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).
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)
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