#R:duke:-363700:ihlpf:18400003: 0:290 ihlpf!dap1 Nov 1 16:17:00 1983 printf uses /usr/include/varargs.h to handle variable number of arguments. On our machine, this has #ifdef's to bracket off macros for various types of machine. It's NOT done in machine language, but rather depends on the structure of the stack and the passing conventions on the machine.