Exception
Handling :
Overview:
This module enables the student to
understand the concept of Exception
handling.
Outline:
Topics covered,
· Input
Specification (IPDS, IPJX, IPN)
· Data structure
· File
information data structure
· Program
status data structure
Objective:
By the end of this module, the student should be
able to:
- Data
structure
- INFDS,
INFSR and *PSSR data structure
Data Structure:
The
RPG/400 program allows you to define an area in storage and the layout of the
fields, called subfields, within the area. This area in storage is called a
data structure.
You
can use a data structure to:
- Define the same internal area multiple times using different data formats
- Operate on a field and change its contents
- Divide a field into subfields without using the MOVE or MOVEL operation codes
- Define a data structure and its subfields in the same way a record is defined
- Define multiple occurrences of a set of data
- Group non-contiguous data into contiguous
internal storage locations.
In addition,
there are three special data structures, each with a specific purpose:
- A data area data structure (identified by a U in position 18 of the data structure statement)
- A file information data structure (referred to by the keyword INFDS on a file description specifications continuation line)
- A program-status data structure (identified by an S in position 18 of the data structure statement).
Data structures can be program-described or
externally described.
Data Structure Statement Specifications
Data
structure statements are defined on the input specifications and must follow
all input specifications for records. The specifications for data structure
statements are:
Position
|
Entry
|
6
|
I
|
7-12
|
Name
of the data structure being defined. This entry is optional for a
program-described data structure, and is required for an externally described
data structure, a file information data structure (INFDS), and a data area
data structure.
|
13-16
|
Blank
|
17
|
Blank: Program-described data structure.
E:
Externally described data structure. The data structure subfields definitions
are retrieved from an externally described record format.
|
18
|
Blank: Other than a program status, data area or
initialized data structure.
I
: Globally initialized
data structure.
S : Program-status data structure.
U : Data area data structure.
|
19-20
|
DS
|
21-30
|
Blank: The data structure is program described.
Entry: This is the name of the file whose first record
format contains the field descriptions used as the subfields descriptions for
this data structure.
|
31-43
|
Blank
|
44-47
|
Blank: A single occurrence data structure.
nnnn: A number (right-adjusted) indicating the number
of occur-rences
of the data structure.
Note: This entry must be blank for a data area
data structure, a file
information data structure, and a program-status data
structure.
|
48-51
|
Length of data structure (optional). This entry must be
right-adjusted.
|
52-74
|
Blank
|
Rules for Specifying Data
Structure Statements
Remember
the following when you specify data structure statements:
- The data structure name must be a symbolic name with a maximum of six characters. The name can appear on only one data structure specification, cannot be a look ahead field, and can be specified anywhere a character field is allowed.
- All entries for one data structure and its subfields must appear together; they cannot be mixed with entries for other data structures.
- The data structure length is determined by the first specification in the program that defines a length in one of the preceding ways. Subsequent conflicting lengths are incorrect. The length of a data structure is one of the following:
- The length specified in the input-field specifications if the data structure name is an input field
- The length specified in positions 48 through 51 of the data structure statement
- The highest To position of a subfield within a data structure if the data structure name is not an input field.
- A compile-time or prerun-time array cannot be used in a data area data structure or in a multiple-occurrence data structure.
- Data structures are character data and can be from 1 to 9999 characters in length.
- A data structure and a subfield of a data structure cannot have the same name.
Special Data Structures
Special data structures include:
- Data
area data structures
- File
information data structures (INFDS)
- Program-status data structures.
Data Area Data Structure
A data
area data structure, identified by a U in position 18 of the data structure
statement, indicates to the RPG/400 program that it should read in and lock the
data area of the same name at program initialization and should write out and
unlock the same data area at the end of the program. Data area data structures,
as in all other data structures, have the type character. A data area read into
a data area data structure must also be character. The data area and data area
data structure must have the same name unless you rename the data area within
the RPG/400 program by using the *NAMVAR DEFN statement.
