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
 | 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)