"Not all of the new C99 features are supported in the versions of gcc distributed with open source operating systems. However, a sufficient number are now widely available, so you can start looking seriously at adopting C99 features in new development, especially where they make a substantial difference in efficiency or clarity.
"This article reviews the availability of C99 language and library features on recent releases of Linux and BSD. Because many of these features are standard features of gcc, a recent version of gcc will do the same thing on most other platforms. Library support, of course, varies from one distribution to another, or from one operating system to another..."
