FPCLASSIFY

Section: Linux Programmer's Manual (3)
Updated: 2017-09-15
Index Return to Main Contents
 

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);

Link with -lm.

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
 

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).
InterfaceAttributeValue
fpclassify(), isfinite(), isnormal(), isnan(), isinf() Thread safetyMT-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 4.15 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/.


 

Index

NAME
SYNOPSIS
DESCRIPTION
ATTRIBUTES
CONFORMING TO
NOTES
SEE ALSO
COLOPHON

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Time: 19:42:01 GMT, September 18, 2018