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Manual Pages  — ERR


err, verr, errc, verrc, errx, verrx, warn, vwarn, warnc, vwarnc, warnx, vwarnx, err_set_exit, err_set_file – formatted error messages



Standard C Library (libc, -lc)


#include <err.h>

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

err_set_exit(void (*exitf)(int));

err_set_file(void *vfp);

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

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

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

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

warnx(const char *fmt, ...);
#include <stdarg.h>

verr(int eval, const char *fmt, va_list args);

verrc(int eval, int code, const char *fmt, va_list args);

verrx(int eval, const char *fmt, va_list args);

vwarn(const char *fmt, va_list args);

vwarnc(int code, const char *fmt, va_list args);

vwarnx(const char *fmt, va_list args);


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) -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.

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).


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",

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");


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


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.


The err() and warn() functions first appeared in BSD 4.4 . 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 .

ERR (3) March 29, 2012

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