Re: [avr-gcc-list] Deprecated warning on 3.4.1

[Harald Kipp]

At 09:05 05.08.2004 +0200, David Brown wrote:
> Such casts should certainly issue a warning, as they could easily lead to
> problems, at least on other processors.  Suppose you are using a processor
> which requires 16-bit data to be aligned properly, and src is a pointer to
> such data (unsigned short*).  Then the ((unsigned char *) src)++ expresion
> leaves "src" with a value that is illegal for its type - not a good thing to
> do.  In general, the effect to arithmetic (like ++) on a variable is
> dependand on its exact type, so messing with that type is a bad plan.

I fully understand this, but...



> I would say that a better way to write such code would be to introduce a new
> local variable of type (unsigned char*), initialised to src.  You can then
> use the new pointer freely.

In some cases this may introduce additional code, which
can break the application. Remember, we are not talking about
PCs, but embedded systems, where portability is not always
the main focus. Instead developers often count the number of
machine cycles. Thus, it's not "OK, let's use another local
variable for free." In my case it is bootloader code, where
every byte counts and portability is absolutely no issue.

Nevertheless I understood now, that this compiler warning
makes sense.

Thanks,

Harald