You
can specify the data area operations (IN, OUT, and UNLCK) and have the type for
a data area that is implicitly read in and written out. Before you use a data area
data structure with these operations, you must specify that data area in the
result field of the *NAMVAR DEFN statement. A data area data structure cannot
be specified in the result field of a PARM operation. If you specify blanks for
the data area data structure (positions 7 through 12 of the input
specifications line that contains a U in position 18), the RPG/400
program uses a local data area. To provide a name for a local data area, use
the *NAMVAR DEFN operation, with *LDA in factor 2 and the name in the result
field. If data structure name entry is blank then the local data area is used.
This
data area either you can create using CRTDTAARA command or if not created by
you then system will create it in QTEMP library at the start of job and will
delete it at the end of the job.
Following
example shows how we divide fields using subfields using Data Area Data
Structure:
Step
1:
Create
data area using CRTDTAARA command on command line and press F4:
Create Data Area
(CRTDTAARA)
Type choices, press Enter.
Data area
. . . . . . . . . . . *DTA1
Name
Library . . . . . . . . . .
. *CURLIB Name, *CURLIB
Type . . . . . . . . . . . . . . *DEC, *CHAR, *LGL, *DDM
Bottom
F3=Exit
F4=Prompt F5=Refresh F10=Additional parameters F12=Cancel
F13=How to use this display F24=More keys
Step
2:
Write
data area as ‘DTA1’ which is data area name, library name and provide data area
type *CHAR.
Data
area is having 3 types:
- Decimal (*DEC)
- Character (*CHAR)
- Logical (*LGL)
Step3: after inserting above
information press F10 to fill additional attributes like data areas length as
shown below:
Create Data Area
(CRTDTAARA)
Type choices, press Enter.
Data area
. . . . . . . . . . . > DTA1 Name
Library . . . . . . . . . . .
> PB01U010 Name, *CURLIB
Type . . . . . . . . . . . . . . > *CHAR *DEC, *CHAR, *LGL, *DDM
Length:
Length . . . . . . . . . . . . 20 1-2000
Decimal positions . . . . .
. 0-9
Initial value
. . . . . . . . .
Text 'description' . . . . . . . *BLANK
Additional
Parameters
Authority
. . . . . . . . . . .
*LIBCRTAUT Name, *LIBCRTAUT,
*CHANGE...
Bottom
F3=Exit
F4=Prompt F5=Refresh F12=Cancel
F13=How to use this display
F24=More keys
Press enter to create dta1 in library
pb01u01o.
Step
4:
Write
simple RPG program to see how Data Area DS is define or use in RPG.
To
define Data Area DS use the prompt as given below:
Columns . . . : 1 71
Edit PB01U01S/MYRPG
SEU==>
DADS1
FMT
DS .....IDsname....NODsExt-file++.............OccrLen+....................
*************** Beginning of data *************************************
0000.01 * USE IPDS PROMPT HAVING ‘U’ AT ‘OPTION’
TO DEFINE DATA AREA DS.
0001.00 IDTA1 UDS
Prompt type . . . DS
Sequence number . . .
0001.00
Data Struct External
Name Number Option
DS File Name Occurs
Length
DTA1 U DS
F3=Exit
F4=Prompt F5=Refresh F11=Previous record
F12=Cancel F23=Select prompt F24=More keys
See
the following ‘IPJ’ prompt where to define the attributes of subfield.
IPJ :
Positions
|
Name
|
Entry
|
7-42
|
Blank
|
|
43
|
Data format
|
Blank
P
B
L
R
|
44-47
|
From
|
1-9999
|
48-51
|
To
|
1-9999
|
52
|
Decimal positions
|
Blank
0-9
|
53-58
|
Field name
|
Symbolic name
|
59-60
|
Control Level
|
Blank
L1-L9
|
61-62
|
Match fields
|
Blank
M1-M9
|
63-64
|
Field record relation
|
Blank
01-99
L1-L9
MR
U1-U8
H1-H9
RT
|
65-70
|
Field indicators
|
Blank
01-99
H1-H9
U1-U8
RT
|
71-74
|
Blank
|
|
75-80
|
Comments
|
Optional
|
Columns . . . : 1
71 Edit PB01U01S/MYRPG
SEU==> DADS1
FMT
DS .....IDsname....NODsExt-file++.............OccrLen+....................
