fpclassify

Section: C Library Functions (3)
Updated: 2023-02-05
Index Return to Main Contents
 

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).
InterfaceAttributeValue
fpclassify(), isfinite(), isnormal(), isnan(), isinf() Thread safetyMT-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)

 

Index

NAME
LIBRARY
SYNOPSIS
DESCRIPTION
ATTRIBUTES
STANDARDS
NOTES
SEE ALSO
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Time: 16:23:29 GMT, April 19, 2024