# Manual Reference Pages  - FPCLASSIFY (3)

### NAME

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

Synopsis
Description
Notes
Colophon

### 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():

_XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
or cc -std=c99
isnan():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
or cc -std=c99
isinf():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
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.)