1ERRC(3bsd)                           LOCAL                          ERRC(3bsd)
2

NAME

4     errc, verrc, warnc, vwarnc — formatted error messages
5

LIBRARY

7     Utility functions from BSD systems (libbsd, -lbsd)
8

SYNOPSIS

10     #include <err.h>
11     (See libbsd(7) for include usage.)
12
13     void
14     errc(int status, int code, const char *fmt, ...);
15
16     void
17     verrc(int status, int code, const char *fmt, va_list args);
18
19     void
20     warnc(int code, const char *fmt, ...);
21
22     void
23     vwarnc(int code, const char *fmt, va_list args);
24

DESCRIPTION

26     The err() and warn() family of functions display a formatted error mes‐
27     sage on the standard error output.  In all cases, the last component of
28     the program name, followed by a colon (‘:’) character and a space, are
29     output.  The text that follows depends on the function being called.  The
30     fmt specification (and associated arguments) may be any format allowed by
31     printf(3) or NULL.  If the fmt argument is not NULL, the formatted error
32     message is output.
33
34     The functions all output an error message string affiliated with an error
35     value (see strerror(3)), preceded by a colon character and a space if fmt
36     is not NULL.  That is, the output is as follows:
37
38           progname: fmt: error message string
39
40     if fmt is not NULL, or:
41
42           progname: error message string
43
44     if it is.
45
46     The argument code is used as the error value instead of the current value
47     of the global variable errno.
48
49     In all cases, the output is followed by a newline character.
50
51     The errc(), and verrc() functions do not return, but exit with the value
52     of the argument status.
53

EXAMPLES

55     Display the current errno information string and exit:
56
57           if ((p = malloc(size)) == NULL)
58                   err(1, NULL);
59           if ((fd = open(file_name, O_RDONLY, 0)) == -1)
60                   err(1, "%s", file_name);
61
62     Display an error message and exit:
63
64           if (tm.tm_hour < START_TIME)
65                   errx(1, "too early, wait until %s", start_time_string);
66
67     Warn of an error:
68
69           if ((fd = open(raw_device, O_RDONLY, 0)) == -1)
70                   warnx("%s: %s: trying the block device",
71                       raw_device, strerror(errno));
72           if ((fd = open(block_device, O_RDONLY, 0)) == -1)
73                   err(1, "%s", block_device);
74

SEE ALSO

76     err(3) exit(3), perror(3), printf(3), strerror(3)
77

HISTORY

79     The functions errc(), verrc(), warnc(), and vwarnc() first appeared in
80     FreeBSD 3.0, NetBSD 7.0 and OpenBSD 5.6.
81

CAVEATS

83     It is important never to pass a string with user-supplied data as a for‐
84     mat without using ‘%s’.  An attacker can put format specifiers in the
85     string to mangle the stack, leading to a possible security hole.  This
86     holds true even if the string has been built “by hand” using a function
87     like snprintf(), as the resulting string may still contain user-supplied
88     conversion specifiers for later interpolation by the err() and warn()
89     family of functions.
90
91     Always be sure to use the proper secure idiom:
92
93           errc(1, 0, "%s", string);
94
95BSD                              June 20, 2019                             BSD
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