# Man Page

### Manual Section... (3) - page: isinf

## NAME

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

#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**():
_XOPEN_SOURCE >= 600 || _ISOC99_SOURCE; or
*cc -std=c99*

**isnan**():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE || _ISOC99_SOURCE; or
*cc -std=c99*

**isinf**():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE; or
*cc -std=c99*

## 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.

## CONFORMING TO

C99, POSIX.1.
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)

## COLOPHON

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## Index

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Time: 15:27:06 GMT, June 11, 2010