xref: /dragonfly/lib/libc/gen/err.3 (revision 333227be) 
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32.\"	From: @(#)err.3	8.1 (Berkeley) 6/9/93
33.\" $FreeBSD: src/lib/libc/gen/err.3,v 1.11.2.6 2001/12/14 18:33:51 ru Exp $
34.\" $DragonFly: src/lib/libc/gen/err.3,v 1.2 2003/06/17 04:26:42 dillon Exp $
35.\"
36.Dd March 6, 1999
37.Dt ERR 3
38.Os
39.Sh NAME
40.Nm err ,
41.Nm verr ,
42.Nm errc ,
43.Nm verrc ,
44.Nm errx ,
45.Nm verrx ,
46.Nm warn ,
47.Nm vwarn ,
48.Nm warnc ,
49.Nm vwarnc ,
50.Nm warnx ,
51.Nm vwarnx ,
52.Nm err_set_exit ,
53.Nm err_set_file
54.Nd formatted error messages
55.Sh LIBRARY
56.Lb libc
57.Sh SYNOPSIS
58.In err.h
59.Ft void
60.Fn err "int eval" "const char *fmt" "..."
61.Ft void
62.Fn err_set_exit "void (*exitf)(int)"
63.Ft void
64.Fn err_set_file "void *vfp"
65.Ft void
66.Fn errc "int eval" "int code" "const char *fmt" "..."
67.Ft void
68.Fn errx "int eval" "const char *fmt" "..."
69.Ft void
70.Fn warn "const char *fmt" "..."
71.Ft void
72.Fn warnc "int code" "const char *fmt" "..."
73.Ft void
74.Fn warnx "const char *fmt" "..."
75.In stdarg.h
76.Ft void
77.Fn verr "int eval" "const char *fmt" "va_list args"
78.Ft void
79.Fn verrc "int eval" "int code" "const char *fmt" "va_list args"
80.Ft void
81.Fn verrx "int eval" "const char *fmt" "va_list args"
82.Ft void
83.Fn vwarn "const char *fmt" "va_list args"
84.Ft void
85.Fn vwarnc "int code" "const char *fmt" "va_list args"
86.Ft void
87.Fn vwarnx "const char *fmt" "va_list args"
88.Sh DESCRIPTION
89The
90.Fn err
91and
92.Fn warn
93family of functions display a formatted error message on the standard
94error output, or on another file specified using the
95.Fn err_set_file
96function.
97In all cases, the last component of the program name, a colon character,
98and a space are output.
99If the
100.Fa fmt
101argument is not NULL, the
102.Xr printf 3
103-like formatted error message is output.
104The output is terminated by a newline character.
105.Pp
106The
107.Fn err ,
108.Fn errc ,
109.Fn verr ,
110.Fn verrc ,
111.Fn warn ,
112.Fn warnc ,
113.Fn vwarn ,
114and
115.Fn vwarnc
116functions append an error message obtained from
117.Xr strerror 3
118based on a code or the global variable
119.Va errno ,
120preceded by another colon and space unless the
121.Fa fmt
122argument is
123.Dv NULL .
124.Pp
125In the case of the
126.Fn errc ,
127.Fn verrc ,
128.Fn warnc ,
129and
130.Fn vwarnc
131functions,
132the
133.Fa code
134argument is used to look up the error message.
135.Pp
136The
137.Fn err ,
138.Fn verr ,
139.Fn warn ,
140and
141.Fn vwarn
142functions use the global variable
143.Va errno
144to look up the error message.
145.Pp
146The
147.Fn errx
148and
149.Fn warnx
150functions do not append an error message.
151.Pp
152The
153.Fn err ,
154.Fn verr ,
155.Fn errc ,
156.Fn verrc ,
157.Fn errx ,
158and
159.Fn verrx
160functions do not return, but exit with the value of the argument
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 errno information string and exit:
180.Bd -literal -offset indent
181if ((p = malloc(size)) == NULL)
182	err(1, NULL);
183if ((fd = open(file_name, O_RDONLY, 0)) == -1)
184	err(1, "%s", file_name);
185.Ed
186.Pp
187Display an error message and exit:
188.Bd -literal -offset indent
189if (tm.tm_hour < START_TIME)
190	errx(1, "too early, wait until %s", 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(1, "%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 printf 3 ,
212.Xr strerror 3
213.Sh HISTORY
214The
215.Fn err
216and
217.Fn warn
218functions first appeared in
219.Bx 4.4 .
220The
221.Fn err_set_exit
222and
223.Fn err_set_file
224functions first appeared in
225.Fx 2.1 .
226The
227.Fn errc
228and
229.Fn warnc
230functions first appeared in
231.Fx 3.0 .
232