Re: int a = a (Was: Bart's Language)

On 20/03/2025 10:02, Tim Rentsch wrote:

scott@slp53.sl.home (Scott Lurndal) writes:

I would disagree with this last statement.  (void)x is genuinely
useful and has no ill side effects.   'int a = a;' is exactly
the opposite - not useful and has potenial bad side effects.

 I concur except that I recommend using (void)&x rather than (void)x,
because (void)&x is safer.  If x is volatile qualified, for example,
the expression (void)x actually does something, and must not be
compiled away, whereas (void)&x does not have these properties.

I would recommend knowing which variables are volatile and which are not, so that the issue does not arise.
Casting a volatile variable to void does "something", but what that "something" is is implementation-defined and can vary between compilers.   Doing things to volatiles other than clear, simple reads or writes is a risk - the semantics are not fully defined in the C standards, implementations vary, and it is not at all uncommon for implementations to be inconsistent or buggy in that area.  This is why C++ has deprecated many uses of volatile objects.  So if you actually want to read a volatile variable but ignore the results (as you might well want to do for hardware device registers), it's best to do :
auto dummy = volatile_var;
(void) dummy;
rather than
(void) volatile_var;