fpclassify
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Name

fpclassify, isfinite, isnormal, isnan, isinf — floating-point classification macros

Synopsis

#include <math.h>
int fpclassify(   x);
int isfinite(   x);
int isnormal(   x);
int isnan(   x);
int isinf(   x);
[Note] Note
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
fpclassify(), isfinite(), isnormal():
_XOPEN_SOURCE >= 600 || _ISOC99_SOURCE;
or cc -std=c99
isnan():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE || _ISOC99_SOURCE;
or cc -std=c99
isinf():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE;
or cc -std=c99
[Note] Note

Link with −lm.

DESCRIPTION

Floating point numbers can have special values, such as infinite or NaN. With the macro fpclassify(x) you can find out what type x is. The macro takes any floating-point expression as argument. The result is one of the following values:

FP_NAN

x is "Not a Number".

FP_INFINITE

x is either plus or minus infinity.

FP_ZERO

x is zero.

FP_SUBNORMAL

x is too small to be represented in normalized format.

FP_NORMAL

if nothing of the above is correct then it must be a normal floating-point number.

The other macros provide a short answer to some standard questions.

isfinite(x)

returns a nonzero value if

(fpclassify(x) != FP_NAN && fpclassify(x) != FP_INFINITE)

isnormal(x)

returns a nonzero value if (fpclassify(x) == FP_NORMAL)

isnan(x)

returns a nonzero value if (fpclassify(x) == FP_NAN)

isinf(x)

returns 1 if x is positive infinity, and −1 if x is negative infinity.

CONFORMING TO

C99

NOTES

In glibc 2.01 and earlier, isinf() returns a nonzero value (actually: 1) if x is an infinity (positive or negative). (This is all that C99 requires.)

SEE ALSO

finite(3), INFINITY(3), isgreater(3)

COLOPHON

This page is part of release 2.79 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.

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