The message formatting functions (see Messaging) all write output according to format strings similar to those used by the standard ‘printf’ function. Libretto also has several other functions which perform formatted output, as well as a number of functions which perform formatted input. For these functions, all formatting escapes provided by the ANSI standard are translated, as are a number of extensions. There is also an ongoing attempt to accommodate the extensions mandated by the draft ISO standard for C9x. The precise nature of the conversions allowed is currently in flux, owing to apparent conflicts between the GNU extensions and the ISO C9x extensions. This issue will be resolved in a later release. At the moment, I document only one ‘printf’ extension over ANSI/ISO C89:
While there may be other extensions at the moment, they are not yet documented, and should therefore not be used.