fpclassify(3) Library Functions Manual fpclassify(3)
NAME
fpclassify, isfinite, isnormal, isnan, isinf - floating-point classifi-
cation macros
LIBRARY
Math library (libm, -lm)
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():
_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
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 nor-
mal 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 nega-
tive infinity.
ATTRIBUTES
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() │ │ │
└────────────────────────────────────────────┴───────────────┴─────────┘
STANDARDS
C11, POSIX.1-2008.
HISTORY
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.)
NOTES
For isinf(), the standards merely say that the return value is nonzero
if and only if the argument has an infinite value.
SEE ALSO
finite(3), INFINITY(3), isgreater(3), signbit(3)
Linux man-pages 6.9.1 2024-05-02 fpclassify(3)
Generated by dwww version 1.16 on Tue Dec 16 04:25:43 CET 2025.