isnormal (3) Linux Manual Page
fpclassify, isfinite, isnormal, isnan, isinf – floating-point classification macros
Synopsis
#include <math.h>Link with -lm.
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():
- _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.