On 28-Mar-2012 12:18, Michael Witten wrote:
Wow, that was thorough!
The behavior of b++ vs. b-- was interesting, but is yet one more reason
why the warning is needed. Since
b-- is equivalent to !b, and b++ is equivalent to 1, if that action is
intended, there is no reason to
use either the increment or decrement operators on a bool.
gcc -std=c99 -pedantic -Wall -O0 -fdump-tree-gimple d.c
That's a trick worth knowing. Thanks!
Ran that on a test program and in every case but one there was an
implicit
(int) b
on sections of code which I though should generate warnings. (Math ops
on bools, comparison operations of
bool with ints.) The one exception in that little program was:
b=2;
which came out as
b=1;
In that case the compiler must have performed an implicit
1 = (bool) 2
Also these forms all generated implicit int conversions
if(b==1)
if(b==2)
if(b==0)
whereas
if(b)
did not.
So let's turn this around. If the compiler warned on all implicit
conversions of bool <-> int,
what program lines would it warn on that it shouldn't? It would warn
on:
if(b==1)
if(b==0)
but I would argue that line is inappropriate for a bool type, and
should be written as:
if(b)
With two bool variables, this also did not generate an implicit
conversion (and so would not warn,
which is appropriate):
if(b1 || b2)
Whereas this less preferred form would have generated an implicit (int)
[and a well deserved warning]
if(b1 + b2)
Regards,
David Mathog
mat...@caltech.edu
Manager, Sequence Analysis Facility, Biology Division, Caltech
