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ISNAN(3) Library Functions Manual ISNAN(3) NAME isnan - test for not-a-number LIBRARY Standard C Library (libc, -lc) SYNOPSIS #include <math.h> int isnan(real-floating x); DESCRIPTION The isnan() macro determines whether its argument x is not-a-number ("NaN"). An argument represented in a format wider than its semantic type is converted to its semantic type first. The determination is then based on the type of the argument. RETURN VALUES The isnan() macro returns a non-zero value if the value of x is a NaN. Otherwise 0 is returned. SEE ALSO fpclassify(3), isfinite(3), isinf(3), isinff(3), isnanf(3), isnormal(3), math(3), signbit(3) IEEE Standard for Binary Floating-Point Arithmetic, Std 754-1985, ANSI. STANDARDS The isnan() macro conforms to ISO/IEC 9899:1999 ("ISO C99"). CAVEATS On VAX the isnan() function always returns 0, as the architecture doesn't support NaN. NetBSD 8.99.34 September 27, 2017 NetBSD 8.99.34