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

Why? Because it is the generally accepted recommendation - as stated
by Jon Paris as follows in his "Who Knew You Could..." redbook:


Then I disagree with Jon.

I have the utmost respect for Jon Paris. He's a guru's guru. However, theidea that his statements are infallible is absurd.

There are errors in that redbook. A few months ago I was looking for anexample of the Qp0lProcessSubtree() API, and found an example in thatredbook. I thought my problems were solved until I looked at the code.There are several things being done in that code that make no sense, andaccomplish nothing -- there were some points that the author clearlydidn't understand.

But, the redbook has still been a tremendous, tremendous benefit to theRPG community on the whole. And that's my point, you can be valuablewithout being 100% right about every detail.

In this case, it's something of the matter of an opinion. C programmersexpect errno to be unchanged unless an error occurs. That's gospel tothem. When you change it, you break that rule. Some programs rely onthat feature. (Although, you could certainly argue that they shouldn't --the fact is, some do.)

Now you're reading this and probably saying to yourself "but, the Cprograms won't be affected, I'm changing it in my RPG code, not theirprograms!". Maybe. As long as you know for certain that your RPGprograms will never be called by C programs. Or from other RPGprogrammers like me who expect errno to work the way it does from C.

Of course, you may think your programs aren't ever going to be called byanother program, and that you're therefore safe -- but -- how do you knowwhat'll happen to your code in the future? 5 years from now? 10 yearsfrom now?

And when it becomes a habit to clear errno, will you remember when you'rewriting your service programs or utility programs that you shouldn't clearit there?

Not clearing it, and not expecting it to be cleared, are good habits toget into. In my opiion, they're the right way to do things, and I hopeI've made my case so that you understand why.

Unfortunately, there are a few oddball C routines that only use errno toreport errors -- they're far and few between -- but if you run into one ofthem then you MUST clear errno, or you won't be able to determine if theyfailed. In that circumstance, you shoudl save the original value oferrno before clearing it, and restore that value afterwards.