HUGE_VAL

From Cppreference

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Defined in header <cmath>
#define HUGE_VAL /*implementation defined*/

The HUGE_VAL macro expands to a positive double constant expression. It indicates that the value is not representable by the double type (infinity). The constant is not necessarily representable as a float.

[edit] See also

HUGE_VALF (C++11)	indicates value too big to be representable (infinity) by float (macro constant)
HUGE_VALL (C++11)	indicates value too big to be representable (infinity) by long double (macro constant)