Advanced RPG

1
Advanced RPG

• Chapter 11
• Advanced Data Definition and Manipulation

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Data Types

• (From Chapter 3)
• Character
• Numeric
• Date
• Boolean
• DBCS
• Pointer

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Data Types

• Date Types and Time defaults
• Date yyyy-mm-dd (10 byte)
• Time hh.mm.ss (8 byte)
• Timestamp yyyy-mm-dd-hh.mm.ss.mmmmmm (26
  bytes)
• Alternate displays are available
• MDY, DMY, EUR
• Set by using either DATFMT or TIMFMT keyword\
• Examples p. 232

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Data Types

• All date and time formats allow you to refer to
  them by
• YEARS (or Y)
• MONTHS (M)
• DAYS (D)
• HOURS (H)
• MINUTES (MN)
• SECONDS (S)
• MSECONDS (MS)

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Data Types

• Op Codes
• ADDDUR Allows you to add duration coded in
  Factor2 to date in Factor1, with answer going to
  result field. (If value is negative the duration
  is subtracted not added)
• Example on page 233
• SUBDUR Two uses, One to subtract a date/time
  duration (similar to ADDDUR), Second is to
  calculate the duration between two date/time
  units.

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Data Type

• Op Codes
• EXTRCT Extracts a portion of the Date, Time, or
  Timestamp and stores it in the result field.
  Factor 1 is always blank.
• Cannot use EVAL op code with the or with
  date/time fields. Must use the Add/Sub Dur op
  code.
• Also cannot determine day of week unless you
  compare it to a known Sunday. ie 12/31/1899

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Data Type

• Pointer Data Types store addresses of memory
  locations instead of the actual data located
  there.
• Tells you where to find something not what is
  stored there.
• Example P.236
• Used in the C programming language but not widely
  used in RPG!!

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Data Type

• Like (field definition)
• Defining a field length or type by referencing a
  second field that provides the definition.
  
  
  
  
  
  
  
• D NewField S LIKE(OldField)
• OldField can be another D spec or a field from a
  file.
• Can place or in the length to either add or
  subtract from the referenced size. P. 237

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Data Type

• Field Inspection
• built-in functions and operations that let you
  inspect the size and properties of data items or
  test individual positions or bytes within a
  character field.
• SIZE returns number of bytes or length of
  argument. (returns size not digits!!)
• LEN returns the number of digits or characters
  in an expression. (char-significant digits,
  numeric-precision of expression)

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Data Type

• Field Inspection
• DECPOS returns the number of decimal positions
  of a numeric variable
• ELEM returns the number of elements in an
  array or table or number of occurrences in a
  multiple occurrence data structure.
• TESTN test to see if character field contains
  all numeric characters, leading blanks or all
  blanks
• Useful in validating fields for numeric use.

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Data Type

• Field Inspection
• TEST checks the validity of date, time or
  timestamp fields.
• Must specify specific type otherwise default is
  used.
• SCAN lets you look for a character or string of
  characters within a character field.
• Direction is left to right and is case sensitive
• Found is turned on if successful
• Result field can contain position it found string
  or 0 if it does not find string

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Data Type

• Field Inspection
• SCAN nearly identical to SCAN operation, but
  lets you perfrom the scan within an expression.
• Cannot search an array or use FOUND bif
• CHECK Similar to SCAN. CHECK verifies each
  character in Factor 2 is among the valid
  characters in Factor 1 if mismatch it stores the
  location of the mismatch in result field.
• Useful for verification of a string

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Data Type

• Field Inspection
• CHECKR Works exactly like CHECK but in reverse
  order, right to left.
• Field Manipulation
• Concatenation Character String
• If result field is to large it pads with blanks
• If result field is to small it truncates on the
  right
• TRIM Trim blanks at edges
• TRIML Trim leading blanks
• TRIMR Trim trailing blanks

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Data Type

• Field Manipulation
• SUBST Extracts a character string
• Can specify starting position and length
• DEC Converts the result of an expression to a
  packed decimal format.
• XLATE lets you translate characers within a
  string to other characters.
• From and To strings must be same length

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Data Area

• Data Area Data Structure
• Defined by a U in position 23
• If no name provided it is represented by LDA
• Works similar to a file
• Loaded when program is run
• Written back to data area when program ends

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Data Areas

• Data Areas as/400 objects that represent
  storage locations used to share data between
  programs within a job or between jobs.
• Local Data Area created for each job
• 1024 positions long, type character, initially
  filed with blanks.
• when job ends lda is gone
• p.223

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Data Areas

• Can access Data Areas without defining them in D
  specs (reading into another one you do have
  specified).
• Use DATAARA in Factor1
• Result field contains variable to receive
  contents
• p. 224
• Not automatically retrieved or written back to
  external data area, you must program this.

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Data Areas

• DATAARA
• IN Retrieves a data area
• OUT Writes back to data area
• UNLOCK Unlocks data area

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Data Type

• Program Described Data Structures allow you to
  subdivide fields into smaller fields.
• P. 238
• Overlay keyword subfield overlays storage of
  another subfield
• Different way of subdividing the field.
• Used to group fields from file that are not
  adjacent. P. 239

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Data Type

• Externally Described Data Structures
• Format defined in DDS and refer to it in D specs.
• p. 240
• Multiple Occurrence Data Structures
• Structure is repeated in storage by OCCURS ()
  keyword.
• Similar to an array or table but much more
  complex collection of elements.

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Data Type

• Initializing Data Structures
• Will contain blanks at start of program unless
  you specify initialized value. (even numeric data
  types!!)
• Keyword INZ(value)
• Or use built in INZSR initialize subroutine.

23
Data Type

• File Information Data Structure
• special data structure defined for each file used
  in your program.
• Contains predefined fields that can provide
  information to your program about the file and
  I/O operations.
• Helpful in debugging
• Keyword INFDS and name of data structure on F
  spec (p. 247)

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Data Type

• File Information Data Structure
• Usefulness
• Position 1 8 File Name
• Position 16 21 contain last op code used on
  file
• Position 11 15 five-digit I/O Status code
• 00000 no error or exception
• 00002 Function key was used to end display
• 00011 signals end of file on read
• 00012 signals a no-record found condition on a
  chain
• gt 00999 error code
• 01218 indicates a locked record
• 01021 indicates attempt to write duplicate key
  record

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Data Type

• Program status data structure provide
  information about the program itself and about
  exceptions or errors that occur
• similar to file with predetermined subfields that
  automatically acquire values during execution.
• Name of Program
• Job name
• Who called it

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Data Type

• Status Codes
• 00000 no error occurred
• 00101 negative square root
• 00102 divide by zero
• 00907 decimal data error
• S in position 23 of DS definition indicates a
  Program Status Data Structure.
• p. 249

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Data Area

• Error Handling
• Without explicit error handling within your
  program, any runtime error will cause the system
  to suspend the program and send an interactive
  message to the user.
• (E) extender can be used p.249
• Causes program to ignore error and continue
• PSSR built in subroutine name that is called
  when an error occurs p. 250
• Combines file and program handling into one area.
• You can control what happens when error is
  encountered.