File Management - IBM

Application program considerations for DBCS
The following sections describe considerations for writing applications that process
double-byte data.
“Designing application programs that process double-byte data”
“Changing alphanumeric application programs to DBCS application programs”
Designing application programs that process double-byte data
Design your application programs for processing double-byte data in the same
way you design application programs for processing alphanumeric data, with the
following additional considerations:
v Identify double-byte data used in the database files.
v Design display and printer formats that can be used with double-byte data.
v If needed, provide DBCS conversion as a means of entering double-byte data for
interactive applications. Use the DDS keyword for DBCS conversion (IGCCNV)
to specify DBCS conversion in display files. Because DBCS work stations
provide a variety of double-byte data entry methods, you are not required to use
the AS/400 DBCS conversion function to enter double-byte data.
v Create double-byte messages to be used by the program.
v Specify extended character processing so that the system prints and displays all
double-byte data. See “Extended double-byte characters” on page 203 for
instructions.
v Determine whether additional double-byte characters need to be defined.
User-defined characters can be defined and maintained using the character
generator utility (CGU). Information on CGU can be found in the ADTS/400:
Character Generator Utility book.
When you write application programs to process double-byte data, make sure that
the double-byte data is always processed in a double-byte unit and do not split a
double-byte character.
Changing alphanumeric application programs to DBCS
application programs
If an alphanumeric application program uses externally described files, you can
change that application program to a DBCS application program by changing the
externally described files. To convert an application program, do the following:
1. Create a duplicate copy of the source statements for the alphanumeric file that
you want to change.
2. Change alphanumeric constants and literals to double-byte constants and
literals.
3. Change fields in the file to the open (O) data type or specify the Alternative
Data Type (IGCALTTYP) DDS keyword so that you can enter both double-byte
and alphanumeric data in these fields. You may want to change the length of
the fields as the double-byte data takes more space.
4. Store the converted file in a separate library. Give the file the same name as its
alphanumeric version.
Appendix B. Double-byte character set support 211