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, see
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.
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.
There is no difference in the treatment of fixed length variables with a length of less than or equal to 253 and large variables with a length of greater than 253.
Dynamic variables are written in the length that is in effect (that is,
the value of the system variable *LENGTH
for this variable) when the WRITE WORK
FILE statement is executed. Since the length can be different
for each execution of the same WRITE WORK FILE statement, the
keyword VARIABLE must be specified.
When reading work files of type FORMATTED, a dynamic
variable is filled in the length that is in effect (that is, the value of the
system variable *LENGTH for this variable) when
the READ WORK FILE statement is executed. If the dynamic variable
is longer than the remaining data in the current record, it is padded with
blanks for alphanumeric and Unicode fields and binary zeros for binary
fields.
When reading a work file of type UNFORMATTED, a dynamic
variable is filled with the remainder of the work file. Its size is adjusted
accordingly, and is reflected in the value of the system variable
*LENGTH for this variable.
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 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'