A quick Google search for "AVR sprintf progmem" came up with a reference to sprintf_P() which expect the formatting string to be in PROGMEM. You can even format strings from PROGMEM using the %S format specifier instead of %s.
A quick Google search for "AVR sprintf progmem" came up with a reference to sprintf_P() which expect the formatting string to be in PROGMEM. You can even format strings from PROGMEM using the %S format specifier instead of %s.