To the best of my knowledge, printf (and sprintf) will never truncate a field that is too long for the width specified in the format string -- it will always provide each field with as many characters as needed to fit a given string with "%s" or all digits with "%d", or all digits to the left of the decimal point with "%f", thereby screwing up the programmer's intended vertical alignment of fields on successive lines, rather than eliminate significant data that would not have fit the programmer's margins.

update: thanks to PodMaster for some much needed tutoring... my comments above did not consider format specs that really do impose field truncation, like "%1.1s" -- I was only thinking of the more common flavor, like "%1s", which does not truncate. (I still don't know how to truncate numerics...)