialize a dynamic variable with a specified value in a specified
size, the MOVE ALL UNTIL statement may be used.
Example:
MOVE ALL 'Y' TO #MYDYNTEXT1 UNTIL 15 /* #MYDYNTEXT1 CONTAINS 15 'Y'S, USED LENGTH = 15
If a modifiable operand is a dynamic variable, its current allocated
size is possibly extended in order to perform the operation without truncation
or an error message. This is valid for the concatenation (COMPRESS) and separation of
dynamic alphanumeric variables (SEPARATE).
Example:
** Example 'DYNAMX01': Dynamic variables (with COMPRESS and SEPARATE) ************************************************************************ DEFINE DATA LOCAL 1 #MYDYNTEXT1 (A) DYNAMIC 1 #TEXT (A20) 1 #DYN1 (A) DYNAMIC 1 #DYN2 (A) DYNAMIC 1 #DYN3 (A) DYNAMIC END-DEFINE * MOVE ' HELLO WORLD ' TO #MYDYNTEXT1 WRITE #MYDYNTEXT1 (AL=25) 'with length' *LENGTH (#MYDYNTEXT1) /* dynamic variable with leading and trailing blanks * MOVE ' HELLO WORLD ' TO #TEXT * MOVE #TEXT TO #MYDYNTEXT1 WRITE #MYDYNTEXT1 (AL=25) 'with length' *LENGTH (#MYDYNTEXT1) /* dynamic variable with whole variable length of #TEXT * COMPRESS #TEXT INTO #MYDYNTEXT1 WRITE #MYDYNTEXT1 (AL=25) 'with length' *LENGTH (#MYDYNTEXT1) /* dynamic variable with leading blanks of #TEXT * * #MYDYNTEXT1 := 'HERE COMES THE SUN' SEPARATE #MYDYNTEXT1 INTO #DYN1 #DYN2 #DYN3 IGNORE * WRITE / #MYDYNTEXT1 (AL=25) 'with length' *LENGTH (#MYDYNTEXT1) WRITE #DYN1 (AL=25) 'with length' *LENGTH (#DYN1) WRITE #DYN2 (AL=25) 'with length' *LENGTH (#DYN2) WRITE #DYN3 (AL=25) 'with length' *LENGTH (#DYN3) /* #DYN1, #DYN2, #DYN3 are automatically extended or reduced * EXAMINE #MYDYNTEXT1 FOR 'SUN' REPLACE 'MOON' WRITE / #MYDYNTEXT1 (AL=25) 'with length' *LENGTH (#MYDYNTEXT1) /* #MYDYNTEXT1 is automatically extended or reduced * END
Note:
In case of non-dynamic variables, an error message may be
returned.
Generally, a read-only operation (such as a comparison) with a dynamic variable is done with its currently used length. Dynamic variables are processed like static variables if they are used in a read-only (non-modifiable) context.
Example:
IF #MYDYNTEXT1 = #MYDYNTEXT2 OR #MYDYNTEXT1 = "**" THEN ... IF #MYDYNTEXT1 < #MYDYNTEXT2 OR #MYDYNTEXT1 < "**" THEN ... IF #MYDYNTEXT1 > #MYDYNTEXT2 OR #MYDYNTEXT1 > "**" THEN ...
Trailing blanks for alphanumeric and Unicode variables or leading binary
zeros for binary variables are processed in the same way for static and dynamic
variables. For example, alphanumeric variables containing the values
AA and AA followed by a blank will be considered
being equal, and binary variables containing the values H’0000031’
and H’3031’ will be considered being equal. If a comparison result
should only be TRUE in case of an exact copy, the used lengths of
the dynamic variables have to be compared in addition. If one variable is an
exact copy of the other, their used lengths are also equal.
Example:
#MYDYNTEXT1 := 'HELLO' /* USED LENGTH IS 5
#MYDYNTEXT2 := 'HELLO ' /* USED LENGTH IS 10
IF #MYDYNTEXT1 = #MYDYNTEXT2 THEN ... /* TRUE
IF #MYDYNTEXT1 = #MYDYNTEXT2 AND
*LENGTH(#MYDYNTEXT1) = *LENGTH(#MYDYNTEXT2) THEN ... /* FALSE
Two dynamic variables are compared position by position (from left to right for alphanumeric variables, and right to left for binary variables) up to the minimum of their used lengths. The first position where the variables are not equal determines if the first or the second variable is greater than, less than or equal to the other. The variables are equal if they are equal up to the minimum of their used lengths and the remainder of the longer variable contains only blanks for alphanumeric dynamic variables or binary zeros for binary dynamic variables. To compare two Unicode dynamic variables, trailing blanks are removed from both values before the ICU collation algorithm is used to compare the two resulting values. See also Logical Condition Criteria in the Unicode and Code Page Support documentation.
