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 at-
tributes(7).
┌────────────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├────────────────────────────────────────────┼───────────────┼─────────┤
│fpclassify(), isfinite(), isnormal(), │ Thread safety │ MT-Safe │
│isnan(), isinf() │ │ │
└────────────────────────────────────────────┴───────────────┴─────────┘
STANDARDS
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.
NOTES
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.)
SEE ALSO
finite(3), INFINITY(3), isgreater(3), signbit(3)
Linux man-pages 6.03 2023-02-05 fpclassify(3)
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