On 18Jan2016 21:07, ALAN GAULD <alan.ga...@btinternet.com> wrote:
On 18/01/16 20:43, Cameron Simpson wrote:
The + modes are deceptively appealing but they are full of dangers
for precisely the reasons you have discovered(*). You very rarely
need them and you are better opening/closing the file and
using explicit modes to read/write.
But if he wants to mix the modes, he certainly should be experimenting. Having
a file open for read and write is sometimes useful; I do it myself in certain
circumstances.
Yes and so have I. Maybe twice in 30 years of programming.
It's sometimes necessary but it's much, much harder to get
right and very easy to get wrong, usually with data corruption
as a result.
I may have done it a little more than that; I agree it is very rare. I may be
biased because I was debugging exactly this last week. (Which itself is an
argument against mixed rerad/write with one file - it was all my own code and I
spent over a day chasing this because I was looking in the wrong spot).
So for a beginner I would never encourage it. For an
experienced programmer sure' if there is no other option
(and especially if you have fixed size records where
things get easier).
Tip for new players: if you do any .write()s, remember to do a .flush() before
doing a seek or a read
That's exactly my point. There are so many things you have
to do extra when working in mixed mode. Too easy to treat
things like normal mode files and get it wrong. Experts
can do it and make it work, but mostly it's just not needed.
Yes. You're write - for simplicity and reliability two distinct open file
instances are much easier.
Disagree. As far as his question goes, "wb+" is a correct mode for what he is
trying. Whether it is a sensible approach depends very much on what he is doing
with his files.
I'm not sure we know what he(?) is trying.
We only know he successfully overwrote his data and
that apparently was not his intention. There are use
cases where it makes sense but in most cases you can
get by just fine without.
Yeah. I think I was more narked by your not answering his "is wb+ correct"
literally; it may be only rarely the reasonable course, but for what he was
actually _asking_ wb+ is correct. He may not be doing the best design but as
you say we don't know his actual use case.
For the narkiness I apologise.
Cheers,
Cameron Simpson <c...@zip.com.au>
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