On 13/06/2008, at 11:48 PM, Lim Hock-Chai wrote:
Thanks Barbara. I simplified my function to make it easier for me to
ask the question. The actual function prototype looks like below:
typedef char *logECD_STP3_piModuleName_T;
typedef char *logECD_STP3_piLocationID_T;
typedef char *logECD_STP3_piLogMessage_T;
typedef int logECD_STP3_piByteRcv_T;
typedef char *logECD_STP3_piDataRcv_T;
decimal(15,0) logECD_STP3(
logECD_STP3_piModuleName_T moduleName,
logECD_STP3_piLocationID_T locationID,
logECD_STP3_piLogMessage_T logMessage,
const logECD_STP3_piByteRcv_T *byteRcv,
const logECD_STP3_piDataRcv_T *dataRcv);
If you're simply using typedef to provide names for char* then I
wouldn't bother. Your original approach of using typedef to describe
fixed-length data values is better although weird from a C
programmer's perspective because the language (and therefore most C
programmers) has no concept of fixed-length variables. AT least with
the structures there is a length involved whereas char* has no length.
logECDSTP3 is actually a RPG export procedure and the RPG prototype
for
logECD_STP3 looks like below:
P logECD_STP3...
P B export
D pi 15 0
D piModuleName * options(*string) value
D piLocationID * options(*string) value
D piLogMessage * options(*string) value
D piByteRcv 10i 0 options(*nopass :*omit) const
D piDataRcv * options(*nopass :*omit)
D const
The c program is casting the UAM (<= Data from recv()) and passing
it to
the 5th parameter of logECD_STP3. The 4th parameter tell logECD_STP3
how long the 5th parameter is.
C passes everything except arrays by VALUE. RPG defaults to passing
everything by REFERENCE. Embed in your mind the following mantra:
Passing a pointer by VALUE is the same as passing a variable by
REFERENCE.
Therefore you can have a C prototype that passes pointers (addresses)
into an RPG prototype that accepts fixed-length variables. For example:
void rpgProc( const char * msgId );
char * msgId = "CPF1234"; /* char msgId[7] works too as long as you
strip 0x00*/
rpgProc( msgId );
D rpgProc PI
D msgId 7 CONST
c is really fun.
You have a strange idea of fun :)
It is not very programmer friendly language though.
No it's not. It's basically a high-level assembler. It requires the
programmer to play compiler while writing code (to avoid stupidities)
rather than concentrating on the task at hand. C itself is fairly
useless--it is is the library functions that make it useful. See how
far you get writing a program if you have no #include statements for
stdlib.h, stdio.h, string.h, etc.
As someone else noted C is perhaps the only mainstream programming
language where a successful compile is no indication the program will
even run. At least with COBOL, RPG, PL/1, Java, Smalltalk, Basic,
etc. as long as you are a competent programmer with a reasonably
clear idea of what you want to do a successful compile indicates your
program will do at least 80% of what you intended.
Not sure how this language can be so successful till this day. :)
Three primary reasons:
1) Because it was given away free to Universities
2) Because it supported advanced (for it's time) concepts such as
local variables, functions/procedures, prototyping, etc. Useful when
teaching programming.
3) Because people stick with what they know. For most programmers C
is the first "real" language they learn. CompSci courses spend a lot
more time on C than other languages. If C is the first language you
learn you think it's fine because you don't know any better. Once a
language reaches a certain critical mass it's hard to avoid it simply
because there is such a large code base in use.
C is fine for low-level systems code--it's rubbish for business
applications.
Regards,
Simon Coulter.
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