I found quite_NaN and it seems to work well - i'm surprised there is no "isnan" function included though!
you can write a simple one though
bool isnan(double x)
which utilizes the fact that NaN's are not equal to anything, even themselves.
I have a big grid of numbers that I am reading in, but sometimes instead of a number i get a "blank" that i need to put something in to recognize that there was infact nothing there. How else would I do that without nan's if the possible values of these numbers range from -inf to inf?