numeric_limits question

[crei]

I was wondering what the equivalent to

numeric_limits<double>::infinity()
numeric_limits<double>::quiet_NaN()
numeric_limits<double>::signaling_NaN()

would be in C.

I have tried

#include <float.h>
isinf (DBL_MAX + 1)

and many other variants with no success.

I would also rather use a macro or a function rather than doing something
like

isinf (exp (100000))

Regards,

crei