Eivind LM wrote:
On Tue, 24 Feb 2009 15:13:55 +0100, Tom St Denis
<tstdenis@xxxxxxxxxxxxxxxx> wrote:
Eivind LM wrote:
It does of course depend on each case whether a warning is easy to
avoid or not, and also if it warns about a real problem or not. But
in any case, a warning can help me write code that more surely will
do what I intend. For example the following code is not doing what I
intended:
#include <stdio.h>
void print(int a) { printf("%d\n", a); };
int main() { print(2.5); return 0; };
I think the problem in the code is both easy to avoid and serious,
but I get no warning with -Wall and -Wextra (g++ 4.3).
That's because it's not undefined behaviour. "default" warnings
should be for things that are not guaranteed to have a known meaning
or behaviour.
I think the warning should be part of -Wall, but I understand if you
don't agree. Anyway this is not my point. I trust someone has good
reasons for the selection of warnings included in -Wall.
Because warnings for things that have defined behaviour [and aren't
specifically likely to be wrong] are annoying, see "splint" for examples
of useless warnings.
int a;
if (a == 4) { ... }
Is undefined behaviour since a is unitialized.
Compiling this example with -Wall and -Wextra gives me no warning with
g++ (Debian 4.3.2-1.1) 4.3.2. Installed by apt-get today from Debian
repositories.
You have to turn on the optimizer for the warning to come out (otherwise
the compiler can't detect it's uninitialized).
float a;
a = 0;
if (a == 4) { ... }
Is fine, but I should also point out "4" is an integral type that is
converted to float for the purpose of the expression "a == 4" . So
by your logic, it should also generate a warning.
Yes, I would like a warning if I compare a float to an int.
Why? It's perfectly valid (well yeah not the == bit, but try a > 4).
I would probably not compare two floats on equality anyway, but if I
really had to, then I would write "4" as 4.0f.
You should learn about type promotion.
That's like saying
long a;
a = 3;
Should be a warning since I didn't write 3L or (long)3.
-Wall should really just enable every warning that has something to
do with behaviour that is not predictable.
Fine, but the name should be changed.
I dunno, there are a lot of people who use -Wall -W and rely on the fact
that the warnings it produces are USEFUL not just chatty.
Tom
