xref: /minix3/lib/libc/string/strerror.3 (revision 0a6a1f1d05b60e214de2f05a7310ddd1f0e590e7)

.\" $NetBSD: strerror.3,v 1.18 2015/05/09 19:01:53 dholland Exp $
.\"
.\" Copyright (c) 1980, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" the American National Standards Committee X3, on Information
.\" Processing Systems.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"     @(#)strerror.3	8.1 (Berkeley) 6/9/93
.Dd May 9, 2015
.Dt STRERROR 3
.Os
.Sh NAME
.Nm perror ,
.Nm strerror ,
.Nm strerror_r ,
.Nm sys_errlist ,
.Nm sys_nerr
.Nd system error messages
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdio.h
.Ft void
.Fn perror "const char *string"
.In errno.h
.Vt extern const char * const sys_errlist[] ;
.Vt extern const int sys_nerr ;
.In string.h
.Ft "char *"
.Fn strerror "int errnum"
.Ft int
.Fn strerror_r "int errnum" "char *strerrbuf" "size_t buflen"
.Sh DESCRIPTION
The
.Fn strerror ,
.Fn strerror_r ,
and
.Fn perror
functions look up the language-dependent error message
string corresponding to an error number.
.Pp
The
.Fn strerror
function accepts an error number argument
.Fa errnum
and returns a pointer to the corresponding
message string.
.Pp
The
.Fn strerror_r
function renders the same result into
.Fa strerrbuf
for a maximum of
.Fa buflen
characters and returns 0 upon success.
.Pp
The
.Fn perror
function finds the error message corresponding to the current
value of the global variable
.Va errno
.Pq Xr intro 2
and writes it, followed by a newline, to the
standard error file descriptor.
If the argument
.Fa string
is
.Pf non- Dv NULL
and does not point to the nul character,
this string is prepended to the message
string and separated from it by
a colon and space
.Pq Dq Li ":\ " ;
otherwise, only the error message string is printed.
Note that in most cases the
.Xr err 3
and
.Xr warn 3
family of functions is preferable to
.Fn perror ;
they are more flexible and also print the program name.
.Pp
If the error number is not recognized, these functions pass an error message
string containing
.Dq Li "Unknown error:\ "
followed by the error number in decimal.
To warn about this,
.Fn strerror
sets
.Dv errno
to
.Er EINVAL ,
and
.Fn strerror_r
returns
.Er EINVAL .
Error numbers recognized by this implementation fall in
the range 0 \*[Lt]
.Fa errnum
\*[Lt]
.Fa sys_nerr .
.Pp
If insufficient storage is provided in
.Fa strerrbuf
(as specified in
.Fa buflen )
to contain the error string,
.Fn strerror_r
returns
.Er ERANGE
and
.Fa strerrbuf
will contain an error message that has been truncated and
.Dv NUL
terminated to fit the length specified by
.Fa buflen .
.Pp
The message strings can be accessed directly using the external
array
.Va sys_errlist .
The external value
.Va sys_nerr
contains a count of the messages in
.Va sys_errlist .
The use of these variables is deprecated;
.Fn strerror
or
.Fn strerror_r
should be used instead.
.Sh SEE ALSO
.Xr intro 2 ,
.Xr err 3 ,
.Xr psignal 3 ,
.Xr warn 3
.Sh STANDARDS
The
.Fn perror
and
.Fn strerror
functions conform to
.St -isoC-99 .
The
.Fn strerror_r
function conforms to
.St -p1003.1-2001 .
.Sh HISTORY
The
.Fn perror
function first appeared in
.At v4 .
The
.Fn strerror
function first appeared in
.Bx 4.3 Reno .
The
.Fn strerror_r
function first appeared in
.Nx 4.0 .
.Sh BUGS
For unknown error numbers, the
.Fn strerror
function will return its result in a static buffer which
may be overwritten by subsequent calls.
.Pp
The return type for
.Fn strerror
is missing a type-qualifier; it should actually be
.Vt const char * .
.Pp
Programs that use the deprecated
.Va sys_errlist
variable often fail to compile because they declare it
inconsistently.