# erfc - Man Page

complementary error function

## Synopsis

#include <math.h> double erfc(doublex); float erfcf(floatx); long double erfcl(long doublex);

`Link with `

*-lm*.

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

**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) 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).

Interface | Attribute | Value |
---|---|---|

erfc(), erfcf(), erfcl() | Thread safety | MT-Safe |

## Conforming to

C99, POSIX.1-2001, POSIX.1-2008.

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

## Colophon

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## Referenced By

The man pages erfcf(3) and erfcl(3) are aliases of erfc(3).