fpclassify - Online Linux Manual PageSection : 3
Updated : 2023-02-05
Source : Linux man-pages 6.03

NAMEfpclassify, isfinite, isnormal, isnan, isinf − floating-point classification macros

LIBRARYMath 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 >= 200112Lisnan(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCEisinf(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

DESCRIPTIONFloating 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.

ATTRIBUTESFor an explanation of the terms used in this section, see attributes(7). InterfaceAttributeValue fpclassify(), isfinite(), isnormal(), isnan(), isinf() Thread safetyMT-Safe

STANDARDSPOSIX.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.

NOTESIn 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 ALSOfinite(3), INFINITY(3), isgreater(3), signbit(3)
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