Re: socket api question - is it possible for recv() to receive 0byte from server? -- RPG400-L

The error reporting machinery centered about the setting of errno is
generally regarded with tolerance at best.  It requires a
``pathological coupling'' between library functions and makes use of
a static writable memory cell, which interferes with the construction
of shareable libraries.


Amen to that!

I hate it when people use global variables and IMPORT/EXPORT variables.They interfere with the modular process. and that's really all "errno"is... it's a global variable exported from a service program (when theysay "library" they mean service program, for those who may not be familiarwith Unix terminology)

"3 The value of errno is zero at program startup, but is never set to
zero by any library function.170) The value of errno may be set to
nonzero by a library function call whether or not there is an error,
provided the use of errno is not documented in the description of the
function in this International Standard."

This is what I was talking about in my previous message. C programsexpect errno to remain the same. You have to make adjustments for theenvironment, though. It says "program starttup" above, but on the Systemi, it's actually "activation group startup".

And when it says "never set to zero by any library function" it meansthat it's never set to zero by any API that you call. You should followthis standard too! Don't change it! Your programs may end up being usedas APIs someday.

"170) Thus, a program that uses errno for error checking should set
it to zero before a library function call, then inspect it before a
subsequent library function call. Of course, a library function can
save the value of errno on entry and then set it to zero, as long as
the original value is restored if errno's value is still zero just
before the return."

In my opinion, if I haven't yet made it clear (and I think I have) is thatyou should always treat your code as if it's part of a library function.(To use the terminology used in the quoted paragraph.) IF it isn't onetoday, it might be one tomorrow. We should be writing modular, reusablecode, and if we're doing that, we want to make sure we don't muck with thevalue of errno.

Remember, the C programming language is not new, it's more than 30 yearsold. Like RPG, a lot of the old programs were written in a monolithicfashion. The standard you're quoting is from 1989! Today, we should bewriting modular code.

Vern, even if you're not new to using errno, I suspect that a lot of thepeople reading this message are -- I just don't want them to learn badhabits!