[Bug c/57647] lvalue required as increment operand

[Bug c/57647] lvalue required as increment operand

[mpolacek at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57647

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mpolacek at gcc dot gnu.org

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
While 4.7 issues warning: value computed is not used, 4.8 and 4.9 do not for
int
main ()
{
  char bar = 4;
  char *foo = &bar;
  (unsigned long *)foo++;
  return 0;
}

For 4.7, you can just add cast to void
(void) (unsigned long *)foo++;
to silence the warning.

[Bug c/57647] lvalue required as increment operand

[vijunag at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57647

--- Comment #2 from vijay Nag <vijunag at gmail dot com> ---
(In reply to Marek Polacek from comment #1)
> While 4.7 issues warning: value computed is not used, 4.8 and 4.9 do not for
> int
> main ()
> {
>   char bar = 4;
>   char *foo = &bar;
>   (unsigned long *)foo++;
>   return 0;
> }
> 
> For 4.7, you can just add cast to void
> (void) (unsigned long *)foo++;
> to silence the warning.

Does it work only for int or any type ?

[Bug c/57647] lvalue required as increment operand

[mpolacek at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57647

--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
It should work for any type, but, why don't you do only foo++;, i.e. drop the
cast?  In that case there shouldn't be value computed is not used warning.

[Bug c/57647] lvalue required as increment operand

[vijunag at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57647

--- Comment #4 from vijay Nag <vijunag at gmail dot com> ---
(In reply to Marek Polacek from comment #3)
> It should work for any type, but, why don't you do only foo++;, i.e. drop
> the cast?  In that case there shouldn't be value computed is not used
> warning.

Pointer Arithmetic.
I want to advance the pointer by sizeof(unsigned long) but not by sizeof(char).

[Bug c/57647] lvalue required as increment operand

[schwab@linux-m68k.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57647

--- Comment #5 from Andreas Schwab <schwab@linux-m68k.org> ---
((unsigned long*)foo)++ and ((unsigned long *)foo++) are not equivalent
expressions.  The former is the same as foo = (char *)((unsigned long*)foo +
1), the latter is foo += sizeof(*foo) (and the cast has no effect).

[Bug c/57647] lvalue required as increment operand

[vijunag at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57647

--- Comment #6 from vijay Nag <vijunag at gmail dot com> ---
(In reply to Andreas Schwab from comment #5)
> ((unsigned long*)foo)++ and ((unsigned long *)foo++) are not equivalent
> expressions.  The former is the same as foo = (char *)((unsigned long*)foo +
> 1), the latter is foo += sizeof(*foo) (and the cast has no effect).

((unsigned long*)foo)++ is no longer a valid C expression for the cast
evaluates it to be an R-value rather than L-value

[Bug c/57647] lvalue required as increment operand

[vijunag at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57647

--- Comment #7 from vijay Nag <vijunag at gmail dot com> ---
(In reply to vijay Nag from comment #6)
> (In reply to Andreas Schwab from comment #5)
> > ((unsigned long*)foo)++ and ((unsigned long *)foo++) are not equivalent
> > expressions.  The former is the same as foo = (char *)((unsigned long*)foo +
> > 1), the latter is foo += sizeof(*foo) (and the cast has no effect).
> 
((unsigned long*)foo)++ is no longer a valid C expression for the cast
evaluates it to be an R-value rather than L-value.  Why is the second
expression
evaluating as foo += sizeof(*foo) ? ()(parentheses) comes before ++(postfix)
although they both have the same precedence  but associativity is from left to
right.

[Bug c/57647] lvalue required as increment operand

[schwab@linux-m68k.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57647

--- Comment #8 from Andreas Schwab <schwab@linux-m68k.org> ---
Postfix operators bind stronger than cast operators.  If you need help on the C
language then bugzilla is not the right place.

[Bug c/57647] lvalue required as increment operand

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57647

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID

--- Comment #9 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Seems there's nothing to do here.