On 02/10/2014 05:10 PM, Laine Stump wrote: >> >> AC_CHECK_DECLS unconditionally defines the variable to either 0 or 1, so >> checking if it is defined will still fail to compile on older headers >> that lack the enum; > > Well, it would have compiled successfully, but compiled the wrong code :-) > >> what you want is to check that it has a non-zero value. > > Now that I've seen this, it bugs me that all HAVE_* #defines aren't > consistent about this - some are undefined if the capability is missing, > and some are #defined, but to 0.
It's historical baggage of autoconf - the various checks were written at different times, but autoconf can't change the older checks to always define the macro because of back-compat. The general rule of thumb is HAVE_DECL_ is always defined, any other HAVE_ is likely undefined if the feature is missing. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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