|
|
DYNAMIC Variables - *LENGTH, REDUCE, EXPAND, RESIZE
|
|
|
|
|
|
|
|
This posting is a continuation of the previous post. The intent is to provide an understanding
of the basics of DYNAMIC Variables in the hope that programmers will be more "comfortable"
with their use, and begin to utilize them more than appears to be the case at present.
|
* THIS PROGRAM SHOWS THE EFFECT OF MOVING
* CHARACTERS (TWO ASTERISKS) TO A DYNAMIC
* VARIABLE, WITHIN THE BOUNDS OF THE
* *LENGTH.
*
DEFINE DATA LOCAL
1 #D (A) DYNAMIC
1 #A (A20) INIT <'QWERTASDFG'>
1 #LENGTH (I2)
END-DEFINE
*
INCLUDE AATITLER
INCLUDE AASETC
*
MOVE #A TO #D
*
EXAMINE #D FOR 'X' GIVING LENGTH #LENGTH
*
WRITE 5T '*LENGTH FOR #D IS: ' *LENGTH (#D) /
5T '#LENGTH FOR #D IS: ' #LENGTH
PRINT 5T 'VALUE OF #D IS:' #D / 5T '-' (30) //
*
MOVE '**' TO SUBSTRING (#D,17,2)
EXAMINE #D FOR 'X' GIVING LENGTH #LENGTH
*
WRITE 5T '-- AFTER MOVE TO SUBSTRING --' /
WRITE 5T '*LENGTH FOR #D IS: ' *LENGTH (#D) /
5T '#LENGTH FOR #D IS: ' #LENGTH
PRINT 5T 'VALUE OF #D IS:' #D / 5T '-' (30)
*
END
------------------------------------------------------
Here is the output for the program above.
PAGE # 1 DATE: 04/05/11
PROGRAM: LENGTH03 LIBRARY: SNIPPET
*LENGTH FOR #D IS: 20
#LENGTH FOR #D IS: 10
VALUE OF #D IS: QWERTASDFG
-------------------------------------------
-- AFTER MOVE TO SUBSTRING --
*LENGTH FOR #D IS: 20
#LENGTH FOR #D IS: 18
VALUE OF #D IS: QWERTASDFG **
----------------------------------------------
******************************************************
Discussion of the output above.
If you look at the output from the first "segment",
*LENGTH (#D) is twenty. Basically, this means that
#D is "sort of" like an A20 variable.
Therefore, there is no problem with the statement:
MOVE '**' TO SUBSTRING (#D,17,2)
Just pretend #D is a non-dynamic variable formatted A20.
As you can see from the second output "segment", the
two asterisks are where you would expect them to be, namely,
the 17th and 18th positions of #D.
********************************************************
Discussion of a program variation
Suppose I altered just one statement in the program LENGTH03.
Instead of the statement: MOVE '**' TO SUBSTRING (#D,17,2)
I coded MOVE '**' TO SUBSTRING (#D,22,2).
As before, after the first "segment" of the program, #D would
have *LENGTH = 20; in other words, it would behave just like an
A20 formatted non-dynamic variable.
Therefore, if I run the program, I would see the same first
segment of output namely:
PAGE # 1 DATE: 04/05/11
PROGRAM: LENGTH03 LIBRARY: SNIPPET
*LENGTH FOR #D IS: 20
#LENGTH FOR #D IS: 10
VALUE OF #D IS: QWERTASDFG
-------------------------------------------
Then, I would receive the following error message.
NAT1326 Range specified with FROM/LENGTH clause is outside field.
-------------------------------------------------------------------
TEXT:
Range specified with FROM/LENGTH clause is outside field.
EXPL:
Error in FROM/LENGTH clause of EXAMINE or SEPARATE statement:
- The FROM position is not within the field; or
- the specified LENGTH exceeds the length of the field; or
- the LENGTH value is negative.
ACTN:
Check program and correct error.
Not hard to understand the error message. #D is an A20 variable,
and I am trying to move two asterisks into the 22nd and 23rd
positions of #D. Simply will not work.
**************************************************************
Now we will look at another slight variant of LENGTH03.
* THIS PROGRAM SHOWS THE EFFECT OF MOVING
* CHARACTERS (TWO ASTERISKS) TO A DYNAMIC
* VARIABLE, OUTSIDE THE BOUNDS OF THE
* *LENGTH, BUT WITHIN THE "EXPANDED" LENGTH.