Example:
#MYDYNTEXT1 := 'HELLO1' /* USED LENGTH IS 6 #MYDYNTEXT2 := 'HELLO2' /* USED LENGTH IS 10 IF #MYDYNTEXT1 < #MYDYNTEXT2 THEN ... /* TRUE #MYDYNTEXT2 := 'HALLO' IF #MYDYNTEXT1 > #MYDYNTEXT2 THEN ... /* TRUE
Comparisons between dynamic and static variables are equivalent to comparisons between dynamic variables. The format length of the static variable is interpreted as its used length.
Example:
#MYSTATTEXT1 := 'HELLO' /* FORMAT LENGTH OF MYSTATTEXT1 IS A20 #MYDYNTEXT1 := 'HELLO' /* USED LENGTH IS 5 IF #MYSTATTEXT1 = #MYDYNTEXT1 THEN ... /* TRUE IF #MYSTATTEXT1 > #MYDYNTEXT1 THEN ... /* FALSE
The comparison of the break control field with its old value is performed position by position from left to right. If the old and the new value of the dynamic variable are of different length, then for comparison, the value with shorter length is padded to the right (with blanks for alphanumeric and Unicode dynamic values or binary zeros for binary values).
In case of an alphanumeric or Unicode break control field, trailing blanks are not significant for the comparison, that is, trailing blanks do not mean a change of the value and no break occurs.
In case of a binary break control field, trailing binary zeros are not significant for the comparison, that is, trailing binary zeros do not mean a change of the value and no break occurs.
Dynamic variables may be passed as parameters to a called program object
(CALLNAT,
PERFORM). A
call-by-reference is possible because the value space of a dynamic variable is
contiguous. A call-by-value causes an assignment with the variable definition
of the caller as the source operand and the parameter definition as the
destination operand. A call-by-value result causes in addition the movement in
the opposite direction.
For a call-by-reference, both definitions must be DYNAMIC.
If only one of them is DYNAMIC, a runtime error is raised. In the
case of a call-by-value (result), all combinations are possible. The following
table illustrates the valid combinations:
| Caller | Parameter | |
|---|---|---|
| Static | Dynamic | |
| Static | Yes | No |
| Dynamic | No | Yes |
The formats of dynamic variables A or B must match.
| Caller | Parameter | |
|---|---|---|
| Static | Dynamic | |
| Static | Yes | Yes |
| Dynamic | Yes | Yes |
Note:
In the case of static/dynamic or dynamic/static definitions, a value
truncation may occur according to the data transfer rules of the appropriate
assignments.
