SIMPLE SOLUTIONS

# FPCLASSIFY(3) - man page online | library functions

Floating-point classification macros.

Chapter
2015-08-08
```FPCLASSIFY(3)                       Linux Programmer's Manual                       FPCLASSIFY(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);

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 expres‐
sion 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(),    │ Thread safety │ MT-Safe │
│isnormal(), isnan(), isinf() │               │         │
└─────────────────────────────┴───────────────┴─────────┘
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.)