*
DEFINE DATA LOCAL
1 #D (A) DYNAMIC
1 #A (A20) INIT <'QWERTASDFG'>
1 #LENGTH (I2)
END-DEFINE
*
INCLUDE AATITLER
INCLUDE AASETC
*
MOVE #A TO #D
*
EXAMINE #D FOR 'X' GIVING LENGTH #LENGTH
*
WRITE 5T '*LENGTH FOR #D IS: ' *LENGTH (#D) /
5T '#LENGTH FOR #D IS: ' #LENGTH
PRINT 5T 'VALUE OF #D IS:' #D / 5T '-' (30) //
*
EXPAND DYNAMIC #D TO 30
*
WRITE 5T '-- AFTER EXPAND DYNAMIC --' /
WRITE 5T '*LENGTH FOR #D IS: ' *LENGTH (#D) /
5T '#LENGTH FOR #D IS: ' #LENGTH / 5T '-' (30)
*
MOVE '**' TO SUBSTRING (#D,27,2)
EXAMINE #D FOR 'X' GIVING LENGTH #LENGTH
*
WRITE 5T '-- AFTER MOVE TO SUBSTRING --' /
WRITE 5T '*LENGTH FOR #D IS: ' *LENGTH (#D) /
5T '#LENGTH FOR #D IS: ' #LENGTH
PRINT 5T 'VALUE OF #D IS:' #D / 5T '-' (30)
*
END
------------------------------------------------
What has changed in the program above? First, I
have added:
EXPAND DYNAMIC #D TO 30
*
WRITE 5T '-- AFTER EXPAND DYNAMIC --' /
WRITE 5T '*LENGTH FOR #D IS: ' *LENGTH (#D) /
5T '#LENGTH FOR #D IS: ' #LENGTH / 5T '-' (30)
*
and changed the following statement to:
MOVE '**' TO SUBSTRING (#D,27,2)
whereas in LENGTH03 the statement was:
MOVE '**' TO SUBSTRING (#D,17,2)
------------------------------------------------
Here is our output from LENGTH04 above:
PAGE # 1 DATE: 04/05/11
PROGRAM: LENGTH04 LIBRARY: SNIPPET
*LENGTH FOR #D IS: 20
#LENGTH FOR #D IS: 10
VALUE OF #D IS: QWERTASDFG
------------------------------
-- AFTER EXPAND DYNAMIC --
*LENGTH FOR #D IS: 20
#LENGTH FOR #D IS: 10
------------------------------
----------------------------------------------------
This was followed by the same NAT1326 error message
we saw above.
The reason for this last program was to demonstrate that
the EXPAND statement did not change Natural's perspective
of #D. The *LENGTH for #D after the EXPAND statement is still
20, not 30 (as can be seen above).
Time to understand what EXPAND, RESIZE and REDUCE really do.
In the buffer area where DYNAMIC variables are stored, there
are "reserved areas" for every DYNAMIC variable.
These are NOT, repeat, NOT, the same thing as *LENGTH.
Adding to a DYNAMIC variables "reserved area" simply ensures
that there is a contiguous area set aside for that variable.
This "reserved area", MAY, at a later time, DISAPPEAR. If a different
existing DYNAMIC variable, with say an *LENGTH of 72, has a text string of
length 51,837 moved to it, and if there is not a lot of room
left in the buffer area, Natural will "appropriate" reserved areas
from other DYNAMIC variable to make room for the expanded variable.
Natural will NEVER appropriate space from the *LENGTH of a DYNAMIC variable.
To repeat an earlier comment, it is *LENGTH that most resembles
a format (e.g. A500) for a non-dynamic variable.
There really is no similarity between an expanded size set via
EXPAND or RESIZE and a format for a non-dynamic variable.
A source of confusion
---------------------
Note that if you use REDUCE or EXPAND (to a smaller size), it may
seem as if the reduced size is like a format size. Not really.
What is happening is that when you specify a REDUCE size that is less than
*LENGTH, you are also changing *LENGTH. It once again is *LENGTH
which resembles the format of a non-dynamic variable.
|
|
Description :
In a previous post we saw how *LENGTH is affected by MOVE'ing
various variables and constants to a DYNAMIC variable.
To be brief, *LENGTH reflects the "current" physical size
of a DYNAMIC variable. As we noted, this size can include
trailing blanks.
By contrast, RESIZE, REDUCE, and EXPAND do not impact current
physical size, UNLESS, they specify a size smaller than the current
physical size (this can only be done via RESIZE and REDUCE).
The programs in this posting will demonstrate what *LENGTH
really indicates, and how RESIZE, REDUCE, and EXPAND may, or may
not, impact *LENGTH.
|
|
Disclaimer :
|
|
Utilities and samples shown here are not official parts of the Software AG products. These utilities and
samples are not eligible for technical support through Software AG Customer Care.
Software AG makes no guarantees pertaining to the functionality, scalability, robustness, or degree of
testing of these utilities and samples. Customers are strongly advised to consider these utilities and samples as "working examples" from which
they should build and test their own solutions
|
|
|
|
|
|
|
Post a new Code Sample
Modify this Code Sample