** Example 'DYNAMX02': Dynamic variables (as parameters) ************************************************************************ DEFINE DATA LOCAL 1 #MYTEXT (A) DYNAMIC END-DEFINE * #MYTEXT := '123456' /* extended to 6 bytes, *LENGTH(#MYTEXT) = 6 * CALLNAT 'DYNAMX03' USING #MYTEXT * WRITE *LENGTH(#MYTEXT) /* *LENGTH(#MYTEXT) = 8 * END
Subprogram DYNAMX03:
** Example 'DYNAMX03': Dynamic variables (as parameters) ************************************************************************ DEFINE DATA PARAMETER 1 #MYPARM (A) DYNAMIC BY VALUE RESULT END-DEFINE * WRITE *LENGTH(#MYPARM) /* *LENGTH(#MYPARM) = 6 #MYPARM := '1234567' /* *LENGTH(#MYPARM) = 7 #MYPARM := '12345678' /* *LENGTH(#MYPARM) = 8 EXPAND DYNAMIC VARIABLE #MYPARM TO 10 /* 10 bytes are allocated * WRITE *LENGTH(#MYPARM) /* *LENGTH(#MYPARM) = 8 * /* content of #MYPARM is moved back to #MYTEXT /* used length of #MYTEXT = 8 * END
** Example 'DYNAMX04': Dynamic variables (as parameters)
************************************************************************
DEFINE DATA LOCAL
1 #MYTEXT (A) DYNAMIC
END-DEFINE
*
#MYTEXT := '123456' /* extended to 6 bytes, *LENGTH(#MYTEXT) = 6
*
CALLNAT 'DYNAMX05' USING #MYTEXT
*
WRITE *LENGTH(#MYTEXT) /* *LENGTH(#MYTEXT) = 8
/* at least 10 bytes are
/* allocated (extended in DYNAMX05)
*
END
Subprogram DYNAMX05:
** Example 'DYNAMX05': Dynamic variables (as parameters) ************************************************************************ DEFINE DATA PARAMETER 1 #MYPARM (A) DYNAMIC END-DEFINE * WRITE *LENGTH(#MYPARM) /* *LENGTH(#MYPARM) = 6 #MYPARM := '1234567' /* *LENGTH(#MYPARM) = 7 #MYPARM := '12345678' /* *LENGTH(#MYPARM) = 8 EXPAND DYNAMIC VARIABLE #MYPARM TO 10 /* 10 bytes are allocated * WRITE *LENGTH(#MYPARM) /* *LENGTH(#MYPARM) = 8 * END
Dynamic and large variables can sensibly be used with the
CALL statement when the
option INTERFACE4 is used.
Using this option leads to an interface to the 3GL program with a different
parameter structure.
This usage requires some minor changes in the 3GL program, but
provides the following significant benefits as compared with the older
FINFO structure.
No limitation on the number of passed parameters (former limit 40).
No limitation on the parameter's data size (former limit 64 KB per parameter).
Full parameter information can be passed to the 3GL program including array information. Exported functions are provided which allow secure access to the parameter data (formerly you had to take care not to overwrite memory inside of Natural)
For further information on the FINFO structure, see the
CALL
INTERFACE4 statement.
Before calling a 3GL program with dynamic parameters, it is important
to ensure that the necessary buffer size is allocated. This can be done
explicitly with the EXPAND statement.
If an initialized buffer is required, the dynamic variable can be set
to the initial value and to the necessary size by using the MOVE ALL
UNTIL statement. Natural provides a set of functions that allow the 3GL
program to obtain information about the dynamic parameter and to modify the
length when parameter data is passed back.
Example:
MOVE ALL ' ' TO #MYDYNTEXT1 UNTIL 10000 /* a buffer of length 10000 is allocated /* #MYDYNTEXT1 is initialized with blanks /* and *LENGTH(#MYDYNTEXT1) = 10000 CALL INTERFACE4 'MYPROG' USING #MYDYNTEXT1 WRITE *LENGTH(#MYDYNTEXT1) /* *LENGTH(#MYDYNTEXT1) may have changed in the 3GL program
For a more detailed description, refer to the
CALL statement in the
Statements documentation.
The following topics are covered below:
Large and dynamic variables can be written into work files or read from
work files using the two work file types PORTABLE and
UNFORMATTED. For these types, there is no size restriction for
dynamic variables. However, large variables may not exceed a maximum
field/record length of 32766 bytes.
For the work file type PORTABLE, the field information is
stored within the work file. The dynamic variables are resized during
READ if the field size in the record is different from the current
size.
The work file type UNFORMATTED can be used, for example,
to read a video from a database and store it in a file directly playable by
other utilities. In the WRITE WORK statement, the fields are
written to the file with their byte length. All data types
(DYNAMIC or not) are treated the same. No structural information
is inserted. Note that Natural uses a buffering mechanism, so you can expect
the data to be completely written only after a CLOSE WORK. This is
especially important if the file is to be processed with another utility while
Natural is running.
With the READ WORK statement, fields of fixed length are
read with their whole length. If the end-of-file is reached, the remainder of
the current field is filled with blanks. The following fields are unchanged. In
the case of DYNAMIC data types, all the remainder of the file is
read unless it exceeds 1073741824 bytes. If the end of file is reached, the
remaining fields (variables) are kept unchanged (normal Natural behavior).
The work file types ASCII, ASCII-COMPRESSED and SAG (binary) cannot handle dynamic variables and will produce an error. Large variables for these work file types pose no problem unless the maximum field/record length of 32766 bytes is exceeded.
