INFINITY, NAN, HUGE_VAL, HUGE_VALF, HUGE_VALL - floating-point constants

       The macro INFINITY expands to a float constant representing positive infinity.

       The  macro  NAN  expands to a float constant representing a quiet NaN (when supported).  A quiet NaN is a
       NaN ("not-a-number") that does not raise exceptions when it is used in arithmetic.   The  opposite  is  a
       signaling NaN.  See IEC 60559:1989.

       The  macros  HUGE_VAL,  HUGE_VALF, HUGE_VALL expand to constants of types double, float, and longdouble,
       respectively, that represent a large positive value, possibly positive infinity.

       C99.

       On a glibc system, the macro HUGE_VAL is always available.  Availability of the NAN macro can  be  tested
       using  #ifdefNAN, and similarly for INFINITY, HUGE_VALF, HUGE_VALL.  They will be defined by <math.h> if
       _ISOC99_SOURCE or _GNU_SOURCE is defined, or __STDC_VERSION__ is defined and has a value  not  less  than
       199901L.

       Math library (libm)

       INFINITY, NAN, HUGE_VAL, HUGE_VALF, HUGE_VALL - floating-point constants

fpclassify(3), math_error(7)

Linux man-pages 6.9.1                              2024-05-02                                        INFINITY(3)

       C11.

#define_ISOC99_SOURCE      /* See feature_test_macros(7) */
       #include<math.h>INFINITYNANHUGE_VALHUGE_VALFHUGE_VALL