fpclassify(3) — Linux manual page

fpclassify(3)           Library Functions Manual           fpclassify(3)

NAME         top

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

LIBRARY         top

       Math library (libm, -lm)

SYNOPSIS         top

       #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         top

       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         top

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

STANDARDS         top

       C11, POSIX.1-2008.

HISTORY         top

       POSIX.1-2001, C99.

       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.)

NOTES         top

       For isinf(), the standards merely say that the return value is
       nonzero if and only if the argument has an infinite value.

SEE ALSO         top

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

Linux man-pages 6.04           2023-03-30                  fpclassify(3)

Pages that refer to this page: finite(3),  INFINITY(3),  isgreater(3),  nan(3),  math_error(7)

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