ERR(3) Library Functions Manual ERR(3)

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

Standard C Library (libc, -lc)

#include <err.h>

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

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

void
err_set_exit_b(void (^exitb)(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);

The () and () 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 (), 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 (), (), (), and () functions, the code argument is used to look up the error message.

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

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

The (), (), errc(), verrc(), errx(), and () 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 () 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 () function is like err_set_exit() except it takes a block pointer instead of a function pointer.

Note: The () function (defined in <Blocks.h>) is used by err_set_exit_b() to make a copy of the block, especially for the case when a stack-based block might go out of scope when the subroutine returns.

The () 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",
	    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");

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

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. The err_set_exit_b() function first appeared in Mac OS X 10.6.

May 20, 2008 macOS 15.2