---
name: "erfc"
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/erfc"
---

# erfc(3)

complementary error function

## NAME

erfc, erfcf, erfcl - complementary error function

## LIBRARY

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

## SYNOPSIS

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

**double erfc(double** *x***);** **float erfcf(float** *x***);** **long double erfcl(long double** *x***);**

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

**erfc**():

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

**erfcf**(), **erfcl**():

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

## DESCRIPTION

These functions return the complementary error function of *x*, that is, 1.0 - erf(x).

## RETURN VALUE

On success, these functions return the complementary error function of *x*, a value in the range \[0,2\].

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

If *x* is +0 or -0, 1 is returned.

If *x* is positive infinity, +0 is returned.

If *x* is negative infinity, +2 is returned.

If the function result underflows and produces an unrepresentable value, the return value is 0.0.

If the function result underflows but produces a representable (i.e., subnormal) value, that value is returned, and a range error occurs.

## 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 underflow (result is subnormal)

  An underflow floating-point exception (**FE\_UNDERFLOW**) is raised.

These functions do not set *errno*.

## ATTRIBUTES

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

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **erfc**(), **erfcf**(), **erfcl**() | Thread safety | MT-Safe |

## STANDARDS

C11, POSIX.1-2008.

## HISTORY

C99, POSIX.1-2001.

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

## NOTES

The **erfc**(), **erfcf**(), and **erfcl**() functions are provided to avoid the loss accuracy that would occur for the calculation 1-erf(x) for large values of *x* (for which the value of erf(x) approaches 1).

## SEE ALSO

[**cerf**(3)](/cerf/3.md), [**erf**(3)](/erf/3.md), [**exp**(3)](/exp/3.md)