Manpages - fpclassify.3

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

  #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

*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

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.

For an explanation of the terms used in this section, see *attributes*(7).

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.

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.)

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

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