*************** Beginning of data *************************************
0000.01 * USE IPDS PROMPT HAVING ‘U’ AT ‘OPTION’
TO DEFINE DATA AREA DS.
0001.00 IDTA1 UDS
0000.10 * USE IPJ PROMPT TO DEFINE SUBFIELDS OF
DATA AREA DS.
0002.00 I 1 62AMT1
Prompt
type . . . J Sequence number . . . 0002.00
Decimal Field
Control Matching
P/B/L/R
From To
Positions Name Level Fields
1 6
2 AMT1
Field Record Positive Negative Zero /
Relation Field Field Blank
F3=Exit
F4=Prompt F5=Refresh F11=Previous record
F12=Cancel F23=Select prompt F24=More keys
Define other fields ‘AMT2’ and ‘SUM’
using same prompt ‘IPJ’ as shown below. Use *NAMVAR define data area ‘DTA1’ and
initialize values 100 and 200.20 to fields AMT1 and AMT2 respectively. Add this
amount to variable or subfield SUM.
Columns . . . : 1
71 Edit PB01U01S/MYRPG
SEU==>
DADS1
FMT
DS .....IDsname....NODsExt-file++.............OccrLen+....................
*************** Beginning of data *************************************
0000.01 * USE IPDS PROMPT HAVING ‘U’ AT ‘OPTION’
TO DEFINE DATA AREA DS.
0001.00 IDTA1 UDS
0000.10 * USE IPJ PROMPT TO DEFINE SUBFIELDS OF
DATA AREA DS.
0002.00 I 1 62AMT1
0003.00 I 7 122AMT2
0004.00 I 13 202SUM
0005.00 C *NAMVAR DEFN
DTA1
0006.00 C Z-ADD100 AMT1
0007.00 C Z-ADD200.20 AMT2
0008.00 C AMT1 ADD
AMT2 SUM
0009.00 C *LOCK OUT
DTA1
0010.00 C UNLCKDTA1
0011.00 C SUM DSPLY
0012.00 C SETON LR
****************** End of data ****************************************
F3=Exit
F4=Prompt F5=Refresh F9=Retrieve
F10=Cursor F11=Toggle
F16=Repeat find F17=Repeat change F24=More keys
Exception
or error handling:
In any
application development exception/error handling plays a very important role.
The errors can occur at any time while running the application program.
Therefore, you as a programmer should be capable of handling such errors rather
than allowing them to abnormally end the program itself. The term exception
tells about the study of various error conditions and error handling implies
detecting and correcting errors.
RPG/400
provides File Information Data Structure (INFDS), file exception/error
subroutine (INFSR), program status data structure and program exception/error
subroutine (*PSSR) for exception/error handling.
INFSR is used with *PSSR is used to find
file level exception and only program level exception are handle by Program
Status Data Structure using *PSSR.
When error code is greater than 99 then
user can able to use *PSSR routine. Other wise user have to use simple
subroutine to handle the exception.
These are some error codes which are use
to handle the error.
|
TABLE
FILE ERROR CODES
|
|
|
NORMAL
CONDITIONS
|
|
|
CODES
|
MEANING
|
|
00000
|
No exception/error occurred.
|
|
00002
|
Function key used to end display.
|
|
00011
|
End of file on a read (input).
|
|
00012
|
No record found on a CHAIN, SETGT, SETLL
operation.
|
|
00013
|
Subfile is full on a write operation.
|
|
EXCEPTION-ERROR
CONDITIONS
|
|
|
01011
|
Undefined record type (input record does
not match record-identifying indicator).
|
|
01021
|
Tried to write a record that already
exists(file being used has unique keys and key duplicate, or attempted to use
duplicate relative record number to a subfile).
|
|
01031
|
Match field out of sequence.
|
|
01041
|
Array/table load sequence error.
|
|
01051
|
Excess entries in array/table file.
|
|
01071
|
Numeric sequence error.
|
|
01121
|
No indicator on the DDS keyword for Print
Key
|
|
01122
|
No indicator on the DDS keyword for Roll
Up Key.
