HOT TIPS: Debugging (4 Tips)

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Data Structure Debugging

Using the debugging function, you can view all the different occurrences of a multiple-occurrence data structure (in addition to the occurrence that is currently set by the program), if you have the Object Definition Table (ODT) number of the multiple-occurrence data structure in question. There are two ways to get the ODT number of the data structure:

The first way is to compile the program with the generation options (GENOPT) parameter specified with *LIST and *XREF to get an Intermediate Representation Program (IRP) listing and a cross-reference of the IRP. For example:

 CRTRPGPGM PGM(pgmlib/pgm) SRCFILE(srclib/srcfile) + GENOPT(*LIST *XREF) 

Within the IRP cross-reference section, near the bottom of the listing under the column titled "ODT Name," find the entry for the multiple-occurrence data structure that you wish to view. It will be followed by another entry with the same name but with a suffix of zero. Appearing in front of this entry is a four-character hexadecimal number-this is the ODT number.

The other method is to dump the program object to a spool file using the DMPOBJ command as shown:

 DMPOBJ OBJ(library/program) OBJTYPE(*PGM) 

Scan the listing for the name of the multiple-occurrence data structure using the scan function. In front of the name of the data structure will be the definition of a field of the same name with a suffix of zero. Look in the hexadecimal portion of the listing on the same line to find the hexadecimal representation of this field, and find the eight characters that immediately precede the field. The first four characters in the group of eight are the ODT number.

Once you have the ODT number, you can view all the occurrences of the multiple- occurrence data structure by entering a slash followed by the ODT number for the Program Variable (PGMVAR) parameter of the Add Breakpoint (ADDBKP) or Display Program Variable (DSPPGMVAR) statement. For example:

 ADDBKP STMT(12500) PGMVAR('/0098') 



Test Programs Without Updating Files

The Inhibit Write (INHWRT) parameter on the OVRDBF command can be used to prevent records from being written, deleted or updated in a database file. The INHWRT parameter allows you to test a program without updating the database. You need to specify the following statement for any update or output files used by the programs you want to test.


Use SEU to Check Compiler Errors

Use the following technique to find errors in an RPG compile listing. After an unsuccessful compile, start SEU, press F15 (Browse/Copy), select option 2 for the first parameter (Selection) and press Enter. SEU will display the spooled file on a split screen just like it does when you include a source member. From the bottom screen, key in FIND *ERR, F *ERR or *ERR followed by F16 on the SEU command line and press Enter. Each error message will be displayed on the bottom of the screen. You can press help for second-level text on each message.

Breaking an Active Program out of a Loop

If a program is caught in an infinite loop and observability has not been removed, it may be possible to break the loop without canceling the program. Use DSPJOB OPTION(*PGMSTK) to determine the program, its library and a statement within the loop that is being executed. Use Start Service Job (STRSRVJOB), then Start Debug (STRDBG) and Add Breakpoint (ADDBKP) to set a breakpoint within the loop. When the breakpoint is displayed, press F10 to go to a command entry screen, use the Change Program Variable (CHGPGMVAR) command to set the conditions necessary for the loop to end.