Mathematical Functions

The macro HUGE_VAL defined in the header math.h and the macros FLT_EPSILON, FLT_MAX, FLT_MIN, DBL_EPSILON, DBL_MAX, DBL_MIN, LDBL_EPSILON, LDBL_MAX, and LDBL_MIN defined in the header float.h all refer to variables. Consequently, you cannot use these macros in places where constant expressions are required, such as in global initializations.

Note  When C99 extensions are enabled, math.h defines HUGE_VAL as a constant double representation of positive infinity.