|
|
01123
|
No indicator on the DDS keyword for Roll
Down key.
|
|
01124
|
No indicator on the DDS keyword for Clear
Key.
|
|
01125
|
No indicator on the DDS keyword for Help
Key.
|
|
01126
|
No indicator on the DDS keyword for Home
Key.
|
|
01201
|
Record mismatch detected on input.
|
|
01211
|
I/O operation to a closed file.
|
|
01215
|
OPEN issued to a file already open.
|
|
01216
|
Error on an implicit OPEN/CLOSE
operation.
|
|
01217
|
Error on an explicit OPEN/CLOSE
operation.
|
|
01218
|
Record already locked.
|
|
01221
|
Update operation attempted without a
prior read.
|
|
01231
|
Error on SPECIAL file.
|
|
01235
|
Error in PRTCTL space or skip entries.
|
|
01241
|
Record number not found. (Record number
specified in record address file is not present in file being processed.)
|
|
01251
|
Permanent I/O error occurred.
|
|
01255
|
Session or device error occurred.
Recovery may be possible.
|
|
01261
|
Attempt to exceed maximum number of
acquired devices.
|
|
01281
|
Operation to un acquired device.
|
|
01282
|
Job ending with controlled option.
|
|
01285
|
Attempt to acquire a device already
acquired.
|
|
01286
|
Attempt to open shared file with SAVDS or
IND options
|
|
01287
|
Responses to indicators overlap IND
indicators.
|
|
01299
|
Other I/O error detected.
|
|
01331
|
Wait time exceeded for READ from WORKSTN
file.
|
|
Program status Codes
|
|
|
NORMAL CONDITIONS
|
|
|
CODES
|
MEANING
|
|
00000
|
No exception error occurred.
|
|
00001
|
Called program returns with the LR
indicator on.
|
EXCEPTION-ERROR
CONDITIONS
|
|
|
CODES
|
MEANING
|
|
00100
|
Value out of range for string operation
|
|
00101
|
Negative square root.
|
|
00102
|
Divide by zero
|
|
00121
|
Invalid array index.
|
|
00122
|
OCCUR outside of range.
|
|
00123
|
RESET attempted during initialization
subroutine.
|
|
00202
|
Called program failed, halt indicator (H1
through H9) not on.
|
|
00211
|
Program specified on CALL or FREE not
found
|
|
00221
|
Called program tried to use a parameter
not passed to it.
|
|
00231
|
Called program returned with halt
indicator on.
|
|
00232
|
Halt indicator on in this program.
|
|
00233
|
Halt indicator on when RETRN operation
run.
|
|
00299
|
RPG formatted dump failed.
|
|
00333
|
Error on DSPLY operation.
|
|
00401
|
Data area specified on IN or OUT not
found
|
|
00402
|
*PDA not valid for non-restart job.
|
|
00411
|
Data area types or lengths do not match.
|
|
00412
|
Data area not locked for output
|
|
00413
|
Errors on IN or OUT operation.
|
|
00414
|
User not authorized to use data area.
|
|
00415
|
User not authorized to change data area.
|
|
00421
|
Error on UNLCK operation
|
|
00431
|
Data area previously locked by another
program.
|
|
00432
|
Data area locked by program in the same
process.
Character field not entirely enclosed by
SO and SI.
|
|
00907
|
Decimal data error (invalid digit or
sign).
|
|
00970
|
The level numbers of the generating
compiler and the run-time subroutines do not match.
Virtual storage exceeded.
|
|
09998
|
Internal failure in RPG compiler or in
run-time subroutines.
|
|
09999
|
Program exception in system routine.
|
The following reserved words define
symbolic locations within the file information data structure (INFDS) and the
program status data structure.
- (*FILE)
- (*OPCODE)
- (*PARMS)
- (*PROGRAM)
- (*RECORD)
- (*ROUTINE)
- (*STATUS)
See the following example where we use *STATUS opcode with INFDS.
