---
name: "err"
section: "3"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/err"
---

# err(3)

formatted error messages

## NAME

**err**, **verr**, **errc**, **verrc**, **errx**, **verrx**, **warn**, **vwarn**, **warnc**, **vwarnc**, **warnx**, **vwarnx**, **err\_set\_exit**, **err\_set\_file** – formatted error messages

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

**#include \<err.h\>**

*void*\

**err**(*int eval*, *const char \*fmt*, *...*);

*void*\

**err\_set\_exit**(*void (\*exitf)(int)*);

*void*\

**err\_set\_file**(*void \*vfp*);

*void*\

**errc**(*int eval*, *int code*, *const char \*fmt*, *...*);

*void*\

**errx**(*int eval*, *const char \*fmt*, *...*);

*void*\

**warn**(*const char \*fmt*, *...*);

*void*\

**warnc**(*int code*, *const char \*fmt*, *...*);

*void*\

**warnx**(*const char \*fmt*, *...*);

**#include \<stdarg.h\>**

*void*\

**verr**(*int eval*, *const char \*fmt*, *va\_list args*);

*void*\

**verrc**(*int eval*, *int code*, *const char \*fmt*, *va\_list args*);

*void*\

**verrx**(*int eval*, *const char \*fmt*, *va\_list args*);

*void*\

**vwarn**(*const char \*fmt*, *va\_list args*);

*void*\

**vwarnc**(*int code*, *const char \*fmt*, *va\_list args*);

*void*\

**vwarnx**(*const char \*fmt*, *va\_list args*);

## DESCRIPTION

The **err**() and **warn**() family of functions display a formatted error message on the standard error output, or on another file specified using the **err\_set\_file**() function. In all cases, the last component of the program name, a colon character, and a space are output. If the *fmt* argument is not NULL, the[printf(3)](/printf/3.md) -like formatted error message is output. The output is terminated by a newline character.

The **err**(), **errc**(), **verr**(), **verrc**(), **warn**(), **warnc**(), **vwarn**(), and **vwarnc**() functions append an error message obtained from [strerror(3)](/strerror/3.md) based on a supplied error code value or the global variable *errno*, preceded by another colon and space unless the *fmt* argument is NULL.

If the kernel returned an extended error string in addition to the *errno* code, the **err**() function prints the string with interpolated values for parameters, as provided to the corresponding invocation of EXTERROR(9). If the extended error string was not provided, but extended error information was, or even if string was provided and the EXTERROR\_VERBOSE environment variable is present, an additional report is printed. The report includes at least the category of the error, the name of the source file (if known by the used version of libc), the source line number, and parameters. If the EXTERROR\_VERBOSE environment variable is present and set to "brief", the report adds only the name of the source file (if known by the used version of libc) and the source line number. The format of the printed string is not contractual and might be changed.

In the case of the **errc**(), **verrc**(), **warnc**(), and **vwarnc**() functions, the *code* argument is used to look up the error message.

The **err**(), **verr**(), **warn**(), and **vwarn**() functions use the global variable *errno* to look up the error message.

The **errx**() and **warnx**() functions do not append an error message.

The **err**(), **verr**(), **errc**(), **verrc**(), **errx**(), and **verrx**() functions do not return, but exit with the value of the argument *eval*. It is recommended that the standard values defined in [sysexits(3)](/sysexits/3.md) be used for the value of *eval*. The **err\_set\_exit**() function can be used to specify a function which is called before [exit(3)](/exit/3.md) to perform any necessary cleanup; passing a null function pointer for *exitf* resets the hook to do nothing. The **err\_set\_file**() function sets the output stream used by the other functions. Its *vfp* argument must be either a pointer to an open stream (possibly already converted to void \*) or a null pointer (in which case the output stream is set to standard error).

## EXAMPLES

Display the current errno information string and exit:

```
if ((p = malloc(size)) == NULL)
	err(EX_OSERR, NULL);
if ((fd = open(file_name, O_RDONLY, 0)) == -1)
	err(EX_NOINPUT, "%s", file_name);
```

Display an error message and exit:

```
if (tm.tm_hour < START_TIME)
	errx(EX_DATAERR, "too early, wait until %s",
	    start_time_string);
```

Warn of an error:

```
if ((fd = open(raw_device, O_RDONLY, 0)) == -1)
	warnx("%s: %s: trying the block device",
	    raw_device, strerror(errno));
if ((fd = open(block_device, O_RDONLY, 0)) == -1)
	err(EX_OSFILE, "%s", block_device);
```

Warn of an error without using the global variable *errno*:

```
error = my_function();	/* returns a value from <errno.h> */
if (error != 0)
	warnc(error, "my_function");
```

## SEE ALSO

[exit(3)](/exit/3.md), [fmtmsg(3)](/fmtmsg/3.md), [printf(3)](/printf/3.md), [strerror(3)](/strerror/3.md), [sysexits(3)](/sysexits/3.md)

## STANDARDS

The **err**() and **warn**() families of functions are BSD extensions. As such they should not be used in truly portable code. Use **strerror**() or similar functions instead.

## HISTORY

The **err**() and **warn**() functions first appeared in 4.4BSD. The **err\_set\_exit**() and **err\_set\_file**() functions first appeared in FreeBSD 2.1. The **errc**() and **warnc**() functions first appeared in FreeBSD 3.0.