Why is there no isnormal / isfinite / isinf / ...?

i have a code that contains some lengthy calculations. For a certain number of loop iterations everything runs fine, but some point i get NaNs and InFs on the output. To find the bug I wanted to put checks with isnormal (from the cmath.h) but it seems as if this is not available in cint. What other function can I use to check whether a value is neither NaN nor InF ?