# Manual Reference Pages  - ERFC (3)

### NAME

erfc, erfcf, erfcl - complementary error function

Synopsis
Description
Return Value
Errors
Notes
Colophon

### 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():

_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
or cc -std=c99

erfcf(), erfcl():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600|| _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
or cc -std=c99

### DESCRIPTION

The erfc() function returns 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.

### CONFORMING TO

C99, POSIX.1-2001. The variant returning double also conforms to SVr4, 4.3BSD.

### NOTES

The erfc() 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).