File- Information Data Structure (INFDS)
The
purpose of a file information data structure is to identify exception/error for
a file in the program. It must be unique for each file. A file
information data structure contains predefined subfields that give information
about the type of exception or error that occurred, the operation that the
program was running when the exception/error occurred and the status of various
conditions. The INFDS data structure is specified either on the file
description line itself or on a continuation line for that file on position
54-59 (option entry) and position
60-67 (here the name of entry is entry only). Option entry is used to write
INFDS keyword and field entry is used for writing the name of the file
information data structure.
Following example shows how to handle
duplicate record error.
Step 1-
Following is the Physical File.
SEU==>
EMPMST
FMT
PF .....A..........T.Name++++++RLen++TDpB......Functions++++++++++++++++++
*************** Beginning of data *************************************
0001.00 A UNIQUE
0002.00 A
R EMPMSTR
0003.00 A EMPNO 3S 0
0004.00 A ENAME 10A
0005.00 A BSAL 7S 0
0006.00 A DEPT 7A DFT('A')
0007.00 A CITY 5A DFT('PUNE')
0008.00 A K EMPNO
****************** End of data ****************************************
F3=Exit
F4=Prompt F5=Refresh F9=Retrieve
F10=Cursor F11=Toggle
F16=Repeat find F17=Repeat change F24=More keys
Following is the display file
Columns . . . : 1
71 Edit PB01U01D/MYSCR
SEU==>
MAIN
FMT
A* .....A*. 1 ...+... 2 ...+... 3 ...+... 4 ...+... 5 ...+... 6 ...+... 7
*************** Beginning of data *************************************
0000.10 A*%%TS
SD 20040928 130438
PB01U01 REL-V5R2M0 5722-WDS
0000.20 A*%%EC
0000.30 A DSPSIZ(24
80 *DS3)
0000.40 A
R MAIN1
0000.50 A*%%TS
SD 20040928 130438
PB01U01 REL-V5R2M0 5722-WDS
0000.60 A
CF03(03)
0000.70 A
3
35'INPUT'
0000.80 A 7
24'EMPNO'
0000.90 A 15
29'F3-TOEXIT'
0001.00 A EMPNO R
B 7 33REFFLD(EMPMSTR/EMPNO
PB01U01D/
0001.10 A MSG 20
O 12 33
****************** End of data ****************************************
F3=Exit
F4=Prompt F5=Refresh F9=Retrieve
F10=Cursor F11=Toggle
F16=Repeat find F17=Repeat change F24=More keys
Above is the DDS(Data description
specification) for display file and layout of this screen ‘MAIN’ is as follows.
SIMPLE INPUT SCREEN
EMPNO 999-
OOOOOOOOOOOOOOOOOOOO
F3-TOEXIT
Step 3: start with RPG.
Define physical file with information
data structure.
Columns . . . : 1
71 Edit PB01U01S/MYRPG
SEU==>
EXCEP1
FMT
FX .....FFilenameIPEAF........L..I........Device+......KExit++Entry+A....U
*************** Beginning of data *************************************
0001.00 FEMPMST
IF E DISK KINFDS DS A
Prompt type . . . FX
Sequence number . . .
0001.00
File File End of File
Filename
Type Designation File
Sequence Format
EMPMST I F E
Mode of Record
Processing
Address Type Device Continuation
DISK K
File File
Exit Entry Addition Condition
INFDS DS A
F3=Exit
F4=Prompt F5=Refresh F11=Previous record
F12=Cancel F23=Select prompt F24=More keys
Above is ‘F’ specification where we
define ‘INFDS’. We define ‘EMP’ physical file. Now we will move our control to
SR1 subroutine for that we have to write the following information in ‘IPFK’ or
‘IPFC’ prompt.
Entries to Define and Name a File
Information Data Structure.
