Question

I have a method that needs to do a different thing when given an unset float than a float with the value of 0. Basically, I need to check whether or not a variable has been, counting it as set if it has a value of 0.

So, what placeholder should I use as an unset value (nil, NULL, NO, etc) and how can test to see if a variable is unset without returning true for a value of 0?

Answer 1

You can initialize your floats to NaN (e.g. by calling nan() or nanf()) and then test with isnan() if they have been changed to hold a number. (Note that testing myvalue == nan() will not work.)

This is both rather simple (you will probably include math.h in any case) and conceptually sensible: Any value that is not set to a number is “not a number”…