In conjunction with the READ
WORK FILE statement, the work file type TRANSFER
can handle dynamic variables. There is no size limit for dynamic variables. The
work file type ENTIRE CONNECTION cannot handle dynamic variables.
They can both, however, handle large variables with a maximum field/record
length of 1073741824 bytes.
In conjunction with the WRITE
WORK FILE statement, the work file type TRANSFER
can handle dynamic variables with a maximum field/record length of 32766 bytes.
The work file type ENTIRE CONNECTION cannot handle dynamic
variables. They can both, however, handle large variables with a maximum
field/record length of 1073741824 bytes.
Depending on the data types, the related database format A or format B
is generated. For the databases' data type VARCHAR the Natural
length of the column is set to the maximum length of the data type as defined
in the DBMS. If a data type is very large, the keyword DYNAMIC is
generated at the length field position.
For all varying length columns, an LINDICATOR field
L@<column-name> will be
generated. For the databases' data type VARCHAR, an
LINDICATOR field with format/length I2 will be generated. For
large data types (see list below) the format/length will be I4.
In the context of database access, the LINDICATOR handling
offers the chance to get the length of the field to be read or to set the
length of the field to be written independent of a defined buffer length (or
independent of *LENGTH).
Usually, after a retrieval function, *LENGTH will
be set to the corresponding length indicator value.
T L Name F Leng S D Remark
:
1 L@PICTURE1 I 4 /* length indicator
1 PICTURE1 B DYNAMIC IMAGE
1 N@PICTURE1 I 2 /* NULL indicator
1 L@TEXT1 I 4 /* length indicator
1 TEXT1 A DYNAMIC TEXT
1 N@TEXT1 I 2 /* NULL indicator
1 L@DESCRIPTION I 2 /* length indicator
1 DESCRIPTION A 1000 VARCHAR(1000)
:
:
~~~~~~~~~~~~~~~~~~~~~~Extended Attributes~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~/* concerning PICTURE1
Header : ---
Edit Mask : ---
Remarks : IMAGE
The generated formats are varying length formats. The Natural programmer
has the chance to change the definition from DYNAMIC to a fixed
length definition (extended field editing) and can change, for example, the
corresponding DDM field definition for VARCHAR data types to a
multiple value field (old generation).
T L Name F Leng S D Remark
:
1 L@PICTURE1 I 4 /* length indicator
1 PICTURE1 B 1000000000 IMAGE
1 N@PICTURE1 I 2 /* NULL indicator
1 L@TEXT1 I 4 /* length indicator
1 TEXT1 A 5000 TEXT
1 N@TEXT1 I 2 /* NULL indicator
1 L@DESCRIPTION I 2 /* length indicator
M 1 DESCRIPTION A 100 VARCHAR(1000)
:
:
~~~~~~~~~~~~~~~~~~~~Extended Attributes~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~/* concerning PICTURE1
Header : ---
Edit Mask : ---
Remarks : IMAGE
To access a database with large objects (CLOBs or BLOBs), a DDM with corresponding large alphanumeric, Unicode or binary fields is required. If a fixed length is defined and if the database large object does not fit into this field, the large object is truncated. If the programmer does not know the definitive length of the database object, it will make sense to work with dynamic fields. As many reallocations as necessary are done to hold the object. No truncation is performed.
DEFINE DATA LOCAL
1 person VIEW OF xyz-person
2 last_name
2 first_name_1
2 L@PICTURE1 /* I4 length indicator for PICTURE1
2 PICTURE1 /* defined as dynamic in the DDM
2 TEXT1 /* defined as non-dynamic in the DDM
END-DEFINE
SELECT * INTO VIEW person FROM xyz-person /* PICTURE1 will be read completely
WHERE last_name = 'SMITH' /* TEXT1 will be truncated to fixed length 5000
WRITE 'length of PICTURE1: ' L@PICTURE1 /* the L-INDICATOR will contain the length
/* of PICTURE1 (= *LENGTH(PICTURE1)
/* do something with PICTURE1 and TEXT1
L@PICTURE1 := 100000
INSERT INTO xyz-person (*) VALUES (VIEW person) /* only the first 100000 Bytes of PICTURE1
/* are inserted
END-SELECT
If a format-length definition is omitted in the view, this is taken from
the DDM. In reporting mode, it is now possible to specify any length, if the
corresponding DDM field is defined as DYNAMIC. The dynamic field
will be mapped to a field with a fixed buffer length. The other way round is
not possible.
