Re: Can I Trust Pointer Arithmetic In Re-Allocated Memory?

"Bill Reid" <hormelfree@xxxxxxxxxxxxxxxx> writes:
Keith Thompson <kst-u@xxxxxxx> wrote in message
news:lny7tuvrj4.fsf@xxxxxxxxxxxxxxxxxx
[...]
Mmmmm, well it's actually a C++ package (with a lot of "Object Pascal"
crap laying around apparently just in a vain attempt to create a Microsoft
style monopoly--three guesses who made it), and I do call back and
forth between C and C++ and D----i, so maybe I DO want to keep
the "unneeded" casts...

If you have a genuine need to compile the same code as both C and C++,
that's a valid reason to cast the result of the *alloc() functions.

Very very few people have such a genuine need. We can count the ones
we've seen here on the fingers of P.J. Plauger's right hand (and even
that's overkill).

C++ provides mechanisms for interfacing to C code. Unless you're
providing a library to be used with either C or C++ code, you're
probably better off picking a language for each piece of your program
and using the appropriate compiler for it.

[...]

How about if I call it from C++ like you mentioned about malloc()?
I believe I actually do call malloc() in some xxx.cpp files...

Why? C++ has "new" and "delete". But in any case, C++ is a different
language, and comp.lang.c++ down the hall on the left, just past the
water cooler.

[...]

Yes, it works with a cast. It also works without a cast, and there's
just no reason to use one.

What you quoted above is not *the* documentation for qsort(). You'll
find that in the C standard, and it doesn't say anything about casting
arguments.

Again, might be the C++ thing, or an urban legend or something...

The Solaris man page has similar wording.

[...]

Oh, while I've got you here, here's another issue I noticed that I'm
not sure about concerning realloc(). Here's the NON-documentation:

Syntax

#include <stdlib.h>
void *realloc(void *block, size_t size);

...

If block is a NULL pointer, realloc works just like malloc.

...

I read this years ago, and thought "Great, I don't necessarily have to
malloc something first, I can use realloc in a loop and the first pass
through the loop it'll just be like malloc."

Yes. If it doesn't work that way, your implementation is broken.
(But that's an unlikely bug, since the behavior is clearly documented
in the standard.)

Problem is, it didn't seem to work out that way, and I'm not sure
what I did wrong, but I think I tried a number of things, such as
explicitly initializing my memory pointer to NULL, and always got
an error...is it actually possible to use realloc() to act like malloc
with a NULL pointer?

Yes. I can't guess why you were unable to get it to work.

--
Keith Thompson (The_Other_Keith) kst-u@xxxxxxx <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.
.

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