MI/C builtins/APIs documentation

[qsrvbas@xxxxxxxxxxxx (Tom Liotta)]

To all:

A C API that is often used is '__errno'. This API essentially returns the errno 
that results from an error encountered while calling other C APIs such as 
open() and write(). Look at the ILE RPG Sorceror's Guide Redbook and you'll see 
'__errno' referenced many times.

However, I haven't been able to locate any clear documentation from IBM that 
defines the '__errno' API. For some discussions, it seems that '__errno' could 
be thought of as an "undocumented interface". Of course, it's now used so 
pervasively that IBM would have a difficult time ever changing its interface or 
blocking it nor do I think they'd ever want to since it exists on other 
platforms and possibly is even defined within some 'standard' someplace, not to 
mention the fact that it's too valuable to interfere with.

But still, I can't find documentation. Further, there are numerous other 
builtins/functions that seem undocumented but fully available for use, once you 
know they exist. E.g., I'm looking at some code built around '_XORSTR', 
'_ORSTR' and '_ANDSTR' to do bitwise manipulation in ILE RPG. Now, technically, 
the MI instructions XORSTR, ORSTR and ANDSTR are indeed documented; but just 
because an MI instruction exists does not mean a function or builtin exists for 
it. And apparently, just because a builtin/function exists doesn't mean it's 
documented nor even that an MI instruction is available for it.

Other than a reference in a Redbook or spreading the word through a mailing 
list, how would anybody know that '__errno' is available? What about '_XORSTR'? 
or '_OPNTH1'??? How would anybody know what to do with them or even if they 
should be used?

The C/C++ Run-Time Library, C Library and MI Library manuals are very useful, 
but they don't mention '__errno'... AFAIK. What guidelines do you use to decide 
whether to use it or not?

Tom Liotta

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Tom Liotta
The PowerTech Group, Inc.
19426 68th Avenue South
Kent, WA 98032
Phone  253-872-7788 x313
Fax    253-872-7904
http://www.powertechgroup.com


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