FP_NORMAL, FP_SUBNORMAL, FP_ZERO, FP_INFINITE, FP_NAN

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Defined in header <cmath>
#define FP_NORMAL    /*implementation defined*/		(since C++11)
#define FP_SUBNORMAL /*implementation defined*/		(since C++11)
#define FP_ZERO      /*implementation defined*/		(since C++11)
#define FP_INFINITE  /*implementation defined*/		(since C++11)
#define FP_NAN       /*implementation defined*/		(since C++11)

The FP_NORMAL, FP_SUBNORMAL, FP_ZERO, FP_INFINITE, FP_NAN macros each represent a distinct category of floating-point numbers. They all expand to an integer constant expression.

Constant	Explanation
FP_NORMAL	indicates that the value is normal, i.e. not an infinity, subnormal, not-a-number or zero
FP_SUBNORMAL	indicates that the value is subnormal
FP_ZERO	indicates that the value is positive or negative zero
FP_INFINITE	indicates that the value is not representable by the underlying type (positive or negative infinity)
FP_NAN	indicates that the value is not-a-number (NaN)

[edit] See also

fpclassify (C++11)	categorizes the given floating point value (function)