макросы классификации с плавающей запятой (floating-point classification macros)
Имя (Name)
fpclassify, isfinite, isnormal, isnan, isinf - floating-point
classification macros
Синопсис (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 <= 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
Описание (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.
Атрибуты (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() │ │ │
└──────────────────────────────────────┴───────────────┴─────────┘
Стандарты (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.
Примечание (Note)
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.)
Смотри также (See also)
finite(3), INFINITY(3), isgreater(3), signbit(3)
