fpclassify(3)              Library Functions Manual              fpclassify(3)

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

LIBRARY
       Math library (libm, -lm)

SYNOPSIS
       #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
       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 (),    | Thread safety | MT-Safe |
       |isnan (), isinf ()                          |               |         |
       +--------------------------------------------+---------------+---------+
STANDARDS
       C11, POSIX.1-2008.

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

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

Linux man-pages 6.7               2023-10-31                     fpclassify(3)