 <p>I was able to get the <code>tgmath.h</code> functions to work by including the header at the top of my PCH file.</p> <p>At some point (read: Xcode update) I had to start disabling Modules to get this to work. The details of such are in the <a href="http://stackoverflow.com/questions/23333287/tgmath-h-doesnt-work-if-modules-are-enabled">question</a> Dima links to below.</p>