On 27.03.2021 00:16, Valery Ushakov wrote:
On Sat, Mar 27, 2021 at 00:01:25 +0100, Roland Illig wrote:
To me, writing 'sizeof expr' is clearer than 'sizeof(expr)' since
'sizeof' is not a function, same as with 'return'.
Did I misinterpret the style guide in this regard?
We do want it to look like a function call (and so the usual style
rules for the function call apply). Think of cases where it's used as
a subexpression, e.g.
sizeof(expr) + 4
The parentheses of a function call expression have highest precedence
and bind to the left. The parentheses to the right of the sizeof
operator do not bind at all though. Therefore I find it misleading to
write them like in a function call.
The following code demonstrates why I prefer to omit the parentheses
around the argument to the 'sizeof' operator:
#include <stdio.h>
int
main(int argc __attribute__((__unused__)), char **argv)
{
/* misleading since it looks like a function call */
printf("%zu\n", sizeof(argv)[3]);
/* parentheses make the precedence unambiguous */
printf("%zu\n", sizeof((argv)[3]));
/* a space removes the confusion about precedence */
printf("%zu\n", sizeof (argv)[3]);
/* without any parentheses, spacing equals precedence */
printf("%zu\n", sizeof argv[3]);
/*
* If the parentheses to the right of 'sizeof' had the same
* precedence as function call parentheses, this artificial
* code could be written without the outer pair of parentheses.
*/
printf("%c\n", (sizeof(argv))["0123456789"]);
#if 0
/*
* If 'sizeof' were a function returning size_t, this code
* would compile.
*/
/* error: array subscript is not an integer */
printf("%c\n", sizeof(argv)["0123456789"]);
#endif
}
It was fun to find out that there actually _is_ a case where the
different precedence matters. At first I had thought that the whole
discussion would be academic anyway.
Roland
