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You are here: manpages

FPCLASSIFY

Section: Linux Programmer's Manual (3)
Updated: 2010-09-20
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():

: _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.)

COLOPHON

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/.