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(), isnan(), isinf()                                           │ Thread safety │ MT-Safe │
       └─────────────────────────────────────────────────────────────────────────────────────────────────┴───────────────┴─────────┘

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

Linux man-pages 6.03                                         2023-02-05                                               fpclassify(3)