err(), errx()

Synopsis:

#include <err.h>

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

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

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

The err() and warn() family of functions display a formatted error message on stderr:

The functions without an x in their names display the string associated with the current value of errno.
Those with a v are “varargs” functions.
Those with err exit instead of returning.

Function	`errno` string?	Varargs?	Exits?
err()	Yes	No	Yes
errx()	No	No	Yes
verr()	Yes	Yes	Yes
verrx()	No	Yes	Yes
vwarn()	Yes	Yes	No
vwarnx()	No	Yes	No
warn()	Yes	No	No
warnx()	No	No	No

The err() function produces a message that consists of:

the last component of the program name, followed by a colon and a space
the formatted message, followed by a colon and a space, if the fmt argument isn't NULL
the string associated with the current value of errno
a newline character.

The errx() function produces a similar message, except that it doesn't include the string associated with errno. The message consists of:

The err() and errx() functions don't return, but exit with the value of the argument eval.

Display the current errno information string, and then exit:

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

Display an error message, and then exit:

if (tm.tm_hour < START_TIME)
    errx(1, "too early, wait until %s", start_time_string);