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   isinf    ( 3 )

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Имя (Name)

fpclassify, isfinite, isnormal, isnan, isinf - floating-point
       classification macros

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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

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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.

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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()                      │               │         │
       └──────────────────────────────────────┴───────────────┴─────────┘

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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.

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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.)

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Смотри также (See also)

finite(3), INFINITY(3), isgreater(3), signbit(3)

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