Position
|
Entry
|
6
|
F
|
7-52
|
Blank (if the information is specified on a separate
continuation line)
|
53
|
K (indicates a continuation line)
|
54-59
|
INFDS (identifies this
data structure as the file information data structure)
|
60-65
|
Name of the file information data structure
|
Columns . . . : 1
71 Edit PB01U01S/MYRPG
SEU==>
EXCEP1
FMT
FX .....FFilenameIPEAF........L..I........Device+......KExit++Entry+A....U
*************** Beginning of data *************************************
0001.00 FEMPMST
IF E DISK KINFDS DS A
0002.00 F KINFSR SR1
Prompt type . . . FC Sequence number . . . 0002.00
External Record Number
Record Name Field Continuation Option
Entry
K INFSR SR1
F3=Exit
F4=Prompt F5=Refresh F11=Previous record
F12=Cancel F23=Select prompt F24=More keys
Now we will insert workstation file then
define data structure having name ‘DS’ using ‘IPDS’ prompt.
IPDS:
DS Specification line is broken into following parts
|
Positions
|
Name
|
Entry
|
|
1-2
|
Page
|
Page number
|
|
3-5
|
Line
|
Line number
|
|
6
|
Form type
|
1
|
|
7-12
|
Data structure name
|
Blank
Data structure name
|
|
13-16
|
|
Blank
|
|
17
|
External description
|
Blank
E
|
|
18
|
Option
|
Blank
I
S
U
|
|
19-20
|
Record identifying indictors
|
DS
|
|
21-30
|
External file name
|
External name or data
Structure
|
|
31-43
|
|
Blank
|
|
44-47
|
Occurrences
|
Blank
1-9999
|
|
48-51
|
Data structure length
|
Blank
1-9999
|
|
52-74
|
|
Blank
|
|
75-80
|
comments
|
Optional
|
Record name: Type
the external name of the record format.
Record Identifying indicators: Type a value from 01 to 99 to represent a general indicator.
Columns . . . : 1
71 Edit PB01U01S/MYRPG
SEU==>
EXCEP1
FMT
FX .....FFilenameIPEAF........L..I........Device+......KExit++Entry+A....U
*************** Beginning of data *************************************
0001.00 FEMPMST
IF E DISK KINFDS DS A
0002.00 F
KINFSR SR1
0003.00 FMAIN
CF E WORKSTN
0004.00 IDS DS
Prompt type . . . DS
Sequence number . . .
0004.00
Data Struct External
Name Number Option
DS File Name Occurs
Length
DS DS
F3=Exit
F4=Prompt F5=Refresh F11=Previous record
F12=Cancel F23=Select prompt F24=More keys
Then
insert field name ‘AA’ and ‘*STATUS’ at 52 position as shown
below using IPJX prompt.
IPJX:
Now simply insert message ‘Duplicate’ using ‘IPN’ prompt and do the coding as given below.
|
Positions
|
Name
|
Entry
|
|
Positions
|
Name
|
Entry
|
|
7-20
|
|
Blank
|
|
21-30
|
External field name
|
Field name
|
|
31-52
|
|
Blank
|
|
53-58
|
RPG field name
|
Field name
|
|
59-60
|
Control level
|
Blank
L1-L9
|
|
61-62
|
Match fields
|
Blank
M1-M9
|
|
63-64
|
|
Blank
|
|
65-70
|
Field indictors
|
Blank
01-99
H1-H9
U1-U8
RT
|
|
71-74
|
|
Blank
|
|
75-80
|
Comments
|
Optional
|
Columns . . . : 1
71 Edit PB01U01S/MYRPG
SEU==>
EXCEP1
FMT
FX .....FFilenameIPEAF........L..I........Device+......KExit++Entry+A....U
*************** Beginning of data *************************************
0001.00 FEMPMST
IF E DISK KINFDS DS A
0002.00 F
KINFSR SR1
0003.00 FMAIN
CF E WORKSTN
0004.00 IDS DS
0005.00 I
*STATUS AA
Prompt type . . . JX Sequence number . . . 0005.00
External Field Control Matching
Field Name Name Level Fields
AA
Positive
Negative Zero /
Field Field Blank
F3=Exit
F4=Prompt F5=Refresh F11=Previous record
F12=Cancel F23=Select prompt F24=More keys
Now simply insert message ‘Duplicate’ using ‘IPN’ prompt and do the coding as given below.
