xref: /freebsd/lib/libc/string/strerror.3 (revision 05c7a37afb48ddd5ee1bd921a5d46fe59cc70b15)
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36.\"     @(#)strerror.3	8.1 (Berkeley) 6/9/93
37.\"
38.Dd June 9, 1993
39.Dt STRERROR 3
40.Os BSD 4
41.Sh NAME
42.Nm perror ,
43.Nm strerror ,
44.Nm sys_errlist ,
45.Nm sys_nerr
46.Nd system error messages
47.Sh SYNOPSIS
48.Fd #include <stdio.h>
49.Ft void
50.Fn perror "const char *string"
51.Vt extern char *sys_errlist[];
52.Vt extern int sys_nerr;
53.Fd #include <string.h>
54.Ft char *
55.Fn strerror "int errnum"
56.Sh DESCRIPTION
57The
58.Fn strerror
59and
60.Fn perror
61functions look up the error message string corresponding to an
62error number.
63.Pp
64The
65.Fn strerror
66function accepts an error number argument
67.Fa errnum
68and
69returns a pointer to the corresponding
70message string.
71.Pp
72The
73.Fn perror
74function finds the error message corresponding to the current
75value of the global variable
76.Va errno
77.Pq Xr intro 2
78and writes it, followed by a newline, to the
79standard error file descriptor.
80If the argument
81.Fa string
82is
83.Pf non- Dv NULL ,
84it is prepended to the message
85string and separated from it by
86a colon and space
87.Pq Ql \&:\ \& .
88If
89.Fa string
90is
91.Dv NULL ,
92only the error message string is printed.
93.Pp
94If
95.Fa errnum
96is not a recognized error number,
97the error message string will contain
98.Dq Li "Unknown error:\0
99followed by the error number in decimal.
100.Pp
101The message strings can be accessed directly using the external
102array
103.Fa sys_errlist .
104The external value
105.Fa sys_nerr
106contains a count of the messages in
107.Fa sys_errlist .
108The use of these variables is deprecated;
109.Fn strerror
110should be used instead.
111.Sh SEE ALSO
112.Xr intro 2 ,
113.Xr psignal 3
114.Sh HISTORY
115The
116.Fn strerror
117and
118.Fn perror
119functions first appeared in 4.4BSD.
120.Sh BUGS
121For unknown error numbers, the
122.Fn strerror
123function will return its result in a static buffer which
124may be overwritten by subsequent calls.
125