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).

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.)

COLOPHON

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