Columns . . . : 1
71 Edit PB01U01S/MYRPG
SEU==>
EXCEP1
FMT
FX .....FFilenameIPEAF........L..I........Device+......KExit++Entry+A....U
*************** Beginning of data *************************************
0001.00 FEMPMST
IF E DISK KINFDS DS A
0002.00 F
KINFSR SR1
0003.00 FMAIN
CF E WORKSTN
0004.00 IDS DS
0005.00 I
*STATUS AA
0006.00 I 'DUPLICATE' C MSG1
0007.00 C READ EMPMSTR 50
0008.00 C *IN03 DOWEQ*OFF
0009.00 C EE TAG
0010.00 C EXFMTMAIN1
0011.00 C 03 LEAVE
0012.00 C WRITEEMPMSTR
0013.00 C CLEARMSG
0014.00 C ENDDO
0015.00 C SETON LR
0016.00
*************************************************************
0017.00 C SR1 BEGSR
0018.00 C AA IFEQ 01021
0019.00 C MOVE MSG1 MSG
0020.00 C GOTO EE
0021.00 C ENDIF
0022.00 C ENDSR
****************** End of data
****************************************
F3=Exit
F4=Prompt F5=Refresh F9=Retrieve
F10=Cursor F11=Toggle
F16=Repeat find F17=Repeat change F24=More keys
Above example shows you how to handle the
file related error.
Now in next example see how to handle the
program related error.
Program
Exception/Errors
The exception/errors that occurred during program execution time are
known as program exception error. i.e. an error on a CALL operation code,
division by zero, Square root of a negative number etc. Therefore if you are
doing above operations in a program it’s always a good programming practice to
provide logic to handle these errors.
A
program-status data structure, identified by an S in position 18 of the data
structure statement, provides program exception/error information to the
program. You can handle these errors in
one of following ways.
- Use error indicator in position 56-57 of those operations that
allows such an entry. If error occurs than the indicator sets on. You can
determine the action to be taken by testing the indicator for on
condition.
- A program exception/error subroutine *PSSR can be used. This
subroutine will automatically receive control when a program exception
/error occurs. Information regarding the program exception/error is made
available through a program status data structure that will be described
in next section
- If the error indicator or the program exception/error
subroutine is not present than the RPG/400 default error handler handles
program exception/error.
We use a subroutine ‘*PSSR’ to handle the error, when
error occurs program starts execution of this subroutine.
*PSSR
BEGSR
-----------
-----------
-----------
ENDSR
Above is the syntax for subroutine.
So how to implement it in our program is in
the following example.
Columns . . . : 1
71 Edit PB01U01S/MYRPG
SEU==>
EXMP10
FMT
* ..... *. 1 ...+... 2 ...+... 3 ...+...
4 ...+... 5 ...+... 6 ...+... 7
*************** Beginning of data *************************************
0000.01 * PROGRAM FOR PROGRAM STATUS DS DEFINE
MESSAGE USING IPN PROMPT.
0001.00 I 'OBJECT NOT FOUND' C
MSG1
0001.01 *
DEFINE DS USING IPDS PROMPT.
0002.00 IDS2 SDS
0001.01 *
DEFINE FIELD NAME AND ‘*STATUS’ AT 52 POSITION USING IPJX.
0003.00 I
*STATUS ST
0004.00 C CALL 'RLG'
0005.00 C A TAG
0006.00 C
SETON LR
0006.01 * SUBROUTINE FOR ERROR HANDLING
0007.00 C *PSSR BEGSR
0008.00 C ST IFEQ 211
0009.00 C MSG1 DSPLY
0010.00 C GOTO A
0011.00 C ENDIF
0012.00
C ENDSR
****************** End of data ****************************************
F3=Exit
F4=Prompt F5=Refresh F9=Retrieve
F10=Cursor F11=Toggle
F16=Repeat find F17=Repeat change F24=More keys
(C)
COPYRIGHT IBM CORP. 1981, 2002.
In above example we use to find out the
whether the object of program is existing or not. If program object is exist
then ‘Call’ command execute or call that particular program. If the object of
the program does not exist then error message will gets displayed ‘Object Not
Found’. So the code for that checking is 211.
No comments:
Post a Comment