# erfc(3) — Linux manual page

```erfc(3)                 Library Functions Manual                 erfc(3)
```

## NAME         top

```       erfc, erfcf, erfcl - complementary error function
```

## LIBRARY         top

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

## SYNOPSIS         top

```       #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         top

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

## RETURN VALUE         top

```       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         top

```       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         top

```       For an explanation of the terms used in this section, see
attributes(7).
┌─────────────────────────────────────┬───────────────┬─────────┐
│ Interface                           │ Attribute     │ Value   │
├─────────────────────────────────────┼───────────────┼─────────┤
│ erfc(), erfcf(), erfcl()            │ Thread safety │ MT-Safe │
└─────────────────────────────────────┴───────────────┴─────────┘
```

## STANDARDS         top

```       C11, POSIX.1-2008.
```

## HISTORY         top

```       C99, POSIX.1-2001.

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

## NOTES         top

```       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).
```

```       cerf(3), erf(3), exp(3)