Re: [libvirt] proposal: allow use of "bool": HACKING: discuss C types

"Daniel P. Berrange" <berrange(a)redhat.com&gt; wrote: > On Fri, Dec 12, 2008 at 09:58:32AM +0100, Jim Meyering wrote: >> I propose to allow (encourage, even) the use of the standard C99 type, >> bool, in libvirt, but not in public interfaces[1]. There are already >> uses in cgroup.c and xmlrpc.c, as well as those in the gnulib "c-ctype.h" >> header which is included from many of libvirt's .c files. >> >> The motivation is to make the code as readable as possible. >> When you see the declaration of an "int" variable, member, or function, >> that type gives you no clue whether it is used as a boolean. If you >> see a few uses that treat it as boolean, that's still no guarantee, >> and it may be non-trivial to ensure that there isn't some non-boolean >> value with a special meaning. >> >> However, if you see a "bool" variable, you do have that guarantee. > > I don't particularly like the idea of using the bool type > > - No system header files use it Of course. Can't use it there for the same reason that we wouldn't use it in libvirt's own public interfaces, as I explained. But public interfaces make up such a small fraction of the code in question that it'd be a shame to impose its restrictions on all the rest. > - Library header files which use a boolean type have nearly all defined > their own custom bool types, not using stdbool.h and there's no guarentee > that stdbool's idea of 'true' matches the other apps' This is the same fundamental restriction. "bool" cannot be used in public headers. > - We don't use it in the public API, or on the wire for the remote > protocol, since it has undefined size. Same point. > - The GNULIB bool emulation is unable to provide equivlance between > C's idea of true (any non-zero value) and the defined 'true' > constant (whose value is 1) That sounds scary, but isn't an issue in practice. The uses of "true" and "false" are typically only for initialization. IMHO, one should never compare a bool-declared variable to "true" or "false".