#715 SDCC should throw a warning on sizeof (void).
hello
I found, that is impossible to cast the type of pointer when I want to increment it.
When I try something like this:
void *voidptr;
((unsigned int *)voidptr)++;
I got the error: 'lvalue' required for '++' operation.
If I omit the parenthesis, no increment is done because no type casting is done (because the priority of operands) and the size of void is 0.
If I try to add the sizeof of unsigned int:
ptr+=sizeof(unsigned int);
nothing happens, because in the sdcc the size of void is 0.
I think that this is not right. In this case is impossible to modify an void pointer. The gcc thinks that size of void is 1, so voidptr+=sizeof(something) makes sense.
I thing, that sizeof anything may not be 0. sizeof(void), increment void* etc may produce an error or something, but does not silently ignore it. My opinion is that the right way is make it 1, like makes gcc.
Logged In: YES
user_id=203539
The only problem is that SDCC should throw a warning on sizeof (void).
From Marc Nijweide <nijweide AT xs4all.nl> 2001-09-10, sdcc-devel,
discussion of bug #460185:
sizeof(void) is an invalid expression. sizeof is not
allowed on void expressions, it is neither 0 nor any
other value. That gcc decides that sizeof(void)=1
is a gcc extension to the ANSI C language, they know
it and supply a flag to turn of this feature.... Also pointer
arithmetic on void pointers does have its conceptual flaws
as void pointers are intended to be used when the function
is not allowed or does not need to make assumptions about
the type the pointer is pointing too.
See also:
http://www.lysator.liu.se/c/rat/c3.html#sizeof-3-3-3-4
Logged In: YES
user_id=756222
The main problem is, that is impossible to cast another type of pointer on void pointer when I try to increment it. See the first paragraph of my original message. The sizeof(void) is only secondary problem.
Logged In: YES
user_id=203539
Oh, sorry, yes you're right. I filed a 2nd bug report #905167,
because these are 2 different problems.
Logged In: YES
user_id=635249
Incrementing a casted object is not legal C (since casts are
not lvalues); both of your examples are depending on gcc
extensions. Instead of:
((unsigned int *)voidptr)++;
use:
voidptr = (unsigned int *)voidptr + 1;
Logged In: YES
user_id=756222
Thanx for the idea. But ((unsigned int *)voidptr)++; is so beautiful :-) And all
C compilers that I've seen allows it.
Logged In: YES
user_id=888171
Fixed: SDCC 2.4.4 #833 generates a warning