| DDM format/length definition | VIEW format / length definition | |
|---|---|---|
| (An) | - | valid |
| (An) | valid | |
| (Am) | only valid in reporting mode | |
| (A) DYNAMIC | invalid | |
| (A) DYNAMIC | - | valid |
| (A) DYNAMIC | valid | |
| (An) | only valid in reporting mode | |
| (Am / i : j) | only valid in reporting mode |
(equivalent for Format B variables)
If the LINDICATOR field is defined as an I2 field, the SQL
data type VARCHAR is used for sending or receiving the
corresponding column. If the LINDICATOR host variable is specified
as I4, a large object data type (CLOB/BLOB) is used.
If the field is defined as DYNAMIC, the column is read in
an internal loop up to its real length. The LINDICATOR field and
the system variable *LENGTH
are set to this length. In the case of a fixed-length field, the column is read
up to the defined length. In both cases, the field is written up to the value
defined in the LINDICATOR field.
If a dynamic variable is to be expanded in small quantities multiple
times (for example, byte-wise), use the EXPAND statement before the
iterations if the upper limit of required storage is (approximately) known.
This avoids additional overhead to adjust the storage needed.
Use the REDUCE
or RESIZE statement if
the dynamic variable will no longer be needed, especially for variables with a
high value of the system variable *LENGTH.
This enables Natural you to release or reuse the storage. Thus, the overall
performance may be improved.
The amount of the allocated memory of a dynamic variable may be reduced
using the REDUCE DYNAMIC
VARIABLE statement. In order to (re)allocate a variable to a
specified length, the EXPAND statement can be used.
(If the variable should be initialized, use the MOVE ALL UNTIL statement.)
** Example 'DYNAMX06': Dynamic variables (allocated memory)
************************************************************************
DEFINE DATA LOCAL
1 #MYDYNTEXT1 (A) DYNAMIC
1 #LEN (I4)
END-DEFINE
*
#MYDYNTEXT1 := 'a' /* used length is 1, value is 'a'
/* allocated size is still 1
WRITE *LENGTH(#MYDYNTEXT1)
*
EXPAND DYNAMIC VARIABLE #MYDYNTEXT1 TO 100
/* used length is still 1, value is 'a'
/* allocated size is 100
*
CALLNAT 'DYNAMX05' USING #MYDYNTEXT1
WRITE *LENGTH(#MYDYNTEXT1)
/* used length and allocated size
/* may have changed in the subprogram
*
#LEN := *LENGTH(#MYDYNTEXT1)
REDUCE DYNAMIC VARIABLE #MYDYNTEXT1 TO #LEN
/* if allocated size is greater than used length,
/* the unused memory is released
*
REDUCE DYNAMIC VARIABLE #MYDYNTEXT1 TO 0
WRITE *LENGTH(#MYDYNTEXT1)
/* free allocated memory for dynamic variable
END
Use dynamic operands where it makes sense.
Use the EXPAND statement if upper limit of memory usage
is known.
Use the REDUCE statement if the dynamic operand will no
longer be needed.
Dynamic variables may be used inside output statements such as the following:
| Statement | Notes |
|---|---|
DISPLAY
|
With these statements, you must set the format of
the output or input of dynamic variables using the
AL
(Alphanumeric Length for Output) or EM (Edit Mask)
session parameters.
|
WRITE
|
|
INPUT
|
|
REINPUT
|
-- |
PRINT
|
Because the output of the PRINT statement is
unformatted, the output of dynamic variables in the PRINT
statement need not be set using AL and
EM
parameters. In other words, these parameters may be omitted.
|
A dynamic X-array may be allocated by first specifying the number of occurrences and then expanding the length of the previously allocated array occurrences.
Example:
DEFINE DATA LOCAL 1 #X-ARRAY(A/1:*) DYNAMIC END-DEFINE * EXPAND ARRAY #X-ARRAY TO (1:10) /* Current boundaries (1:10) #X-ARRAY(*) := 'ABC' EXPAND ARRAY #X-ARRAY TO (1:20) /* Current boundaries (1:20) #X-ARRAY(11:20) := 'DEF'