# erfc - Man Page

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)):

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).

InterfaceAttributeValue
erfc(), erfcf(), erfcl()Thread safetyMT-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).