Reference

errx(3)

formatted error messages

Part of err(3).

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, 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");

SEE ALSO

exit(3), fmtmsg(3), printf(3), strerror(3), sysexits(3)

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.

History