isnormal3
Floating-point classification macros
Part of fpclassify(3).
Usage
#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():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
isnan():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| _XOPEN_SOURCE
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
isinf():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
Library
Math library (libm, -lm)
Overview
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 |
Notes
For isinf(), the standards merely say that the return value is nonzero if and only if the argument has an infinite value.
Releases
12 releases since Debian 3.1 (Sarge); the text changed 11 times.