248 lines
6.0 KiB
Groff
248 lines
6.0 KiB
Groff
.\" Copyright (c) 1980, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" the American National Standards Committee X3, on Information
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.\" Processing Systems.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)strerror.3 8.1 (Berkeley) 6/9/93
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.\" $FreeBSD$
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.\"
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.Dd December 17, 2020
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.Dt STRERROR 3
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.Os
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.Sh NAME
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.Nm perror ,
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.Nm strerror ,
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.Nm strerror_l ,
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.Nm strerror_r ,
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.Nm sys_errlist ,
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.Nm sys_nerr
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.Nd system error messages
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In stdio.h
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.Ft void
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.Fn perror "const char *string"
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.Vt extern const char * const sys_errlist[] ;
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.Vt extern const int sys_nerr ;
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.In string.h
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.Ft "char *"
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.Fn strerror "int errnum"
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.Ft "char *"
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.Fn strerror_l "int errnum" "locale_t"
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.Ft int
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.Fn strerror_r "int errnum" "char *strerrbuf" "size_t buflen"
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.Sh DESCRIPTION
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The
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.Fn strerror ,
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.Fn strerror_l ,
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.Fn strerror_r ,
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and
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.Fn perror
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functions look up the error message string corresponding to an
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error number.
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.Pp
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The
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.Fn strerror
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function accepts an error number argument
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.Fa errnum
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and returns a pointer to the corresponding message string
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in the current locale.
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.Fn strerror
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is not thread-safe.
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It returns a pointer to an internal static buffer that could be
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overwritten by a
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.Fn strerror
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call from another thread.
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.Pp
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The
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.Fn strerror_l
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function accepts
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.Fa errnum
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error number and
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.Fa locale
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locale handle arguments and returns a pointer to a string
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corresponding to the specified error in the given locale.
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.Fn strerror_l
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is thread-safe, its result can be only overwritten by
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another call to
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.Fn strerror_l
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from the current thread.
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.Pp
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The
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.Fn strerror_r
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function renders the same result into
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.Fa strerrbuf
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for a maximum of
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.Fa buflen
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characters and returns 0 upon success.
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.Pp
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The
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.Fn perror
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function finds the error message corresponding to the current
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value of the global variable
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.Va errno
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.Pq Xr intro 2
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and writes it, followed by a newline, to the
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standard error file descriptor.
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If the argument
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.Fa string
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is
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.Pf non- Dv NULL
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and does not point to the null character,
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this string is prepended to the message
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string and separated from it by
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a colon and space
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.Pq Dq Li ":\ " ;
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otherwise, only the error message string is printed.
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.Pp
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If the error number is not recognized, these functions return an error message
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string containing
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.Dq Li "Unknown error:\ "
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followed by the error number in decimal.
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The
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.Fn strerror
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and
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.Fn strerror_r
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functions return
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.Er EINVAL
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as a warning.
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Error numbers recognized by this implementation fall in
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the range 0 <
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.Fa errnum
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<
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.Fa sys_nerr .
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The number 0 is also recognized, although applications that take advantage of
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this are likely to use unspecified values of
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.Va errno .
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.Pp
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If insufficient storage is provided in
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.Fa strerrbuf
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(as specified in
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.Fa buflen )
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to contain the error string,
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.Fn strerror_r
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returns
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.Er ERANGE
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and
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.Fa strerrbuf
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will contain an error message that has been truncated and
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.Dv NUL
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terminated to fit the length specified by
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.Fa buflen .
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.Pp
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The message strings can be accessed directly using the external
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array
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.Va sys_errlist .
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The external value
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.Va sys_nerr
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contains a count of the messages in
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.Va sys_errlist .
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The use of these variables is deprecated;
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.Fn strerror ,
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.Fn strerror_l ,
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or
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.Fn strerror_r
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should be used instead.
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.Sh EXAMPLES
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The following example shows how to use
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.Fn perror
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to report an error.
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.Bd -literal -offset 2n
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#include <fcntl.h>
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#include <stdio.h>
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#include <stdlib.h>
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int
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main(void)
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{
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int fd;
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if ((fd = open("/nonexistent", O_RDONLY)) == -1) {
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perror("open()");
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exit(1);
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}
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printf("File descriptor: %d\en", fd);
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return (0);
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}
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.Ed
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.Pp
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When executed, the program will print an error message along the lines of
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.Ql "open(): No such file or directory" .
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.Sh SEE ALSO
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.Xr intro 2 ,
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.Xr err 3 ,
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.Xr psignal 3
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.Sh STANDARDS
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The
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.Fn perror
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and
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.Fn strerror
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functions conform to
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.St -isoC-99 .
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The
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.Fn strerror_r
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function conforms to
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.St -p1003.1-2001 .
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The
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.Fn strerror_l
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function conforms to
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.St -p1003.1-2008 .
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.Sh HISTORY
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The
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.Fn strerror
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and
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.Fn perror
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functions first appeared in
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.Bx 4.4 .
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The
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.Fn strerror_r
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function was implemented in
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.Fx 4.4
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by
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.An Wes Peters Aq Mt wes@FreeBSD.org .
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The
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.Fn strerror_l
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function was added in
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.Fx 13.0 .
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.Sh BUGS
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The
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.Fn strerror
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function returns its result in a static buffer which
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will be overwritten by subsequent calls.
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.Pp
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Programs that use the deprecated
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.Va sys_errlist
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variable often fail to compile because they declare it
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inconsistently.
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Size of the
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.Va sys_errlist
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object might increase during FreeBSD lifetime,
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breaking some ABI stability guarantees.
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