For some target machines, GCC supports additional options to the format attribute (Function AttributesDeclaring Attributes of Functions).
:: _solaris-format-checks:
Solaris targets support the cmn_err (or __cmn_err__) format check. cmn_err accepts a subset of the standard printf conversions, and the two-argument %b conversion for displaying bit-fields. See the Solaris man page for cmn_err for more information.
:: _darwin-format-checks:
Darwin targets support the CFString (or __CFString__) in the format attribute context. Declarations made with such attribution are parsed for correct syntax and format argument types. However, parsing of the format string itself is currently undefined and is not carried out by this version of the compiler.
Additionally, CFStringRefs (defined by the CoreFoundation headers) may also be used as format arguments. Note that the relevant headers are only likely to be available on Darwin (OSX) installations. On such installations, the XCode and system documentation provide descriptions of CFString, CFStringRefs and associated functions.