99% ACK

Prefer unsigned for flags-type variables...

Some reason not to use an enum type? :p

You cannot OR enum type elements together without them degenerating to an integer type, I think.

GCC doesn't warn about it, at least.

@sipa is correct. Storage class for enum is 'int', unless greater size is needed (int -> unsigned int -> long -> unsigned long -> etc., IIRC)

Indeed, you can define flags using an enum, but you can't use the enum as parameter when you want to be able to specify multiple flags as it's no longer an enumeration. I believe Qt has a 'typesafe flags' type but that doesn't help us here :) I do think defining the flag values using an enum has a nicer syntax than a list of const XXX.

And I agree with @jgarzik that it's better to have anything that you manipulate bitwise be unsigned. It steers clear of crazy undefined areas of C++, such as overflows flipping the sign bit.

This might work, too, IIRC:

enum my_foo_bits {
    FLAG_FOO = (1U << 0),
    FLAG_BAR = (1U << 1),
};

@laanwj Nice I observed the same problem with the client interface pull we are working on ^^. We should then change to unsigned int there, too, right?

@luke-jr: GCC warns about OR 2 enum flags, when the function parameter is expected to be an enum ;), tried it.

Yes, it applies there too :)

Updated.

ACK

Comments from @jgarzik are not in, so it would be nice if @sipa could update to these last 4 suggestions before this should get merged IMO.

Updated.