enum type int or unsigned int?

[kar1107]

Hi all,

Can the compiler chose the type of an enum to be signed or unsigned
int? I thought it must be int; looks like it changes based on the
assigned values. Below if I don't initialize FOO_STORE to be, say -10,
I get a warning about unsigned comparison and I'm seeing an infinite
loop.

If I do initialize FOO_STORE = -10, I don't see any warnings. No
infinite loop.

Isn't the type of FOO_xyz required to be an 'int'?
Can the compiler choose its type to be unsigned int?

--------
#include <stdio.h>

typedef enum {
FOO_STORE , /* if = -10 is added, no warnings. works fine */
FOO_HASHTABLE,
FOO_STATE,
FOO_CONFIG,
FOO_MAX
} foo_subobj_type _en;
int main(void) {
foo_subobj_type _en sub_obj;

for (sub_obj = FOO_MAX-1; sub_obj >= FOO_STORE; --sub_obj) {
printf("%d\n", sub_obj);
}
return 0;
}

gcc --version gcc (GCC) 3.2.3 20030502 (Red Hat Linux 3.2.3-52)
gcc -Wall -W -ansi -pedantic enum.c enum.c: In function `main':
enum.c:15: warning: comparison of unsigned expression >= 0 is always
true

Thanks,
Karthik

[Michael Mair]

CBFalconer schrieb:

Chris Torek wrote:

... snip ...

The absolute guaranteed method is a "test at bottom" style loop,
for which C lacks a convenient construct. If it had one, it might
read:

for_until_test_ at_bottom (sub_obj = FOO_MAX - 1;
sub_obj == FOO_STORE; --sub_obj) {
...
}

I strongly disagree. That is the purpose of the do loop:

do {
/* whatever */
} while (appropriate);

I am not sure whether you understood Chris Torek's point;
sub_obj = InitValue + 1;
do {
--sub_obj;
....
} while (!(sub_obj == FOO_STORE));
is not exactly convenient; if the starting point (InitValue)
were FOO_MAX instead of FOO_MAX - 1, and FOO_MAX coincided with
sub_obj's type maximum, then the addition of one would not be
possible and you'd need
sub_obj = InitValue;
first = 1;
do {
if (!first)
--sub_obj;
else
first = 0;
....
} while (!(sub_obj == FOO_STORE));
which is not exactly convenient. Of course, you still can express
everything with every kind of loop (plus some stuff). In this
case, tricks with the for loop continuation condition may lead to
cleaner code than the do--while variant. ("first || !(sub_obj ==
FOO_STORE)")
Cheers
Michael
--
E-Mail: Mine is an /at/ gmx /dot/ de address.