carta
err_set_file(3)

err_set_file3

Formatted error messages

Part of err(3).

Usage

void

void

void

void

void

void

void

void

void

void

void

void

void

void

Library

Standard C Library (libc, -lc)

Overview

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, theprintf(3) -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) 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) 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) 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");

History

  • FreeBSD 16.0-CURRENT (2026-10-27) to FreeBSD 15.1-RELEASE: the text shown here
  • FreeBSD 15.0-RELEASE
  • FreeBSD 14.5-RELEASE to FreeBSD 13.3-RELEASE
  • FreeBSD 13.2-RELEASE to FreeBSD 13.0-RELEASE
  • FreeBSD 12.4-RELEASE
  • FreeBSD 12.3-RELEASE
  • FreeBSD 12.2-RELEASE
  • FreeBSD 12.1-RELEASE
  • FreeBSD 12.0-RELEASE
  • FreeBSD 11.4-RELEASE
  • FreeBSD 11.3-RELEASE
  • FreeBSD 11.2-RELEASE
  • FreeBSD 11.1-RELEASE
  • FreeBSD 11.0-RELEASE
  • FreeBSD 10.4-RELEASE
  • FreeBSD 10.3-RELEASE
  • FreeBSD 10.2-RELEASE
  • FreeBSD 10.1-RELEASE
  • FreeBSD 10.0-RELEASE
  • FreeBSD 9.3-RELEASE
  • FreeBSD 9.2-RELEASE
  • FreeBSD 9.1-RELEASE
  • FreeBSD 9.0-RELEASE
  • FreeBSD 8.4-RELEASE
  • FreeBSD 8.3-RELEASE
  • FreeBSD 8.2-RELEASE
  • FreeBSD 8.1-RELEASE
  • FreeBSD 8.0-RELEASE
  • FreeBSD 7.4-RELEASE
  • FreeBSD 7.3-RELEASE
  • FreeBSD 7.2-RELEASE
  • FreeBSD 7.1-RELEASE
  • FreeBSD 7.0-RELEASE
  • FreeBSD 6.4-RELEASE
  • FreeBSD 6.3-RELEASE to FreeBSD 6.0-RELEASE
  • FreeBSD 5.5-RELEASE to FreeBSD 5.0-RELEASE
  • FreeBSD 4.11-RELEASE to FreeBSD 4.5-RELEASE
  • FreeBSD 4.4-RELEASE
  • FreeBSD 4.3-RELEASE
  • FreeBSD 4.2-RELEASE to FreeBSD 4.1-RELEASE
  • FreeBSD 4.0-RELEASE
  • FreeBSD 3.5.1-RELEASE to FreeBSD 3.5-RELEASE
  • FreeBSD 3.4-RELEASE to FreeBSD 3.3-RELEASE
  • FreeBSD 3.2-RELEASE to FreeBSD 3.0-RELEASE
  • FreeBSD 2.2.9-RELEASE
  • FreeBSD 2.2.8-RELEASE to FreeBSD 2.2.7-RELEASE
  • FreeBSD 2.2.6-RELEASE to FreeBSD 2.2.2-RELEASE

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.

From base 16.0-CURRENT-20261027-61c70dc16a79 in FreeBSD 16.0-CURRENT (2026-10-27). Parsed by carta from the page's mdoc source.