Linux manual pages Section 3  

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():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
isnan():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE || /* Since glibc 2.19:
*/ _DEFAULT_SOURCE || /* Glibc versions <= 2.19:
*/ _BSD_SOURCE || _SVID_SOURCE
isinf():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19:
*/ _DEFAULT_SOURCE || /* Glibc versions <= 2.19:
*/ _BSD_SOURCE || _SVID_SOURCE
[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 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.

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value
fpclassify(), isfinite(), isnormal(), isnan(), isinf() Thread safety MT-Safe

CONFORMING TO

POSIX.1-2001, POSIX.1-2008, C99.

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.)

SEE ALSO

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

COLOPHON

This page is part of release 4.07 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man−pages/.


  Copyright 2002 Walter Harms (walter.harmsinformatik.uni-oldenburg.de)

%%%LICENSE_START(GPL_NOVERSION_ONELINE)
Distributed under GPL
%%%LICENSE_END

This was done with the help of the glibc manual.

2004-10-31, aeb, corrected