See printf in the ISO C99 standard with corrigenda TC1, TC2, and TC3 included, e.g. http://www.open-std.org/JTC1/SC22/WG14/www/docs/n1256.pdf Note: common extensions (like positional args "%1$d") are not supported. This is an original implementation, written from the ground up by Markus van Dijk, while employed by Technologies88.com. No code was borrowed from any commercial and/or open source. For now, see the documentation generated by doxygen (cd to doc; make).