ctype header in 10.8

When I try to compile anything with #include <ctype>, g++ says it's not available. I tried running it through Xcode as well as opposed to the shell to no avail. Xcode actually marks it as an error in the editor. I just upgraded to OS X 10.8 and Xcode 4.4, but I don't know if this was available in OS X 10.7.4 or an earlier version of Xcode.

Any idea where I could find this so I can install it?