Mapping File I/O Feedback Data Structures
A map of the INFDS can be used to simplify program code.
IBM offers a mechanism for RPG application program to access system database file information. The file information data structure (INFDS), must be unique for each file and defined in the same scope as the file. For global files, the INFDS must be defined in the main procedure. For files local to a subprocedure, the INFDS must be defined in the Definition specifications of the subprocedure. Furthermore, the INFDS must be defined with the same storage type, automatic or static, as the file it is associated with.
Externally Defined INFDS
A simple way of defining a data structure is to reference an external file description. The DDS below describes the fields of the PSDS for use in any RPG program. Making a map of the PSDS standardizes defining the DS subfields in RPG programs. Adopting the map as a standard means that all programs using the external map are coded to respond to the same field names. This makes it easy to interpret the code when it is time to maintain a program.
****************************************************************
* File Name - ISIDBFDS *
* *
* Function - This was designed to serve as an external *
* data structure to define the file information *
* data structure for database files. *
* *
* Programmer - Steve Croy *
****************************************************************
****************************************************************
* Modification log *
* *
* Date Programmer Description *
* *
****************************************************************
A R RISIDBF TEXT('Database INFDS')
A DBFNAM 8 COLHDG('File' 'Name')
A DBFOPN 1 COLHDG('File' 'Open')
A DBFEND 1 COLHDG('File' 'End')
A DBFSTS 5S 0 COLHDG('File' 'Status')
A DBCODE 6 COLHDG('RPG' 'OPCODE')
A DBRRTN 8 COLHDG('RPG' 'Routine')
A DBRSTM 8 COLHDG('RPG' 'Statement')
A DBRNAM 8 COLHDG('Record' 'Format')
A DBPMSG 7 COLHDG('CPF' 'Msg ID')
A DBPINS 4 COLHDG('PGM' 'Instruction')
A DBF001 14 COLHDG('Undefined')
A DBFINP 2S 0 COLHDG('Input')
A DBFOUT 2S 0 COLHDG('Output')
A DBFMOD 2S 0 COLHDG('Mode')
A DBF002 4 COLHDG('Undefined')
A DDFODP 2 COLHDG('ODP' 'Type')
A DBXNAM 10 COLHDG('External' 'File Name')
A DBFLIB 10 COLHDG('File' 'Library')
A DBF003 22 COLHDG('Undefined')
A DBFLEN 4B 0 COLHDG('Record' 'Length')
A DBF004 2 COLHDG('Undefined')
A DBFMBR 10 COLHDG('File' 'Member')
A DBF005 8 COLHDG('Undefined')
A DBFTYP 4B 0 COLHDG('File' 'Subtype')
A DBF006 7 COLHDG('Undefined')
A DBFRCD 8B 0 COLHDG('Record' 'Count')
A DBFACC 2 COLHDG('Access' 'Type')
A DBFDUP 1 COLHDG('Allow' 'Dupe')
A DBFSRC 1 COLHDG('Source' 'File')
A DBUFCB 10 COLHDG('User' 'FC' 'Blk')
A DBFBOV 10 COLHDG('FC' 'Blk' 'Ovr')
A DBF007 27 COLHDG('Undefined')
A DBFOST 4B 0 COLHDG('DBF' 'Open' 'Sts')
A DBFLAG 1 COLHDG('File' 'Flags')
A DBOPID 2 COLHDG('Open' 'ID')
A DBMAXR 8B 0 COLHDG('Max' 'Records')
A DBF008 177 COLHDG('Undefined')
A DBRRN# 8B 0 COLHDG('Relative' 'Record')
A DBF009 112 COLHDG('Undefined')
Using the Mapped DS
The code snippett below illustrateS using the INFDS. The indicated the data structure is named DBFBK. This example from IBM provides a glimpse of the information available using the database specific INFDS.
DCL-F MYFILE DISK(*EXT) INFDS(DBFBK);
DCL-DS DBFBK;
FDBK_SIZE INT(10) POS(367); // Current line num
JOIN_BITS INT(10) POS(371); // JFILE bits
LOCK_RCDS INT(5) POS(377); // Nbr locked rcds
POS_BITS CHAR(1) POS(385); // File pos bits
DLT_BITS CHAR(1) POS(384); // Rcd deleted bits
NUM_KEYS INT(5) POS(387); // Num keys (bin)
KEY_LEN INT(5) POS(393); // Key length
MBR_NUM INT(5) POS(395); // Member number
DB_RRN INT(10) POS(397); // Relative-rcd-num
KEY CHAR(2000) POS(401); // Key value (max size 2000)
END-DS;
The INFDS can be a valuable debugging tool. Having the data structued defined can show the compiler information which tells a software engineer file member used and the relative record number could aid debugging the code.