if you mean the ansi C stdlib then there isn't, theres no sleep, or delay.
N794 so its a little older but its not in newer versions either.
http://www.vmunix.com/~gabor/c/draft.html
you might be mistaking an add on sleep function added by an os or a compiler suite.
MS's version of sleep does pretty much the same as what i posted, last time i checked it.
[edit]
I rechecked MS's version of sleep which is _sleep, its basically a wrapper that calls Sleep, first checking to see if its a zero argument and then incrementing it.
often with MS's VC functions since they are quite often just ever so slightly different they add an _ but just as often theres a #define to set sleep to _sleep