Re: [C400-L] DB2 UDF written in C

[Simon Coulter <shc@xxxxxxxxxxxxxxxxx>]

On 22/03/2005, at 8:53 AM, Stephen More wrote:

> I have not gotten it to work yet, but I think I may have found the  
> answer:
>
> http://www-1.ibm.com/servers/enable/site/porting/iseries/overview/ 
> faq_files.html
>
> In ILE, when I tried fopen(), fclose(), etc. on IFS stream files in
> QOpenSys they do not seem to work, but the low level calls do not have
> any problems. Is there any difference in these two types of calls?
>
> Yes. The two types of calls are different in the ILE environment. The
> calls like fopen(), fclose(), fread() work on the database files
> whereas low-level calls like open(), close(), read() work on the
> stream files. The low level calls can work on the database files by
> specifying the full qualified name (i.e. /qsys.lib/< library>.lib/<
> file>.file/< mbr>.mbr). Calls like fopen(), fclose, and fread() can
> also work on the stream files in QOpenSys if *IFSIO is specified for
> "System Interface Option" on CRTCMOD command. Once the program is
> created with *IFSIO option absolute or relative path names can be
> specified with fopen(), fclose() etc calls. However, after specifying
> *IFSIO these call will not work on the native database file system
> even if fully qualified path name is specified.

This is normal behaviour and is described in the C Programmers Guide.

The default behaviour of the fopen(), fread(), etc. functions is to map  
C stream file concepts over OS/400 record files. This is done for  
historical reasons because stream files did not exist in OS/400 when C  
was first released on OS/400. This actually has very limited use  
because most OS/400 data files are database files with a record  
oriented structure.

If you need to process stream files and database files in the same  
program then you have a few approaches:
	1) Put stream file functions in one module and compile with  
SYSIFCOPT(*IFSIO). Put the non-stream file functions in a different  
module and compile normally. Bind both modules into the same program.
	2) Use the Unix stream file functions (open, read, write, close) for  
stream file processing and reserve fopen() etc. for non-stream file  
processing. You can mix them both in the same program.
	3) Use SYSIFCOPT(*IFSIO) for stream file processing and use the record  
I/O functions (i.e., those that start with _R like _Ropen()) for  
database access. These are more like traditional OS/400 database  
functions anyway and support all the normal things like sequential read  
and write, keyed reads, record positioning, record updates, and keyed  
deletes.

I've not done it but I think you can use the Unix stream file functions  
to process flat files in QSYS.LIB file system.

Regards,
Simon Coulter.
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