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HP-UX 11i Version 3: February 2007

Technical documentation

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isnan() — floating-point test for NaN


#include <math.h>

int isnan( floating-type x);


The isnan() macro determines whether its argument is a NaN. The argument must be of floating type. For HP Integrity servers, the argument can be any floating type. For PA-RISC, the argument must be either double or float.

The isnan() macro implements the isnan() functionality recommended by the IEEE-754 standard for floating-point arithmetic.

The isnan() macro replaces the isnan() and isnanf() functions, which are obsolete and are no longer supported.


To use the isnan() macro, compile either with the default -Ae option or with the -Aa and -D_HPUX_SOURCE options. Make sure your program includes <math.h>. Link in the math library by specifying -lm on the compiler or linker command line.


The isnan() macro returns a nonzero value if and only if its argument has a NaN value. The macro raises no floating-point exceptions.


No errors are defined.


Take certain actions if x is not a NaN:

#include <math.h> /*...*/ double x; /*...*/ if (!isnan(x)) /*...*/


isnan(): ISO/IEC C99

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