finite, finitef, finitel, isinf, isinff, isinfl, isnan, isnanf, isnanl - BSD floating-point classification functions
#include <math.h>
int finite(double x);
int finitef(float x);
int finitel(long double x);
int isinf(double x);
int isinff(float x);
int isinfl(long double x);
int isnan(double x);
int isnanf(float x);
int isnanl(long double x);Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
The finite(), finitef(), and
finitel() functions return a nonzero value if
x is neither infinite nor a "not-a-number" (NaN) value, and 0
otherwise.
The isnan(), isnanf(), and
isnanl() functions return a nonzero value if x
is a NaN value, and 0 otherwise.
The isinf(), isinff(), and
isinfl() functions return 1 if x is positive
infinity, -1 if x is negative infinity, and 0 otherwise.
fpclassify(3)