---
name: "finite"
section: "3"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/finite"
---

# finite(3)

BSD floating-point classification functions

## NAME

finite, finitef, finitel, isinf, isinff, isinfl, isnan, isnanf, isnanl - BSD floating-point classification functions

## LIBRARY

Math library (*libm*, *-lm*)

## SYNOPSIS

```
#include <math.h>
```

**int finite(double** *x***);** **int finitef(float** *x***);** **int finitel(long double** *x***);**

**int isinf(double** *x***);** **int isinff(float** *x***);** **int isinfl(long double** *x***);**

**int isnan(double** *x***);** **int isnanf(float** *x***);** **int isnanl(long double** *x***);**

Feature Test Macro Requirements for glibc (see [**feature\_test\_macros**(7)](/feature_test_macros/7.md)):

**finite**(), **finitef**(), **finitel**():

```
    /* glibc >= 2.19: */ _DEFAULT_SOURCE
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
```

**isinf**():\
     \_XOPEN\_SOURCE \>= 600 \|\| \_ISOC99\_SOURCE\
         \|\| /\* glibc \>= 2.19: \*/ \_DEFAULT\_SOURCE\
         \|\| /\* glibc \<= 2.19: \*/ \_BSD\_SOURCE \|\| \_SVID\_SOURCE

**isinff**(), **isinfl**():

```
    /* glibc >= 2.19: */ _DEFAULT_SOURCE
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
```

**isnan**():

```
    _XOPEN_SOURCE || _ISOC99_SOURCE
        || /* glibc >= 2.19: */ _DEFAULT_SOURCE
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
```

**isnanf**(), **isnanl**():

```
    _XOPEN_SOURCE >= 600
        || /* glibc >= 2.19: */ _DEFAULT_SOURCE
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
```

## DESCRIPTION

The **finite**(), **finitef**(), and **finitel**() functions return a nonzero value if *x* is neither infinite nor a "not-a-number" (NaN) value, and 0 otherwise.

The **isnan**(), **isnanf**(), and **isnanl**() functions return a nonzero value if *x* is a NaN value, and 0 otherwise.

The **isinf**(), **isinff**(), and **isinfl**() functions return 1 if *x* is positive infinity, -1 if *x* is negative infinity, and 0 otherwise.

## ATTRIBUTES

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

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **finite**(), **finitef**(), **finitel**(), **isinf**(), **isinff**(), **isinfl**(), **isnan**(), **isnanf**(), **isnanl**() | Thread safety | MT-Safe |

## NOTES

Note that these functions are obsolete. C99 defines macros **isfinite**(), **isinf**(), and **isnan**() (for all types) replacing them. Further note that the C99 **isinf**() has weaker guarantees on the return value. See [**fpclassify**(3)](/fpclassify/3.md).

## SEE ALSO

[**fpclassify**(3)](/fpclassify/3.md)