xref: /dragonfly/lib/libc/string/strerror.3 (revision 2038fb68) 
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32.\"     @(#)strerror.3	8.1 (Berkeley) 6/9/93
33.\" $FreeBSD: src/lib/libc/string/strerror.3,v 1.24 2007/01/09 00:28:12 imp Exp $
34.\" $DragonFly: src/lib/libc/string/strerror.3,v 1.2 2003/06/17 04:26:46 dillon Exp $
35.\"
36.Dd October 12, 2004
37.Dt STRERROR 3
38.Os
39.Sh NAME
40.Nm perror ,
41.Nm strerror ,
42.Nm strerror_r ,
43.Nm sys_errlist ,
44.Nm sys_nerr
45.Nd system error messages
46.Sh LIBRARY
47.Lb libc
48.Sh SYNOPSIS
49.In stdio.h
50.Ft void
51.Fn perror "const char *string"
52.Vt extern const char * const sys_errlist[] ;
53.Vt extern const int sys_nerr ;
54.In string.h
55.Ft "char *"
56.Fn strerror "int errnum"
57.Ft int
58.Fn strerror_r "int errnum" "char *strerrbuf" "size_t buflen"
59.Sh DESCRIPTION
60The
61.Fn strerror ,
62.Fn strerror_r
63and
64.Fn perror
65functions look up the error message string corresponding to an
66error number.
67.Pp
68The
69.Fn strerror
70function accepts an error number argument
71.Fa errnum
72and returns a pointer to the corresponding
73message string.
74.Pp
75The
76.Fn strerror_r
77function renders the same result into
78.Fa strerrbuf
79for a maximum of
80.Fa buflen
81characters and returns 0 upon success.
82.Pp
83The
84.Fn perror
85function finds the error message corresponding to the current
86value of the global variable
87.Va errno
88.Pq Xr intro 2
89and writes it, followed by a newline, to the
90standard error file descriptor.
91If the argument
92.Fa string
93is
94.Pf non- Dv NULL
95and does not point to the null character,
96this string is prepended to the message
97string and separated from it by
98a colon and space
99.Pq Dq Li ":\ " ;
100otherwise, only the error message string is printed.
101.Pp
102If the error number is not recognized, these functions return an error message
103string containing
104.Dq Li "Unknown error:\ "
105followed by the error number in decimal.
106The
107.Fn strerror
108and
109.Fn strerror_r
110functions return
111.Er EINVAL
112as a warning.
113Error numbers recognized by this implementation fall in
114the range 0 <
115.Fa errnum
116<
117.Fa sys_nerr .
118.Pp
119If insufficient storage is provided in
120.Fa strerrbuf
121(as specified in
122.Fa buflen )
123to contain the error string,
124.Fn strerror_r
125returns
126.Er ERANGE
127and
128.Fa strerrbuf
129will contain an error message that has been truncated and
130.Dv NUL
131terminated to fit the length specified by
132.Fa buflen .
133.Pp
134The message strings can be accessed directly using the external
135array
136.Va sys_errlist .
137The external value
138.Va sys_nerr
139contains a count of the messages in
140.Va sys_errlist .
141The use of these variables is deprecated;
142.Fn strerror
143or
144.Fn strerror_r
145should be used instead.
146.Sh SEE ALSO
147.Xr intro 2 ,
148.Xr psignal 3
149.Sh STANDARDS
150The
151.Fn perror
152and
153.Fn strerror
154functions conform to
155.St -isoC-99 .
156The
157.Fn strerror_r
158function conforms to
159.St -p1003.1-2001 .
160.Sh HISTORY
161The
162.Fn strerror
163and
164.Fn perror
165functions first appeared in
166.Bx 4.4 .
167The
168.Fn strerror_r
169function was implemented in
170.Fx 4.4
171by
172.An Wes Peters Aq wes@FreeBSD.org .
173.Sh BUGS
174For unknown error numbers, the
175.Fn strerror
176function will return its result in a static buffer which
177may be overwritten by subsequent calls.
178.Pp
179The return type for
180.Fn strerror
181is missing a type-qualifier; it should actually be
182.Vt const char * .
183.Pp
184Programs that use the deprecated
185.Va sys_errlist
186variable often fail to compile because they declare it
187inconsistently.
188