xref: /dragonfly/lib/libc/gen/err.3 (revision d4ef6694) 
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28.\"	From: @(#)err.3	8.1 (Berkeley) 6/9/93
29.\" $FreeBSD: src/lib/libc/gen/err.3,v 1.24 2008/10/31 15:14:40 rwatson Exp $
30.\"
31.Dd March 6, 1999
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 ,
143.Fn verrx ,
144.Fn warnx ,
145and
146.Fn vwarnx
147functions do not append an error message.
148.Pp
149The
150.Fn err ,
151.Fn verr ,
152.Fn errc ,
153.Fn verrc ,
154.Fn errx ,
155and
156.Fn verrx
157functions do not return, but exit with the value of the argument
158.Fa eval .
159It is recommended that the standard values defined in
160.Xr sysexits 3
161be used for the value of
162.Fa eval .
163The
164.Fn err_set_exit
165function can be used to specify a function which is called before
166.Xr exit 3
167to perform any necessary cleanup; passing a null function pointer for
168.Va exitf
169resets the hook to do nothing.
170The
171.Fn err_set_file
172function sets the output stream used by the other functions.
173Its
174.Fa vfp
175argument must be either a pointer to an open stream
176(possibly already converted to void *)
177or a null pointer
178(in which case the output stream is set to standard error).
179.Sh EXAMPLES
180Display the current
181.Va errno
182information string and exit:
183.Bd -literal -offset indent
184if ((p = malloc(size)) == NULL)
185	err(EX_OSERR, NULL);
186if ((fd = open(file_name, O_RDONLY, 0)) == -1)
187	err(EX_NOINPUT, "%s", file_name);
188.Ed
189.Pp
190Display an error message and exit:
191.Bd -literal -offset indent
192if (tm.tm_hour < START_TIME)
193	errx(EX_DATAERR, "too early, wait until %s",
194	    start_time_string);
195.Ed
196.Pp
197Warn of an error:
198.Bd -literal -offset indent
199if ((fd = open(raw_device, O_RDONLY, 0)) == -1)
200	warnx("%s: %s: trying the block device",
201	    raw_device, strerror(errno));
202if ((fd = open(block_device, O_RDONLY, 0)) == -1)
203	err(EX_OSFILE, "%s", block_device);
204.Ed
205.Pp
206Warn of an error without using the global variable
207.Va errno :
208.Bd -literal -offset indent
209error = my_function();	/* returns a value from <errno.h> */
210if (error != 0)
211	warnc(error, "my_function");
212.Ed
213.Sh SEE ALSO
214.Xr exit 3 ,
215.Xr fmtmsg 3 ,
216.Xr printf 3 ,
217.Xr strerror 3 ,
218.Xr sysexits 3
219.Sh HISTORY
220The
221.Fn err
222and
223.Fn warn
224functions first appeared in
225.Bx 4.4 .
226The
227.Fn err_set_exit
228and
229.Fn err_set_file
230functions first appeared in
231.Fx 2.1 .
232The
233.Fn errc
234and
235.Fn warnc
236functions first appeared in
237.Fx 3.0 .
238