err(), errx()

Display a formatted error message, and then exit

Synopsis:

#include <err.h>

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

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

Arguments:

eval

The value to use as the exit code of the process.

fmt

NULL, or a printf()-style string used to format the message.

Additional arguments

As required by the format string.

Library:

libc

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

Description:

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.

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 last component of the program name, followed by a colon and a space
• the formatted message, if the fmt argument isn't NULL
• a newline character.

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

Examples:

Display the current errno information string and 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 exit:

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

Classification:

Unix

See also:

printf(), stderr, strerror(), verr(), verrx(), vwarn(), vwarnx(), warn(), warnx()