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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | ATTRIBUTES | STANDARDS | HISTORY | NOTES | SEE ALSO | COLOPHON |
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fpclassify(3) Library Functions Manual fpclassify(3)
fpclassify, isfinite, isnormal, isnan, isinf - floating-point
classification macros
Math library (libm, -lm)
#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
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(), │ Thread safety │ MT-Safe │
│ isnormal(), isnan(), isinf() │ │ │
└──────────────────────────────────────┴───────────────┴─────────┘
C11, POSIX.1-2008.
POSIX.1-2001, C99.
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.)
For isinf(), the standards merely say that the return value is
nonzero if and only if the argument has an infinite value.
finite(3), INFINITY(3), isgreater(3), signbit(3)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
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⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
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⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
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⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
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Linux man-pages 6.15 2025-05-17 fpclassify(3)
Pages that refer to this page: finite(3), INFINITY(3), isgreater(3), nan(3), math_error(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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