fpclassify, isfinite, isnormal, isnan, isinf — floating-point classification macros
Synopsis
#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 versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
isinf():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 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 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.
Attributes
For an explanation of the terms used in this section, see attributes(7).
| Interface | Attribute | Value |
|---|---|---|
| fpclassify(), isfinite(), isnormal(), isnan(), isinf() | Thread safety | MT-Safe |
Conforming to
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
Colophon
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Referenced By
finite(3), INFINITY(3), isgreater(3), math_error(7), nan(3).
The man pages isfinite(3), isinf(3), isnan(3) and isnormal(3) are aliases of fpclassify(3).