printf format

[root]

In the back of my mind, it seems like I read that there is a format
character used in printf(C) that allows the formatting of numbers.
I'd like to take a number, ie. 123456.78 and print it as
123,456.78 .  If this info is in the manual (SCO), I can't find it or
it is not written clearly enough to say that what it does.

If printf does not have this ability, it should be added.  

thanks in advance....
Scotty
{ames,rutgers,texsun,smu}!attctc!ozdaltx!sysop