---
name: "fdim"
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/fdim"
---

# fdim(3)

positive difference

## NAME

fdim, fdimf, fdiml - positive difference

## LIBRARY

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

## SYNOPSIS

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

**double fdim(double** *x***, double** *y***);** **float fdimf(float** *x***, float** *y***);** **long double fdiml(long double** *x***, long double** *y***);**

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

**fdimf**(), **fdiml**():

```
    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
```

## DESCRIPTION

These functions return the positive difference, *max(x-y,0)*, between their arguments.

## RETURN VALUE

On success, these functions return the positive difference.

If *x* or *y* is a NaN, a NaN is returned.

If the result overflows, a range error occurs, and the functions return **HUGE\_VAL**, **HUGE\_VALF**, or **HUGE\_VALL**, respectively.

## ERRORS

See [**math\_error**(7)](/math_error/7.md) for information on how to determine whether an error has occurred when calling these functions.

The following errors can occur:

- Range error: result overflow

  *errno* is set to **ERANGE**. An overflow floating-point exception (**FE\_OVERFLOW**) is raised.

## ATTRIBUTES

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

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **fdim**(), **fdimf**(), **fdiml**() | Thread safety | MT-Safe |

## STANDARDS

C11, POSIX.1-2008.

## HISTORY

glibc 2.1. C99, POSIX.1-2001.

## BUGS

Before glibc 2.24 on certain architectures (e.g., x86, but not x86\_64) these functions did not set *errno*.

## SEE ALSO

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