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NAME | SYNOPSIS | DESCRIPTION | ATTRIBUTES | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
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FPCLASSIFY(3) Linux Programmer's Manual FPCLASSIFY(3)
fpclassify, isfinite, isnormal, isnan, isinf - floating-point
classification macros
#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 <= 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
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.
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│fpclassify(), isfinite(), isnormal(), │ Thread safety │ MT-Safe │
│isnan(), isinf() │ │ │
└──────────────────────────────────────┴───────────────┴─────────┘
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.
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.)
finite(3), INFINITY(3), isgreater(3), signbit(3)
This page is part of release 5.13 of the Linux man-pages project.
A description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
2021-03-22 FPCLASSIFY(3)
Pages that refer to this page: finite(3), INFINITY(3), isgreater(3), nan(3), math_error(7)
Copyright and license for this manual page
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