I have a problem which sounds similar. My code looks roughly like this: . . #include <math.h> . . uint8_t test; isnan(test); . The error I get is "No matching function call to isnan". For more context, the reason I'm chasing this down is because I'm using the PCL library and Xcode is giving me compile errors which seem to have this as their root cause. I've tried adding the "Foundations" framework, which someone suggested somewhere, but that didn't help. I've tried adding "/usr/bin/gcc" to my header search paths, but that hasn't worked either. Any ideas or suggestions would be great. Thanks!