as400 interview questions and answers-Part 16


1. What is EXTPGM in RPGLE? Give example of EXTPGM in rpgle.

 

Ans:

 

o   EXTPGM

This keyword is used in case of prototyping. So first of all we will go through the concept of prototyping.

 

ü Prototyping

·         A prototype tells the compiler how the parameters of a called program or procedure are defined.

 

·         Prototyping makes the compiler to verify that whatever parameters that will be passed to a called program or procedure appropriately defined.

 

·         Prototyping benefit us by showing the error at compile time rather than at run time.

 

ü Case1: Program without prototyping

Here, there is one rpgle program SENDPGM which calls a CL program ‘MSGSFLCL’ with parameters MSGID(7), MSGF(10) and MSGOPT(1).

 

Calling Program SENDPGM

 


Columns . . . :    1  71           Browse                       AMIT/QRPGLESRC
SEU==>                                                                SENDPGM
FMT **  ...+... 1 ...+... 2 ...+... 3 ...+... 4 ...+... 5 ...+... 6 ...+... 7
*************** Beginning of data *************************************
 
* SEND MSG0001 FROM MESSAGE FILE CPF9898 TO PROGRAM MESSAGE QUEUE
 
C                   MOVEL     'MSG0001'     MSGID
C                   MOVEL     'AM_MSGF'     MSGF
C                   MOVE      'I'           MSGOPT
C                   EXSR      SEND
C     SEND          BEGSR
C                   CALL      'MSGSFLCL'
C                   PARM                    MSGID             7
C                   PARM                    MSGF             10
C                   PARM                    MSGOPT            1
C                   ENDSR

 

Message ID . . . . . . . . . :   MSG0001                              
Message file . . . . . . . . :   AM_MSGF                              
  Library  . . . . . . . . . :     AMIT                                
Message text . . . . . . . . :   THE ACCOUNT NUMBER CAN NOT BE BLANK  

 

 

 

Called program MSGSFLCL

 


Columns . . . :    1  71           Browse                       AMIT/QRPGLESRC
SEU==>                                                                MSGSFLCL
FMT **  ...+... 1 ...+... 2 ...+... 3 ...+... 4 ...+... 5 ...+... 6 ...+... 7
*************** Beginning of data *************************************
0001.01    PGM        PARM(&MSGID &MSGF &MSGOPT)
0002.00    DCL        VAR(&MSGID) TYPE(*CHAR) LEN(7)
0003.00    DCL        VAR(&MSGF) TYPE(*CHAR) LEN(10)
0004.00    DCL        VAR(&MSGOPT) TYPE(*CHAR) LEN(1)
0006.00
0007.00
0008.00    IF         COND(&MSGOPT *EQ 'I') THEN(SNDPGMMSG +
0009.00               MSGID(&MSGID) MSGF(&MSGF))
0010.00
0011.00    IF         COND(&MSGOPT *EQ 'C') THEN(RMVMSG PGMQ(*PRV +
0012.00                 (*)) CLEAR(*ALL))
0013.00 ENDPGM
****************** End of data ****************************************

 

 

When we run the program SENDPGM then at runtime it checks if the parameters are appropriately passed or not. If we change PARM “MSGID” to some other data type or change its length, we will get the error but not at compile time. We will get the error at run time and our program cannot continue further.

 

To make sure that the program doesn’t crash at run time, we detect the error at compile time itself by using prototyping. This is depicted in Case2 below.           

 

 

 

ü Case2: Program with prototyping

To use prototyping, we do the following modifications in the calling program SENDPFM.

 

Here we have changed the Parameter MSGID’s length from 7 TO 3.

 


Columns . . . :    1  71           Browse                       AMIT/QRPGLESRC
SEU==>                                                                SENDPGM
FMT **  ...+... 1 ...+... 2 ...+... 3 ...+... 4 ...+... 5 ...+... 6 ...+... 7
 
DMSGID            S              3     >>>> Parm MSGID’s length changed from 7 to 3
DMSGF             S             10
DMSGOPT           S              1
DMSGSFLCL         PR                  EXTPGM('MSGSFLCL')
DMSGID                           7
DMSGF                           10
DMSGOPT                          1
* SEND MSG0001 FROM MESSAGE FILE CPF9898 TO PROGRAM MESSAGE QUEUE
C                   MOVEL     'MSG0001'     MSGID
C                   MOVEL     'AM_MSGF'     MSGF
C                   MOVE      'I'           MSGOPT
C                   EXSR      SEND
C     SEND          BEGSR
C                   CALLP     MSGSFLCL(MSGID:MSGF:MSGOPT)
C                   ENDSR

 

Now when we compile the program, we get the below error at compile time.

 

**Error: The type and attributes of the parameter do not match those of the prototype.

 

But the error that we have got here is at compile time that is what we wanted.

 

 

2. How to use EXPORT and IMPORT keyword in rpgle?

Ans:

o   EXPORT & IMPORT

 

Export  indicates that the variable has been defined (stored) in this module and will be used by some other module which is importing this variable using Import keyword.

 

Import  indicates that the variable has been defined (stored) in some other module and will be used here.

 

Example:

 


Columns . . . :    6  76            Edit                        AMIT/QRPGLESRC
SEU==>                                                                 MODULE1
FMT H  HKeywords++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
*************** Beginning of data *************************************
0001.00 HOPTION(*NODEBUGIO)
0002.00 DVAR1             S              5  0 EXPORT  INZ(11111)
0003.00 DVAR2             S              5  0 IMPORT
0003.03 C                   CALLB     'MODULE2'
0003.04 C                   EVAL      VAR1=VAR2 +33333  >>>>>>>>>>>>>>>   VAR2=55555
0005.00 C     VAR1          DSPLY
0006.00 C                   SETON                                        LR
****************** End of data ****************************************


 

 


Columns . . . :    6  76            Edit                        AMIT/QRPGLESRC
SEU==>                                                                 MODULE2
FMT D  DName+++++++++++ETDsFrom+++To/L+++IDc.Keywords+++++++++++++++++++++++++
*************** Beginning of data *************************************
0002.00 DVAR1             S              5  0 IMPORT
0003.00 DVAR3             S              5  0 IMPORT
0003.07 DVAR2             S              5  0 EXPORT
0003.08 C                   CALLB     'MODULE3'
0004.00 C                   EVAL      VAR2=VAR1+VAR3   >>>>>>>>>>>>>>>   VAR2=22222
0005.00 C                   RETURN
****************** End of data ****************************************


 

         


Columns . . . :    6  76           Browse                       AMIT/QRPGLESRC
SEU==>                                                                 MODULE3
FMT D  DName+++++++++++ETDsFrom+++To/L+++IDc.Keywords+++++++++++++++++++++++++
*************** Beginning of data *************************************
0002.00 DVAR3             S              5  0 EXPORT
0004.00 C                   EVAL      VAR3=11111     >>>>>>>>>> VAR3=11111
0004.01 C                   RETURN
****************** End of data ****************************************

 

 

CRTPGM PGM(AMIT/PGM1) MODULE(AMIT/MODULE1 AMIT/MODULE2 AMIT/MODULE3)

 

Below picture depicts the data flow due to import/export:






 

 







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