isnan(3) — Linux manual page


FPCLASSIFY(3)             Linux Programmer's Manual            FPCLASSIFY(3)

NAME         top

       fpclassify, isfinite, isnormal, isnan, isinf - floating-point classi‐
       fication macros

SYNOPSIS         top

       #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
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
               || _XOPEN_SOURCE
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* Glibc versions <= 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) !=

       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

       │Interface                    Attribute     Value   │
       │fpclassify(), isfinite(),    │ Thread safety │ MT-Safe │
       │isnormal(), isnan(), isinf() │               │         │

CONFORMING TO         top

       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         top

       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         top

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

COLOPHON         top

       This page is part of release 5.09 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

                                 2017-09-15                    FPCLASSIFY(3)

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