errm, i think they were both released with the first version of the ANSI C Language.
Btw: i nominate you for the most uninteresting post on the general discussion board so far :D
YEAH WOO PHEAR THE UNINTERESTING POST
It's a little known fact that I finished writing stdio.h the day after I wrote stdlib.h ;)
Same time: both were released in 1987.
Alk ANSI persons.. or ask K & R ..