xref: /dragonfly/lib/libc/gen/err.3 (revision 9f3fc534) 
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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.\" $DragonFly: src/lib/libc/gen/err.3,v 1.4 2008/10/06 21:21:30 swildner Exp $
31.\"
32.Dd March 6, 1999
33.Dt ERR 3
34.Os
35.Sh NAME
36.Nm err ,
37.Nm verr ,
38.Nm errc ,
39.Nm verrc ,
40.Nm errx ,
41.Nm verrx ,
42.Nm warn ,
43.Nm vwarn ,
44.Nm warnc ,
45.Nm vwarnc ,
46.Nm warnx ,
47.Nm vwarnx ,
48.Nm err_set_exit ,
49.Nm err_set_file
50.Nd formatted error messages
51.Sh LIBRARY
52.Lb libc
53.Sh SYNOPSIS
54.In err.h
55.Ft void
56.Fn err "int eval" "const char *fmt" "..."
57.Ft void
58.Fn err_set_exit "void (*exitf)(int)"
59.Ft void
60.Fn err_set_file "void *vfp"
61.Ft void
62.Fn errc "int eval" "int code" "const char *fmt" "..."
63.Ft void
64.Fn errx "int eval" "const char *fmt" "..."
65.Ft void
66.Fn warn "const char *fmt" "..."
67.Ft void
68.Fn warnc "int code" "const char *fmt" "..."
69.Ft void
70.Fn warnx "const char *fmt" "..."
71.In stdarg.h
72.Ft void
73.Fn verr "int eval" "const char *fmt" "va_list args"
74.Ft void
75.Fn verrc "int eval" "int code" "const char *fmt" "va_list args"
76.Ft void
77.Fn verrx "int eval" "const char *fmt" "va_list args"
78.Ft void
79.Fn vwarn "const char *fmt" "va_list args"
80.Ft void
81.Fn vwarnc "int code" "const char *fmt" "va_list args"
82.Ft void
83.Fn vwarnx "const char *fmt" "va_list args"
84.Sh DESCRIPTION
85The
86.Fn err
87and
88.Fn warn
89family of functions display a formatted error message on the standard
90error output, or on another file specified using the
91.Fn err_set_file
92function.
93In all cases, the last component of the program name, a colon character,
94and a space are output.
95If the
96.Fa fmt
97argument is not NULL, the
98.Xr printf 3 Ns
99-like formatted error message is output.
100The output is terminated by a newline character.
101.Pp
102The
103.Fn err ,
104.Fn errc ,
105.Fn verr ,
106.Fn verrc ,
107.Fn warn ,
108.Fn warnc ,
109.Fn vwarn ,
110and
111.Fn vwarnc
112functions append an error message obtained from
113.Xr strerror 3
114based on a supplied error code value or the global variable
115.Va errno ,
116preceded by another colon and space unless the
117.Fa fmt
118argument is
119.Dv NULL .
120.Pp
121In the case of the
122.Fn errc ,
123.Fn verrc ,
124.Fn warnc ,
125and
126.Fn vwarnc
127functions,
128the
129.Fa code
130argument is used to look up the error message.
131.Pp
132The
133.Fn err ,
134.Fn verr ,
135.Fn warn ,
136and
137.Fn vwarn
138functions use the global variable
139.Va errno
140to look up the error message.
141.Pp
142The
143.Fn errx
144and
145.Fn warnx
146functions do not append an error message.
147.Pp
148The
149.Fn err ,
150.Fn verr ,
151.Fn errc ,
152.Fn verrc ,
153.Fn errx ,
154and
155.Fn verrx
156functions do not return, but exit with the value of the argument
157.Fa eval .
158It is recommended that the standard values defined in
159.Xr sysexits 3
160be used for the value of
161.Fa eval .
162The
163.Fn err_set_exit
164function can be used to specify a function which is called before
165.Xr exit 3
166to perform any necessary cleanup; passing a null function pointer for
167.Va exitf
168resets the hook to do nothing.
169The
170.Fn err_set_file
171function sets the output stream used by the other functions.
172Its
173.Fa vfp
174argument must be either a pointer to an open stream
175(possibly already converted to void *)
176or a null pointer
177(in which case the output stream is set to standard error).
178.Sh EXAMPLES
179Display the current
180.Va errno
181information string and exit:
182.Bd -literal -offset indent
183if ((p = malloc(size)) == NULL)
184	err(EX_OSERR, NULL);
185if ((fd = open(file_name, O_RDONLY, 0)) == -1)
186	err(EX_NOINPUT, "%s", file_name);
187.Ed
188.Pp
189Display an error message and exit:
190.Bd -literal -offset indent
191if (tm.tm_hour < START_TIME)
192	errx(EX_DATAERR, "too early, wait until %s",
193	    start_time_string);
194.Ed
195.Pp
196Warn of an error:
197.Bd -literal -offset indent
198if ((fd = open(raw_device, O_RDONLY, 0)) == -1)
199	warnx("%s: %s: trying the block device",
200	    raw_device, strerror(errno));
201if ((fd = open(block_device, O_RDONLY, 0)) == -1)
202	err(EX_OSFILE, "%s", block_device);
203.Ed
204.Pp
205Warn of an error without using the global variable
206.Va errno :
207.Bd -literal -offset indent
208error = my_function();	/* returns a value from <errno.h> */
209if (error != 0)
210	warnc(error, "my_function");
211.Ed
212.Sh SEE ALSO
213.Xr exit 3 ,
214.Xr fmtmsg 3 ,
215.Xr printf 3 ,
216.Xr strerror 3 ,
217.Xr sysexits 3
218.Sh HISTORY
219The
220.Fn err
221and
222.Fn warn
223functions first appeared in
224.Bx 4.4 .
225The
226.Fn err_set_exit
227and
228.Fn err_set_file
229functions first appeared in
230.Fx 2.1 .
231The
232.Fn errc
233and
234.Fn warnc
235functions first appeared in
236.Fx 3.0 .
237