xref: /freebsd/lib/libc/gen/err.3 (revision 81ad6265) 
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28.\"	From: @(#)err.3	8.1 (Berkeley) 6/9/93
29.\" $FreeBSD$
30.\"
31.Dd March 29, 2012
32.Dt ERR 3
33.Os
34.Sh NAME
35.Nm err ,
36.Nm verr ,
37.Nm errc ,
38.Nm verrc ,
39.Nm errx ,
40.Nm verrx ,
41.Nm warn ,
42.Nm vwarn ,
43.Nm warnc ,
44.Nm vwarnc ,
45.Nm warnx ,
46.Nm vwarnx ,
47.Nm err_set_exit ,
48.Nm err_set_file
49.Nd formatted error messages
50.Sh LIBRARY
51.Lb libc
52.Sh SYNOPSIS
53.In err.h
54.Ft void
55.Fn err "int eval" "const char *fmt" "..."
56.Ft void
57.Fn err_set_exit "void (*exitf)(int)"
58.Ft void
59.Fn err_set_file "void *vfp"
60.Ft void
61.Fn errc "int eval" "int code" "const char *fmt" "..."
62.Ft void
63.Fn errx "int eval" "const char *fmt" "..."
64.Ft void
65.Fn warn "const char *fmt" "..."
66.Ft void
67.Fn warnc "int code" "const char *fmt" "..."
68.Ft void
69.Fn warnx "const char *fmt" "..."
70.In stdarg.h
71.Ft void
72.Fn verr "int eval" "const char *fmt" "va_list args"
73.Ft void
74.Fn verrc "int eval" "int code" "const char *fmt" "va_list args"
75.Ft void
76.Fn verrx "int eval" "const char *fmt" "va_list args"
77.Ft void
78.Fn vwarn "const char *fmt" "va_list args"
79.Ft void
80.Fn vwarnc "int code" "const char *fmt" "va_list args"
81.Ft void
82.Fn vwarnx "const char *fmt" "va_list args"
83.Sh DESCRIPTION
84The
85.Fn err
86and
87.Fn warn
88family of functions display a formatted error message on the standard
89error output, or on another file specified using the
90.Fn err_set_file
91function.
92In all cases, the last component of the program name, a colon character,
93and a space are output.
94If the
95.Fa fmt
96argument is not NULL, the
97.Xr printf 3 Ns
98-like formatted error message is output.
99The output is terminated by a newline character.
100.Pp
101The
102.Fn err ,
103.Fn errc ,
104.Fn verr ,
105.Fn verrc ,
106.Fn warn ,
107.Fn warnc ,
108.Fn vwarn ,
109and
110.Fn vwarnc
111functions append an error message obtained from
112.Xr strerror 3
113based on a supplied error code value or the global variable
114.Va errno ,
115preceded by another colon and space unless the
116.Fa fmt
117argument is
118.Dv NULL .
119.Pp
120In the case of the
121.Fn errc ,
122.Fn verrc ,
123.Fn warnc ,
124and
125.Fn vwarnc
126functions,
127the
128.Fa code
129argument is used to look up the error message.
130.Pp
131The
132.Fn err ,
133.Fn verr ,
134.Fn warn ,
135and
136.Fn vwarn
137functions use the global variable
138.Va errno
139to look up the error message.
140.Pp
141The
142.Fn errx
143and
144.Fn warnx
145functions do not append an error message.
146.Pp
147The
148.Fn err ,
149.Fn verr ,
150.Fn errc ,
151.Fn verrc ,
152.Fn errx ,
153and
154.Fn verrx
155functions do not return, but exit with the value of the argument
156.Fa eval .
157It is recommended that the standard values defined in
158.Xr sysexits 3
159be used for the value of
160.Fa eval .
161The
162.Fn err_set_exit
163function can be used to specify a function which is called before
164.Xr exit 3
165to perform any necessary cleanup; passing a null function pointer for
166.Va exitf
167resets the hook to do nothing.
168The
169.Fn err_set_file
170function sets the output stream used by the other functions.
171Its
172.Fa vfp
173argument must be either a pointer to an open stream
174(possibly already converted to void *)
175or a null pointer
176(in which case the output stream is set to standard error).
177.Sh EXAMPLES
178Display the current errno information string and exit:
179.Bd -literal -offset indent
180if ((p = malloc(size)) == NULL)
181	err(EX_OSERR, NULL);
182if ((fd = open(file_name, O_RDONLY, 0)) == -1)
183	err(EX_NOINPUT, "%s", file_name);
184.Ed
185.Pp
186Display an error message and exit:
187.Bd -literal -offset indent
188if (tm.tm_hour < START_TIME)
189	errx(EX_DATAERR, "too early, wait until %s",
190	    start_time_string);
191.Ed
192.Pp
193Warn of an error:
194.Bd -literal -offset indent
195if ((fd = open(raw_device, O_RDONLY, 0)) == -1)
196	warnx("%s: %s: trying the block device",
197	    raw_device, strerror(errno));
198if ((fd = open(block_device, O_RDONLY, 0)) == -1)
199	err(EX_OSFILE, "%s", block_device);
200.Ed
201.Pp
202Warn of an error without using the global variable
203.Va errno :
204.Bd -literal -offset indent
205error = my_function();	/* returns a value from <errno.h> */
206if (error != 0)
207	warnc(error, "my_function");
208.Ed
209.Sh SEE ALSO
210.Xr exit 3 ,
211.Xr fmtmsg 3 ,
212.Xr printf 3 ,
213.Xr strerror 3 ,
214.Xr sysexits 3
215.Sh STANDARDS
216The
217.Fn err
218and
219.Fn warn
220families of functions are
221.Bx
222extensions.
223As such they should not be used in truly portable code.
224Use
225.Fn strerror
226or similar functions instead.
227.Sh HISTORY
228The
229.Fn err
230and
231.Fn warn
232functions first appeared in
233.Bx 4.4 .
234The
235.Fn err_set_exit
236and
237.Fn err_set_file
238functions first appeared in
239.Fx 2.1 .
240The
241.Fn errc
242and
243.Fn warnc
244functions first appeared in
245.Fx 3.0 .
246