_XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or
cc -std=c99

isnan():

_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or
cc -std=c99

isinf():

_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or
cc -std=c99

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 positive infinity or negative 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, POSIX.1.

For
isinf(),
the standards merely say that the return value is nonzero
if and only if the argument has an infinite value.

NOTES

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

This page is part of release 3.27 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/.