err(3) - NetBSD Manual Pages

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ERR(3)                  NetBSD Library Functions Manual                 ERR(3)


NAME

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


LIBRARY

     Standard C Library (libc, -lc)


SYNOPSIS

     #include <err.h>

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

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

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

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

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

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

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

     void
     vwarn(const char *fmt, va_list args);

     void
     warnx(const char *fmt, ...);

     void
     vwarnx(const char *fmt, va_list args);

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

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


DESCRIPTION

     The err() and warn() family of functions display a formatted error mes-
     sage on the standard error output.

     In all cases these functions output the last component of the program
     name, a colon character, and a space.  If the fmt argument is not NULL,
     it is used as a printf(3)-like format specification for the error mes-
     sage.

     In the case of the err(), verr(), warn(), and vwarn() functions, an addi-
     tional error message string affiliated with the current value of the
     global variable errno is output next, preceded by a colon character and a
     space if fmt is not NULL.  The errc(), verrc(), warnc(), and vwarnc()
     functions take an additional code argument to be used as the error number
     instead of using the global errno variable.  The errx(), verrx(),
     warnx(), and vwarnx() functions will not output an additional error mes-
     sage string.

     In all cases, the output is terminated by a newline character.

     The err(), verr(), errc(), verrc(), errx(), and verrx() functions do not
     return, but instead cause the program to terminate with the status value
     given by the argument status.  It is often appropriate to use the value
     EXIT_FAILURE, defined in <stdlib.h>, as the status argument given to
     these functions.


EXAMPLES

     Display the current errno information string and terminate with status
     indicating failure:

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

     Display an error message and terminate with status indicating failure:

           if (tm.tm_hour < START_TIME)
                   errx(EXIT_FAILURE, "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)
                   warn("%s", block_device);


SEE ALSO

     exit(3), getprogname(3), printf(3), strerror(3)


HISTORY

     The err() and warn() functions first appeared in 4.4BSD.  The errc() and
     warnc() functions first appeared in FreeBSD 3.0 and NetBSD 7.0.


CAVEATS

     It is important never to pass a string with user-supplied data as a for-
     mat without using `%s'.  An attacker can put format specifiers in the
     string to mangle your stack, leading to a possible security hole.  This
     holds true even if you have built the string ``by hand'' using a function
     like snprintf(), as the resulting string may still contain user-supplied
     conversion specifiers for later interpolation by the err() and warn()
     functions.

     Always be sure to use the proper secure idiom:

           err(1, "%s", string);

NetBSD 10.99                   February 2, 2024                   NetBSD 10.99