---
name: "modf"
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/modf"
---

# modf(3)

extract signed integral and fractional values from floating-point number

## NAME

modf, modff, modfl - extract signed integral and fractional values from floating-point number

## LIBRARY

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

## SYNOPSIS

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

**double modf(double** *x***, double \****iptr***);** **float modff(float** *x***, float \****iptr***);** **long double modfl(long double** *x***, long double \****iptr***);**

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

**modff**(), **modfl**():

```
    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
        || /* Since glibc 2.19: */ _DEFAULT_SOURCE
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
```

## DESCRIPTION

These functions break the argument *x* into an integral part and a fractional part, each of which has the same sign as *x*. The integral part is stored in the location pointed to by *iptr*.

## RETURN VALUE

These functions return the fractional part of *x*.

If *x* is a NaN, a NaN is returned, and *\*iptr* is set to a NaN.

If *x* is positive infinity (negative infinity), +0 (-0) is returned, and *\*iptr* is set to positive infinity (negative infinity).

## ERRORS

No errors occur.

## ATTRIBUTES

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

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **modf**(), **modff**(), **modfl**() | Thread safety | MT-Safe |

## STANDARDS

C11, POSIX.1-2008.

## HISTORY

C99, POSIX.1-2001.

The variant returning *double* also conforms to SVr4, 4.3BSD, C89.

## SEE ALSO

[**frexp**(3)](/frexp/3.md), [**ldexp**(3)](/ldexp/3.md)